Fetal Fibronectin, Inflammatory Biomarkers, and Salivary Hormone Testing for Preterm Labor
Number: 0166
Table Of Contents
PolicyApplicable CPT / HCPCS / ICD-10 Codes
Background
References
Policy
Scope of Policy
This Clinical Policy Bulletin addresses fetal fibronectin, inflammatory biomarkers, and salivary hormone testing for preterm labor.
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Medical Necessity
Aetna considers the fetal fibronectin (fFN) immunoassay test medically necessary for evaluating symptomatic pregnant women at high-risk for preterm delivery (see background section for selection criteria). Repeat fFN immunoassay test is considered medically necessary if members remain symptomatic two or more weeks after a previous negative test.
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Experimental, Investigational, or Unproven
The following procedures are considered experimental, investigational, or unproven because the effectiveness of these approaches has not been established:
- Albumin/vitamin D-binding protein, beta-2 adrenoceptor genotyping, cervical phosphorylated insulin-like growth factor binding protein-1, as well as maternal tumor necrosis factor-α G308A polymorphism and interferon-γ A874T polymorphism for evaluating pregnant women at high-risk for preterm delivery;
- Biomarkers of intra-uterine inflammation (in amniotic fluid) including angiogenin, C-reactive protein, cytokines (e.g., interleukin-1, interleukin-6, interleukin-8), maternal matrix metalloproteinase-9, microRNA expression in the cervix, procalcitonin, and tumor necrosis factor-alpha for evaluating pregnant women at high-risk for preterm delivery;
- DNA methylation, ferritin, fructose bisphosphonate aldolase A, heat shock protein beta-1, peroxiredoxin-1, pyruvate kinase M1/M2, transferrin, uric acid and vimentin as biomarkers for preterm labor;
- Evaluation of amniotic fluid sludge (presence of free-floating hyperechogenic material within the amniotic fluid) for prediction of preterm birth;
- Evaluation of maternal systemic thiol/disulphide homeostasis for prediction of preterm birth;
- Fetal fibronectin test for routine screening of the general obstetric population and for all other indications including high-risk women who are asymptomatic for preterm labor, for identifying optimal candidates for cerclage, and following insertion of a cervical cerclage;
- Human chorionic gonadotrophin and phosphorylated insulin-like growth factor binding protein-1 (in cervico-vaginal fluid) for evaluating pregnant women at high-risk for preterm delivery.
- Lipidomic analysis (including phospholipids and sphingolipids) of cervico-vaginal fluid for prediction of preterm birth;
- Measurement of maternal serum alpha-1 antitrypsin levels for prediction of spontaneous pre-term birth;
- Measurement of plasma levels of arginines (e.g., asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and L-arginine) for prediction of spontaneous pre-term birth;
- Measurement of vaginal immune-proteome for prediction of spontaneous pre-term birth;
- Metabolomic biomarkers (e.g., ferritin, prostaglandin and vitamins) for evaluating pregnant women at high-risk for preterm delivery;
- Placental alpha-microglobulin-1 (PAMG-1; PartoSure) and phosphorylated insulin-like growth factor binding protein 1 (pIGFBP-1) for evaluating pregnant women at high-risk for preterm delivery;
- PreTRM (Sera Prognostics, Inc.) for predicting preterm birth;
- Proteomic biomarkers (e.g., 14-3-3 protein sigma, annexin A5, inter-α-trypsin inhibitor heavy chain H4, protein S100-A8, and protein S100-A12) for evaluating pregnant women at high-risk for preterm delivery;
- Salivary estriol (SalEst) test because the test results are not available rapidly enough to assist in decisions concerning the immediate care of the member;
- Salivary progesterone test for preterm birth;
- Salivary uric acid for evaluating pregnant women at high-risk for preterm delivery;
- Serum levels of angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), and the Ang-1/Ang-2 ratio levels for evaluating pregnant women at high-risk for preterm delivery;
- Testing of maternal methylenetetrahydrofolate reductase polymorphisms for prediction of preterm delivery;
- Testing of mid-trimester amniotic fluid proteins neutrophil gelatinase-associated lipocalin (NGAL) and plasminogen activator inhibitor 1 (PAI-1) for prediction of preterm delivery.
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Related Policies
Background
This policy is in accordance with the American College of Obstetricians and Gynecologists (ACOG) Committee Opinion on Fetal Fibronectin.
Fetal fibronectin (fFN) assay has recently been approved by the Food and Drug Administration (FDA) for clinical use in identifying patients at risk for preterm delivery. The fFN immunoassay is a qualitative test for the detection of fFN protein in cervico-vaginal secretions.
A number of studies have examined the value of the fFN test as a predictor of likelihood of preterm delivery in women with symptoms of preterm labor. The data indicate that a negative test has a maximal negative predictive value of approximately 96 % for not delivering within the next 2 weeks, while a positive test has a 15 to 20 % positive predictive value for preterm delivery. Despite these data, there have been no prospective interventional studies demonstrating a decrease in preterm deliveries or improved perinatal outcomes based on the knowledge of the results of this test. No study has examined the efficacy of fFN on the incidence, morbidity, and mortality of preterm delivery. However, there may be selected cases in which quickly available results may be helpful in assessing the patient's risk of preterm delivery allowing for an impact on clinical decisions.
In a Cochrane review on fFN testing for reducing the risk of preterm birth, Berghella and colleagues (2008) concluded that although fFN is commonly used in labor and delivery units to help in the management of women with symptoms of preterm labor, currently there is not sufficient evidence to recommend its use. Since this review found an association between knowledge of fFN results and a lower incidence of preterm birth before 37 weeks, further research should be encouraged.
Klebanoff and associates (2008) examined if salivary progesterone (P) or estriol (E3) concentration at 16 to 20 weeks' gestation predicts preterm birth or the response to 17alpha-hydroxyprogesterone caproate (17OHPC) and if 17OHPC treatment affected the trajectory of salivary P and E3 as pregnancy progressed. This was a secondary analysis of a clinical trial of 17OHPC to prevent preterm birth. Baseline saliva was assayed for P and E3. Weekly salivary samples were obtained from 40 women who received 17OHPC and 40 who received placebo in a multi-center randomized study of 17OHPC to prevent recurrent preterm delivery. Both low and high baseline saliva P and E3 were associated with a slightly increased risk of preterm birth. However, 17OHPC prevented preterm birth comparably, regardless of baseline salivary concentrations of P and E3. Moreover, 17OHPC did not alter the trajectory of salivary P over pregnancy, but it significantly blunted the rise in salivary E3 as well as the rise in the E3/P ratio. The authors concluded that 17OHPC flattened the trajectory of E3 in the second half of pregnancy, suggesting that the drug influences the fetoplacental unit.
Selection Criteria for Fetal Fibronectin (fFN) Immunoassay
According to the ACOG Committee on Obstetric Practice (1997), the fFN test is only appropriate for use in symptomatic pregnant women with all of the following characteristics:
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Amniotic membranes intact; and
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Cervical dilatation is minimal (less than 3 cm); and
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Sampling is performed no earlier than 24 weeks, 0 days and no later than 34 weeks, 6 days of gestation.
In addition, the fFN test is only useful if results are available quickly enough (generally considered to be under 4 hours) so that the results can assist in decisions concerning the immediate care of pregnant women.
Although a negative test appears to be useful in ruling out imminent preterm delivery (i.e., within 2 weeks), the clinical implications of a positive result have not been fully evaluated.
If the test is to be clinically useful, the results must be available from the laboratory in a timely manner (generally considered to be under 4 hours) so that the test can effect decisions concerning the immediate care of the patient. This is in accordance with the ACOG Committee Opinion, which states that “[i]f the test is to be clinically useful, the results must be available from the laboratory in a timely manner.”
ACOG does not recommend the fFN test for screening asymptomatic women to determine risk of preterm delivery. ACOG's Division of Practice Activities concluded that "this test is not recommended as a routine screening procedure for the general prenatal population". A recent clinical trial of the fFN test in 108 women at low risk of preterm delivery concluded that bi-weekly fFN determinations in asymptomatic women between 24 and 34 weeks' gestation “are of limited clinical value for the prediction of preterm birth”.
Keeler and colleagues (2009) determined the relationship between fFN testing prior to ultrasound-indicated cerclage and obstetric outcome. Singleton pregnancies between 18 and 24 weeks' gestation with an ultrasound-diagnosed short cervix (less than 25 mm) and funneling (greater than 25 %) of the chorio-amniotic membranes into the endocervical canal were analyzed. The fFN testing was performed and patients were randomized to cerclage or no-cerclage. Groups were stratified by fFN result. Cerclage patients were compared with no-cerclage patients. The primary outcome was delivery prior to 35 weeks' gestation. Spontaneous preterm birth prior to 35 weeks' gestation occurred in 15 (44.1 %) fFN-positive-cerclage patients and 16 (55.2 %) fFN-positive no-cerclage patients (p = 0.45). Similarly, it occurred in 16 (17.8 %) fFN-negative cerclage patients and 11 (17 %) fFN-no-cerclage patients (p = 0.99). The authors concluded that fFN testing did not identify optimal candidates for cerclage.
Inflammatory biomarkers are being investigated as predictors of preterm birth. Gedc and Ford (2010) stated that there is overwhelming evidence that intra-uterine infection and inflammation play an important role in the pathogenesis of spontaneous preterm labor, preterm prelabor rupture of the membranes and fetal injury resulting in long-term sequelae. Early diagnosis of subclinical infection and inflammation may therefore aid clinicians institute interventions focusing on such adverse outcomes. Biomarkers of intra-uterine inflammation (e.g., interleukin-6) although sensitive, are not specific. Thus, decision to deliver remote from term because of intra-uterine infection and/or inflammation should be based on clinical signs and/or bacterial culture or Gram stain of amniotic fluid. In patients with preterm contractions and intact membranes, the risk of delivery is 1 % within the week following a negative fFN in cervico-vaginal secretions. This aids to decide if antenatal steroids should be administered to patients presenting with preterm contractions between 24 and 34 weeks' gestation. Biomarkers in cervical secretions and amniotic fluid identify those who may benefit from cerclage when the cervix is shortened (less than 25 mm) and dilated in the second trimester. The authors concluded that so far, few interventions utilizing inflammatory biomarkers have shown clinical benefit. They noted that future efforts should focus on the quest for accurate biomarkers that can be obtained non-invasively and allow early prediction of subclinical disease to initiate appropriate risk-specific intervention.
In a case-control study nested in a large, prospective, multi-center cohort trial (n = 5,337), Kramer and colleagues (2010) examined the role of mid-trimester maternal plasma cytokines and C-reactive protein (CRP) as predictors of spontaneous preterm birth. Cohort women had an interview, examination, and venipuncture at 24 to 26 weeks. Frozen plasma samples in women with spontaneous preterm birth (n = 207) and approximately 2 term controls per case (n = 444) were analyzed using Luminex multi-analyte profiling technology. Fresh placentas were fixed, stained, and blindly assessed for histological evidence of infection/inflammation, decidual vasculopathy, and infarction, and vaginal swabs were analyzed for bacterial vaginosis and fFN concentration. High maternal matrix metalloproteinase-9 (MMP-9) concentration, but none of the other cytokines or CRP, was significantly associated with spontaneous preterm birth [adjusted odds ratio = 1.7 (1.1 to 2.4)] and showed a dose-response relation across quartiles. No association was observed, however, between maternal MMP-9 and placental infection/inflammation, bacterial vaginosis, or vaginal fFN concentration. The authors concluded that these findings require confirmation in future studies, but suggest that a systemic immune response implicating MMP-9 may have an etiologic role in spontaneous preterm birth.
Conde-Agudelo et al (2011) examined the accuracy of novel biomarkers to predict spontaneous preterm birth in women with singleton pregnancies and no symptoms of preterm labor. Electronic searches in PubMed, Embase, Cinahl, Lilacs, and Medion, references of retrieved articles, and conference proceedings were carried out. No language restrictions were applied. Observational studies that evaluated the accuracy of biomarkers proposed in the last decade to predict spontaneous preterm birth in asymptomatic women were selected. These researchers excluded studies in which biomarkers were evaluated in women with preterm labor. Two reviewers independently extracted data on study characteristics, quality, and accuracy. Data were arranged in 2 × 2 contingency tables and synthesized separately for spontaneous preterm birth before 32, 34, and 37 weeks of gestation. They used bi-variate meta-analysis to estimate pooled sensitivities and specificities, and calculated likelihood ratios (LRs). A total of 72 studies, including 89,786 women and evaluating 30 novel biomarkers, met the inclusion criteria. Only 3 biomarkers (proteome profile and prolactin in cervicovaginal fluid, and matrix metalloproteinase-8 in amniotic fluid) had positive LRs greater than 10. However, each of these biomarkers was evaluated in only 1 small study. Four biomarkers had a moderate predictive accuracy (interleukin-6 and angiogenin [a potent inducer of neovascularization], in amniotic fluid; human chorionic gonadotrophin and phosphorylated insulin-like growth factor binding protein-1, in cervico-vaginal fluid). The remaining biomarkers had low predictive accuracies. The authors concluded that none of the biomarkers evaluated in this review meet the criteria to be considered a clinically useful test to predict spontaneous preterm birth. They stated that further large, prospective cohort studies are needed to evaluate promising biomarkers such as a proteome profile in cervico-vaginal fluid.
The Royal College of Obstetricians and Gynaecologists’ clinical guideline on “Cervical cerclage” (RCOG, 2011) stated that fetal fibronectin testing following insertion of a cervical cerclage is not recommended.
- spontaneous abortion group (n = 4),
- preterm delivery group (n = 17), and
- pre-eclampsia/eclampsia group (n = 4).
There were no significant differences in IL-6, IL-8, and TNF-α between controls and study groups, regardless of the type of complication (p > 0.05). The authors concluded that mid-trimester amniotic fluid concentrations of the pro-inflammatory cytokines IL-6, IL-8, and TNF-α are not predictive of adverse pregnancy outcome in terms of spontaneous abortion, preterm delivery or pre-eclampsia/eclampsia in this study population.
Galazis and colleagues (2013) noted that preterm birth (PTB) is a major cause of neonatal mortality and morbidity. Women with polycystic ovary syndrome (PCOS) are at high-risk of PTB. There is a need for research studies to investigate the mechanisms linking PCOS and PTB, to facilitate screening, and develop novel preventative strategies. These researchers listed all the proteomic biomarkers of PTB and integrated this list with the PCOS biomarker database to identify commonly expressed biomarkers of the 2 conditions. They carried out a systematic review of PTB biomarkers and update of PCOS biomarker database. All eligible published studies on proteomic biomarkers for PTB and PCOS identified through various databases were evaluated. For the identification of the relevant studies, the following search terms were used: "proteomics", "proteomic", "preterm birth", "preterm labour", "proteomic biomarker" and "polycystic ovary syndrome". This search was restricted to humans only. A database on proteomic biomarkers for PTB was created while an already existing PCOS biomarker database was updated. The 2 databases were integrated and biomarkers that were co-expressed in both women with PCOS and PTB were identified and investigated. A panel of 6 proteomic biomarkers was similarly differentially expressed in women with PTB and women with PCOS compared to their respective controls (normal age-matched women in the case of PCOS studies and women with term pregnancy in the case of PTB studies). These biomarkers include pyruvate kinase M1/M2, vimentin, fructose bisphosphonate aldolase A, heat shock protein beta-1, peroxiredoxin-1 and transferrin. The authors concluded that these proteomic biomarkers (pyruvate kinase M1/M2, vimentin, fructose bisphosphonate aldolase A, heat shock protein beta-1, peroxiredoxin-1 and transferrin) can be potentially used to better understand the pathophysiological mechanisms linking PCOS and PTB. This would help to identify subgroups of women with PCOS at risk of PTB and hence the potential of developing preventative strategies.
Clowse et al (2013) stated that while increased disease activity is the best predictor of PTB in women with systemic lupus erythematosus (SLE), even women with low disease activity are at increased risk of this complication. Biomarkers that would identify at-risk pregnancies could allow interventions to prevent PTB. In this study, measures of SLE activity, inflammation, placental health and renal function between 20 and 28 weeks gestation (mid-gestation) were correlated to PTB and gestational age at delivery in a prospective cohort of pregnant women with SLE. Of the 40 pregnancies in 39 women, all with mild-moderate SLE disease, 9 (23.7 %) of the 38 live births were delivered preterm. Low C4 was the only marker of SLE activity associated with younger gestational age at delivery. Elevated ferritin and lower estradiol correlated with younger gestational age at delivery. Renal function remained normal during all pregnancies at mid-gestation and did not correlate with PTB. Higher serum uric acid, however, correlated with younger gestational age at delivery. The authors concluded that in women with SLE with mild-moderate disease activity, ferritin, estradiol and uric acid levels at mid-gestation may predict PTB. They stated that these markers may prove to be clinically useful in identifying pregnancies at particularly high-risk for adverse outcomes.
Bastek and Elovitz (2013) stated that biomarkers associated with spontaneous PTB and pre-eclampsia have been discovered in patients who experience these adverse obstetrical outcomes. The identification of such biomarkers holds promise in both facilitating the early identification of those patients at greatest risk and enhancing the understanding of these disease processes to determine therapeutic interventions. These investigators reviewed the existing literature to determine the utility of biomarkers in the risk stratification of spontaneous PTB and pre-eclampsia. They found that despite the promise of some biomarkers in identifying patients at increased risk for spontaneous PTB and/or pre-eclampsia, the use of biomarkers in clinical practice to predict adverse obstetrical outcome remains challenging. Although data from small discovery studies may be encouraging, progress with biomarker research remains limited by the lack of validation of these discovered biomarkers. Furthermore, owing to the heterogeneity of existing studies, generalizable conclusions are difficult to understand, meta-analyses are challenging to perform, and agreement on cut-point standardization is difficult. The authors concluded that the identification of an abnormal biomarker level does not guarantee whether or when an adverse clinical event might occur. The lack of understanding of the true etiologies of these disease processes resulting in the absence of definitive interventions to prevent spontaneous PTB and pre-eclampsia from occurring.
Schneuer et al (2014) evaluated angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), and the Ang-1/Ang-2 ratio levels in the first trimester of pregnancy, their association with adverse pregnancy outcomes, and their predictive accuracy. This cohort study measured serum Ang-1 and Ang-2 levels in 4,785 women with singleton pregnancies attending first trimester screening in New South Wales, Australia. Multi-variate logistic regression models were used to assess the association and predictive accuracy of serum biomarkers with subsequent adverse pregnancy outcomes (small for gestational age, PTB, pre-eclampsia, miscarriage greater than 10 weeks, and stillbirth). Median (interquartile range) levels for Ang-1, Ang-2, and the Ang-1/Ang-2 ratio for the total population were 19.6 ng/ml (13.6 to 26.4), 15.5 ng/ml (10.3 to 22.7), and 1.21 (0.83 to 1.73), respectively. Maternal age, weight, country of birth, and socioeconomic status significantly affected Ang-1, Ang-2, and the Ang-1/Ang-2 ratio levels. After adjusting for maternal and clinical risk factors, women with low Ang-2 levels (less than 10th percentile) and high Ang-1/Ang-2 ratio (greater than 90th percentile) had increased risk of developing most adverse pregnancy outcomes. Compared with the Ang-1/Ang-2 ratio alone, maternal and clinical risk factors had better predictive accuracy for most adverse pregnancy outcomes. The exception was miscarriage (Ang-1/Ang-2 ratio area under receiver operating characteristic curve = 0.70; maternal risk factors = 0.58). Overall, adding the Ang-1/Ang-2 ratio to maternal risk factors did not improve the ability of the models to predict adverse pregnancy outcomes. The authors concluded that these findings suggested that the Ang-1/Ang-2 ratio in first trimester is associated with most adverse pregnancy outcomes, but do not predict outcomes any better than clinical and maternal risk factor information.
Kacerovsky et al (2014) analyzed the findings of studies on proteomic biomarkers for spontaneous PTB. Three electronic databases (Medline, Embase, and Scopus) were searched for studies in any language reporting the use of proteomic biomarkers for PTB published between January 1994 and December 2012. Retrieved citations were screened, and relevant studies were selected for full-text reading, in triplicate. The search yielded 529 citations, 51 were selected for full-text reading and 8 studies were included in the review. A total of 64 dysregulated proteins were reported. Only 14-3-3 protein sigma, annexin A5, protein S100-A8, protein S100-A12, and inter-α-trypsin inhibitor heavy chain H4 were reported in more than 1 study, but results could not be combined due to heterogeneity in type of sample and analytical platform. The authors concluded that according to the existing literature, there are no specific proteomic biomarkers capable of accurately predicting PTB.
C-Reactive Protein and Procalcitonin
Dulay and colleagues (2015) stated that the arsenal of maternal and amniotic fluid (AF) immune response to local or systemic infection includes among others the acute-phase reactants IL-6, CRP and procalcitonin (PCT). If these molecules can be used as non-invasive biomarkers of intra-amniotic infection (IAI) in the subclinical phase of the disease remains incompletely known. These researchers used time-matched maternal serum, urine and AF from 100 pregnant women who had an amniocentesis to rule out IAI in the setting of preterm labor, preterm premature rupture of membranes (PPROM) or systemic inflammatory response (SIR: pyelonephritis, appendicitis, pneumonia) to infection. Cord blood was analyzed in a subgroup of cases. These investigators used sensitive immunoassays to quantify the levels of inflammatory markers in the maternal blood, urine and AF compartment. Microbiological testing and placental pathology was used to establish infection and histological chorio-amnionitis. Procalcitonin was not a useful biomarker of IAI in any of the studied compartments. Maternal blood IL-6 and CRP levels were elevated in women with subclinical IAI. Compared to clinically manifest chorio-amnionitis group, women with SIR have higher maternal blood IL-6 levels rendering some marginal diagnostic benefit for this condition. Urine was not an useful biological sample for assessment of IAI using any of these 3 inflammatory biomarkers. The authors concluded that in women with subclinical IAI, the large overlapping confidence intervals (CIs) and different cut-offs for the maternal blood levels of IL-6, CRP and PCT likely made interpretation of their absolute values difficult for clinical decision-making.
Furthermore, an UpToDate review on “Diagnosis of preterm labor and overview of preterm birth” (Lockwood, 2015) does not mention CRP and procalcitonin as diagnostic tools.
Interleukin-1
Nadeau-Vallee et al (2016) noted that PTB is a leading cause of neonatal mortality and morbidity worldwide, and represents a heavy economic and social burden. Despite its broad etiology, PTB has been firmly linked to inflammatory processes. Pro-inflammatory cytokines are produced in gestational tissues in response to stressors and can prematurely induce uterine activation, which precedes the onset of preterm labor. Of all cytokines implicated, interleukin (IL)-1 has been largely studied, revealing a central role in preterm labor. However, currently approved IL-1-targeting therapies have failed to show expected efficacy in pre-clinical studies of preterm labor. The authors summarized animal and human studies in which IL-1 or IL-1-targeting therapeutics were implicated with preterm labor; focused on novel IL-1-targeting therapies and diagnostic tests; and developed the case for commercialization and translation means to hasten their development.
Also, an UpToDate review on “Diagnosis of preterm labor and overview of preterm birth” (Lockwood, 2015) does not mention IL-1 as a diagnostic tool.
MicroRNA Expression in the Cervix
Sanders et al (2015) stated that PTB is a leading cause of infant mortality and can lead to poor life-long health and adverse neurodevelopmental outcomes. The pathophysiologic mechanisms that precede preterm labor remain elusive, and the role that epigenetic phenomena play is largely unstudied. These researchers examined the association between microRNA (miRNA) expression levels in cervical cells obtained from swabs collected during pregnancy and the length of gestation. They analyzed cervical samples obtained between 16 and 19 weeks of gestation from 53 women in a prospective cohort from Mexico City, and followed them until delivery. Cervical miRNA was extracted and expression was quantified using the NanoString nCounter Analysis System. Linear regression models were used to examine the association between miRNA expression levels and gestational age at delivery, adjusted for maternal age, education, parity, body mass index, smoke exposure, and inflammation assessed on a Papanicolaou smear. These investigators identified 6 miRNAs that were significantly associated with gestational age at the time of delivery, including miR-21, 30e, 142, 148b, 29b, and 223. Notably, per each doubling in miR-21 expression, gestations were 0.9 (95 % confidence interval [CI]: 0.2 to 1.5) days shorter on average (p = 0.009). Per each doubling in miR-30e, 142, 148b, 29b, and 223 expression, gestations were shorter by 1.0 to 1.6 days. The predicted targets of the miRNAs were enriched for molecules involved in DNA replication and inflammatory processes. The authors concluded that the levels of specific miRNAs in the human cervix during pregnancy are predictive of gestational age at delivery, and should be validated in future studies as potential biomarkers of preterm birth risk.
Elovitz et al (2015) examined if miRNA profiles in maternal blood are different in women who are destined to have a preterm, compared with a term, birth. A nested case-control study was performed with maternal serum that was collected as part of a larger prospective cohort. MiRNA expression profiles in maternal serum were compared between women who ultimately had a preterm birth (n = 40) compared with term birth (n = 40). MiRNA expression profiles were created with the use of the Affymetrix GeneChip miRNA Array. The data were analyzed with the significance of analysis of microarrays and principle components analyses. A false discovery rate of 20 % was used to determine the most differentially expressed miRNAs. Of the 5,640 miRNAs that were analyzed on the array, 4 miRNAs were significantly different between cases and control subjects; 2 of the 4 miRNAs were mature miRNAs. The fold difference in expression was less than 2 for all 4 miRNAs. The authors concluded that miRNA profiles in maternal blood were not significantly different in women who were destined to have a preterm, compared with a term, birth. They stated that miRNAs in maternal blood are unlikely to become clinically useful biomarkers for the prediction of PTB.
Also, an UpToDate review on “Diagnosis of preterm labor and overview of preterm birth” (Lockwood, 2015) did not mention miRNAs diagnostic tools.
Burris et al (2023) noted that PTB remains a major public health issue affecting 10 % of all pregnancies and increases risks of neonatal morbidity and mortality. Approximately 50 % to 60 % of PTBs are spontaneous, resulting from PPROM or PTL. The pathogenesis of sPTB is incompletely understood, and prediction of PTB remains elusive. Accurate prediction of PTB would reduce infant morbidity and mortality through targeted patient referral to hospitals equipped to care for pre-term infants. Two previous studies have analyzed cervical microRNAs in association with sPTB and the length of gestation, but the extent to which microRNAs serve as predictive biomarkers remains unknown. In a prospective, nested, case-control study, these researchers examined associations between cervical microRNA expression and sPTB, with the specific objective of identifying a subset of microRNAs that predict sPTB. This study included 25 cases with sPTB and 49 term controls. Controls were matched to cases in a 2:1 ratio on the basis of age, parity, and self-identified race. Cervical swabs were collected at a mean gestational age of 17.1 (4.8) weeks of gestation, and microRNAs were analyzed using a quantitative polymerase chain reaction (qPCR) array. Normalized microRNA expression was compared between cases and controls, and a false discovery rate of 0.2 was applied to account for multiple comparisons. Histopathologic analysis of slides of cervical swab samples was carried out to quantify leukocyte burden for adjustment in conditional regression models. These investigators examined the use of Relief-based unsupervised identification of top microRNAs and support vector machines to predict sPTB. They conducted microRNA enrichment analysis to examine potential biologic targets and pathways in which up-regulated microRNAs might be involved. Of the 754 microRNAs on the PCR array, 346 were detected in 75 % or greater of subjects' cervical swabs. Average cervical microRNA expression was significantly higher in cases of sPTB than in controls (p = 0.01). There were 95 significantly up-regulated individual microRNAs (greater than 2-fold change) in cases of subsequent sPTB compared with term controls (p < 0.05; q < 0.2). Notably, miR-143, miR-30e-3p, and miR-199b were all significantly up-regulated, which were consistent with the 1 previous study of cervical microRNA and sPTB. A Relief-based, novel variable (feature) selection machine learning approach had low-to-moderate prediction accuracy, with an area under the ROC of 0.71. Enrichment analysis revealed that identified microRNAs may modulate inflammatory cell signaling. The authors concluded that in this trial of cervical microRNA expression and sPTB, these researchers identified a global increase in microRNA expression and up-regulation of 95 distinct microRNAs in association with subsequent sPTB. Moreover, these investigators stated that larger and more diverse studies are needed to determine the ability of microRNAs to accurately predict sPTB, and mechanistic work to facilitate development of novel therapeutic interventions to prevent sPTB is needed.
Albumin / Vitamin D-Binding Protein
In a retrospective, cohort study, Liong and colleagues (2015) identified cervico-vaginal fluid (CVF) biomarkers predictive of spontaneous PTB in women with symptoms of preterm labor. Subjects were women with a singleton pregnancy admitted to the Emergency Department between 22 and 36 weeks of gestation presenting with symptoms of preterm labor. Two-dimensional electrophoresis was used to analyze the CVF proteome. Validation of putative biomarkers was performed using enzyme-linked immunosorbent assay (ELISA) in an independent cohort. Optimal concentration thresholds of putative biomarkers were determined and the predictive efficacy for PTB was compared with that of fetal fibronectin. Main outcome measure was prediction of spontaneous preterm labor within 7 days. Differentially expressed proteins were identified by proteomic analysis in women presenting with “threatened” preterm labor without cervical change who subsequently delivered preterm (n = 12 women); ELISA validation using an independent cohort (n = 129 women) found albumin and vitamin D-binding protein (VDBP) to be significantly altered between women who subsequently experienced PTB and those who delivered at term. Prediction of preterm delivery within 7 days using a dual biomarker model (albumin/VDBP) provided 66.7 % sensitivity, 100 % specificity, 100 % positive predictive value (PPV) and 96.7 % negative predictive value (NPV), compared with fetal fibronectin yielding 66.7, 87.9, 36.4 and 96.2 %, respectively (n = 64). Using the maximum number of screened samples, the predictive utility of albumin/VDBP yielded a sensitivity of 77.8 %, specificity and PPV of 100 % and NPV of 98.0 % (n = 109). The authors concluded that the dual biomarker model of albumin/VDBP is more effective than fetal fibronectin in predicting spontaneous preterm delivery in symptomatic women within 7 days. Moreover, they stated that a clinical diagnostic trial is needed to test this model on a larger population to confirm these findings and to further refine the predictive values.
Beta-2 Adrenoceptor Genotyping
In a case-control study, Miller and associates (2015) examined if beta-2 adrenoceptor (β2 AR) genotype is associated with shortening of the cervix or with PTB risk among women with a short cervix in the 2nd trimester. A total of 439 women, including 315 with short cervix and 124 with normal cervical length were included in this study. Nulliparous women with cervical length less than 30 mm upon a 16- to 22-week trans-vaginal sonogram and controls frequency-matched for race/ethnicity with cervical lengths greater than or equal to 40 mm were studied; β2 AR genotype was determined at positions encoding for amino acid residues 16 and 27. Genotype distributions were compared between case and control groups. Within the short cervix group, pregnancy outcomes were compared by genotype, with a primary outcome of PTB less than 37 weeks. Genotype data were available at position 16 for 433 women and at position 27 for 437. Using a recessive model testing for association between short cervix and genotype, and adjusted for ethnicity, there was no statistical difference between cases and controls for Arg16 homozygosity (OR 0.7, 95 % CI: 0.4 to 1.3) or Gln27 homozygosity (OR 0.9, 95 % CI: 0.3 to 2.7). Among cases, Arg16 homozygosity was not associated with protection from PTB or spontaneous PTB. Gln27 homozygosity was not associated with PTB risk, although sample size was limited. The authors concluded that β2 AR genotype did not appear to be associated with short cervical length or with PTB following the 2nd-trimester identification of a short cervix; influences on PTB associated with β2 AR genotype did not appear to involve a short cervix pathway.
Cervical Phosphorylated Insulin-Like Growth Factor Binding Protein-1
Conde-Agudelo and Romero (2016) evaluated the accuracy of the cervical phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) test to predict PTB in women with and without symptoms of preterm labor through the use of formal methods for systematic reviews and meta-analytic techniques. Data sources included PubMed, Embase, Cinahl, Lilacs, and Medion (all from inception to June 30, 2015), reference lists, conference proceedings, and Google scholar. Study eligibility criteria were cohort or cross-sectional studies that reported on the predictive accuracy of the cervical phIGFBP-1 test for PTB. Two reviewers selected studies, assessed the risk of bias, and extracted the data. Summary receiver-operating characteristic curves, pooled sensitivities and specificities, and summary likelihood ratios were generated. A total of 43 studies met the inclusion criteria, of which 15 provided data on asymptomatic women (n = 6,583) and 34 on women with an episode of preterm labor (n = 3,620). Among asymptomatic women, the predictive accuracy of the cervical phIGFBP-1 test for PTB at less than 37, less than 34, and less than 32 weeks of gestation was minimal, with pooled sensitivities and specificities and summary positive and negative likelihood ratios ranging from 14 % to 47 %, 76 % to 93 %, 1.5 to 4.4, and 0.6 to 1.0, respectively. Among women with an episode of preterm labor, the test had a low predictive performance for delivery within 7 and 14 days of testing, and PTB at less than 34 and less than 37 weeks of gestation with pooled sensitivities and specificities and summary positive and negative likelihood ratios that varied between 60 % and 68 %, 77 % and 81 %, 2.7 and 3.5, and 0.4 and 0.5, respectively. A negative test result in women with an episode of preterm labor had a low-to-moderate accuracy to identify women who are not at risk for delivering within the next 48 hours (summary negative likelihood ratio of 0.28 in all women and 0.23 in women with singleton gestations). The authors concluded that cervical phIGFBP-1 has the potential utility to identify patients with an episode of preterm labor who will not deliver within 48 hours. However, its overall predictive ability for the identification of symptomatic and asymptomatic women at risk for PTB is limited.
Maternal Tumor Necrosis Factor-α G308A Polymorphism and Interferon-γ A874T Polymorphism
Liu and colleagues (2015) examined the association between tumor necrosis factor-α (TNF-α) G308A polymorphism and interferon-γ (INF-γ) A874T polymorphism and risk of PTB by performing a meta-analysis of available studies. Articles were chosen based on PubMed, Embase, Web of science, and China Biology Medicine (CBM) databases with no language restriction from their inceptions to March 1, 2014. Specific inclusion criteria were used to evaluate articles. Meta-analysis was performed by using a random or fixed effect model with STATA 11.0 software. These researchers estimated the summary odds ratios (ORs) with its corresponding 95 % CI to assess the association. A total of 21 eligible case-control studies with 2,103 cases and 5,070 controls were finally included into this meta-analysis. Pooled analysis showed that A allele of TNF-α G308A was not associated with increased PTB risk (OR = 0.84, 95 % CI: 0.65 to 1.07, p = 0.167 for G versus A). Stratifying analysis for ethnicity and different definition of PTB also indicated that A allele was not associated with increased PTB risk. However, the meta-analysis showed that INF-γ A874T polymorphism was associated with the increased risk of PTB (OR = 1.14, 95 % CI: 1.11 to 1.73, p = 0.004 for A versus T). Stratifying analysis was not performed due to the small sample size. The authors concluded that TNF-α G308A polymorphism was not associated with an increased risk of PTB, but INF-γ A874T polymorphism may contribute to increasing susceptibility to PTB. Moreover, they stated that detection of polymorphism of INF-γ A874T might be a promising biomarker for the diagnosis and prognosis of preterm delivery.
DNA Methylation and Preterm Birth
Barcelona de Mendoza et al (2017) stated that the causes of many cases of PTB remain enigmatic. Increased understanding of how epigenetic factors are associated with health outcomes has resulted in studies examining DNA methylation (DNAm) as a contributing factor to PTB. However, few studies on PTB and DNAm have included African American women, the group with the highest rate of PTB. These researchers analyzed the existing studies on DNAm and PTB among African American women. Studies (n = 10) were limited by small sample size, cross-sectional study designs, inconsistent methodologies for epigenomic analysis, and evaluation of different tissue types across studies. African Americans comprised less than 50 % of the sample in 50 % of the studies reviewed. Despite these limitations, there was evidence for an association between DNAm patterns and PTB. The authors concluded that future research on DNAm patterns and PTB should use longitudinal study designs, repeated DNAm testing, and a clinically relevant definition of PTB and should include large samples of high-risk African American women to better understand the mechanisms for PTB in this population.
Placental Alpha-Microglobulin-1 (PAMG-1; PartoSure) and Phosphorylated Insulin-Like Growth Factor Binding Protein 1 (pIGFBP-1)
Fuchs and colleagues (2017) examined the accuracy of cervical phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) test alone or in combination with cervical length (CL), to predict PTB in symptomatic women. These researchers performed a prospective cohort study from 2012 to 2015 including singleton pregnancies with symptoms of preterm labor, intact membranes and CL of less than 25 mm at 24 to 34 weeks of gestation. Studied outcome were spontaneous delivery within 7 and 14 days of testing and spontaneous PTB at less than 34 and less than 37 weeks of gestation. Among 180 women, 21 (11.7 %) had a positive phIGFBP-1 test. Spontaneous PTB occurred within 7 days, 14 days of testing and before 34 weeks and 37 weeks in 7.8 %, 10.6 %, 12.9 % and 28.8 %, respectively. The phIGFBP-1 test had a low predictive performance for all studied outcomes varying for positive likelihood ratios (2.8 to 3.4) and negative likelihood ratios (0.8). Combining phIGFBP-1 and CL did not increase its predictive ability. After adjustment, positive phIGFBP-1 test was no more independently associated with a delivery within 7 days (p = 0.55), unlike CL of less than 15 mm (p = 0.04). The authors concluded that phIGFBP-1 test alone or in combination with CL had a low predictive accuracy to predict PTB in symptomatic women.
An UpToDate review on “Diagnosis of preterm labor” (Lockwood, 2017) states that “Like fFN, placental α-microglobulin-1 (PAMG-1) or phosphorylated insulin-like growth factor binding protein 1 (pIGFBP-1) in vaginal or cervical secretions suggests disruption of the fetal membranes (ROM or labor) and are potential markers of an increased risk of preterm birth. However, the utility of these tests has not been validated in either large or randomized clinical trials. In the largest study, which included 796 women with signs and symptoms of preterm labor, the sensitivities of PAMG-1 and fFN for spontaneous preterm birth within 7 days were 50 % (3/6) and 67 %(4/6), respectively, and specificities were 98.4 % (619/629) and 85.7 %539/629), respectively”.
In a systematic review and meta-analysis, Melchor and colleagues (2018) evaluated the accuracy of PAMG-1, fFN and phIGFBP-1 tests in predicting spontaneous PTB (sPTB) within 7 days of testing in women with symptoms of preterm labor. The test performance of each biomarker was also assessed according to pre-test probability of sPTB less than or equal to 7 days. The Cochrane, Medline, PubMed and ResearchGate bibliographic databases were searched from inception until October 2017. Cohort studies that reported on the predictive accuracy of PAMG-1, fFN and phIGFBP-1 for the prediction of sPTB within 7 days of testing in women with symptoms of preterm labor were included. Summary receiver-operating characteristics (ROC) curves and sensitivity, specificity, PPV, NPV and LR+ and LR- were generated using indirect methods for the calculation of pooled effect sizes with a bi-variate linear mixed model for the logit of sensitivity and specificity, with each diagnostic test as a co-variate, as described by the Cochrane Handbook for Systematic Reviews of Diagnostic Test Accuracy. Bi-variate mixed model pooled sensitivity of PAMG-1, fFN and phIGFBP-1 for the prediction of sPTB less than or equal to 7 days was 76 % (95 % CI: 57 to 89 %), 58 % (95 % CI: 47 to 68 %) and 93 % (95 % CI: 88 to 96 %), respectively; pooled specificity was 97 % (95 % CI: 95 to 98 %), 84 % (95 % CI: 81 to 87 %) and 76 % (95 % CI: 70 to 80 %) respectively; pooled PPV was 76.3 % (95 % CI: 69 to 84 %) (p < 0.05), 34.1 % (95 % CI: 29 to 39 %) and 35.2 % (95 % CI: 31 to 40 %), respectively; pooled NPV was 96.6 % (95 % CI: 94 to 99 %), 93.3 % (95 % CI: 92 to 95 %) and 98.7 % (95 % CI: 98 to 99 %), respectively; pooled LR+ was 22.51 (95 % CI: 15.09 to 33.60) (p < 0.05), 3.63 (95 % CI: 2.93 to 4.50) and 3.80 (95 % CI: 3.11 to 4.66), respectively; and pooled LR- was 0.24 (95 % CI: 0.12 to 0.48) (p < 0.05), 0.50 (95 % CI: 0.39 to 0.64) and 0.09 (95 % CI: 0.05 to 0.16), respectively. The areas under the ROC curves for PAMG-1, fFN and phIGFBP-1 for sPTB less than or equal to 7 days were 0.961, 0.874 and 0.801, respectively. The authors concluded that in the prediction of sPTB within 7 days of testing in women with signs and symptoms of preterm labor, the PPV of PAMG-1 was significantly higher than that of phIGFBP-1 or fFN. Other diagnostic accuracy measures did not differ between the 3 biomarker tests. As prevalence affects the predictive performance of a diagnostic test, use of a highly specific assay for a lower-prevalence syndrome such as sPTB may optimize management.
The authors stated that this study had several drawbacks. First, it may be under-powered, as these researchers were unable to attain convergence in the low‐risk and intermediate‐risk groups. Thus, the model had to be simplified to include random study effects only, without random effects for sensitivity and specificity by study. Additionally, the 3 risk groups showed variation in sensitivity and specificity. These metrics should not be dependent on the prevalence of the disease, as compared to predictive values. This heterogeneity could be due to within‐study error and/or other population characteristics. The reason for variation across populations should be further investigated. Second, the 3 biomarkers were not studied in the same number of subjects. Furthermore, only 45 % of studies were considered to have a low risk of bias. Studies that did not specify the definition of PTB as spontaneous were ranked as having higher risk of bias as they may have included medically indicated deliveries. This effect was expected to be minimal, given that few studies fell into this group, and more than 2/3 of PTBs were spontaneous. Given the complexity and heterogeneity of available studies, the performance end-points were limited to sPTB less than or equal to 7 days of testing, as not all studies included information for other end-points, such as sPTB within 48 hours or 14 days of testing. Alternative analysis methods may produce different pooled estimates from those found in the present study. A simple pooled estimate may be obtained directly by summing numerators and denominators from the raw data across studies, but had severe limitations as it assumed lack of heterogeneity across the studies. Therefore, random‐effects models are needed to describe variability in test accuracy across studies, which in addition assumes independence of sensitivity and specificity. The bi-variate mixed‐effects model of Reitsma et al (2005) is a widely accepted method for meta‐analysis of diagnostic tests, as it overcomes the limitations of simple pooling by jointly modeling sensitivity and specificity. Apart from accounting for between‐study variability due to both random error and inherent differences between the studies owing to different design, population or study procedures, the bi-variate mixed‐effects model method also allowed for inclusion of co-variates. Finally, this review did not examine the impact of test performance on patient management and resource economics. This is an area for future research. Additionally, the heterogeneity of each test's performance using individual‐patient data and meta‐regression techniques looking at co-variates such as gestational age, contraction frequency and CL at presentation should also be examined in future studies.
Furthermore, an UpToDate review on “Preterm labor: Clinical findings, diagnostic evaluation, and initial treatment” (Lockwood, 2018) states that “Like fFN, placental α-microglobulin-1 (PAMG-1) or phosphorylated insulin-like growth factor binding protein 1 (pIGFBP-1) in vaginal or cervical secretions suggests disruption of the fetal membranes (ROM or labor) and are potential markers of an increased risk of preterm birth. However, the utility of these tests has not been validated in either large or randomized clinical trials. In the largest study, which included 796 women with signs and symptoms of preterm labor, the sensitivities of PAMG-1 and fFN for spontaneous preterm birth within 7 days were 50 %(3/6) and 67 % (4/6), respectively, and specificities were 98.4 % (619/629) and 85.7 % (539/629), respectively”.
In a systematic review, Gates and co-workers (2019) examined the evidence on the effectiveness and accuracy of predictive tests for preterm delivery among symptomatic women. This study included English-language systematic reviews (SRs) on any predictive test for preterm delivery among symptomatic women and primary studies for PAMG-1. PubMed, Wiley Cochrane Library, the Centre for Reviews and Dissemination Database, the National Guidelines Clearinghouse, and the TRIP database were searched for SRs; PubMed and PubMed Central via the Wiley Cochrane Library were searched for primary studies. One reviewer performed study selection, with input from a second reviewer when needed. One reviewer appraised study quality and extracted: study characteristics (i.e., country, funding source, study design [primary studies] or synthesis method [SRs], study appraisal method [SRs]), population characteristics, index test(s) and cut-off points used, comparator(s) or reference standard(s), and outcomes. A 2nd reviewer assessed a random 10 % sample. The authors synthesized the findings narratively. Of 451 unique records, the review included 22 (17 SRs, 5 primary studies). For effectiveness, there was evidence for use of transvaginal ultrasound (TVUS) cervical length assessment (15 to 25 mm cut-off point) in reducing incidence of preterm delivery at less than 37 weeks (relative risk [RR] 0.64; 95% CI: 0.44 to 0.94, 1 SR of 3 trials; n = 287) but lack of support for cervicovaginal fFN. In terms of accuracy, 1 high-quality study within a best-evidence SR showed that cervical length measurement was useful to predict delivery within 48 hours (LR+ 6.43, 95% CI: 5.17 to 8.00; LR- 0.03, 95% CI: 0.00 to 0.42; n = 510) and 7 days (LR+ 8.61, 95% CI: 6.65 to 11.14; LR- 0.03, 95% CI: 0.00 to 0.18; n = 510). Accuracy of PAMG-1 testing was not supported for most end-points. The authors concluded that some evidence supports the effectiveness of cervical length as a predictor of preterm delivery in symptomatic women; and evidence for most tests is limited in quality and quantity.
In a systematic review and economic evaluation, Varley-Campbell and associates (2019) examined the test accuracy, clinical effectiveness and cost-effectiveness of the diagnostic tests PartoSure (Parsagen Diagnostics Inc., Boston, MA), Actim Partus (Medix Biochemica, Espoo, Finland) and the Rapid Fetal Fibronectin (fFN) 10Q Cassette Kit (Hologic, Inc., Marlborough, MA) at thresholds ≠50 ng/ml [quantitative fFN (qfFN)] for women presenting with signs and symptoms of PTL relative to fFN at 50 ng/ml. These researchers carried out systematic reviews of the published literature for diagnostic test accuracy (DTA) studies of PartoSure, Actim Partus and qfFN for predicting PTB, the clinical effectiveness following treatment decisions informed by test results and economic evaluations of the tests. A model-based economic evaluation was also performed to extrapolate long-term outcomes from the results of the diagnostic tests. The model followed the structure of the model that informed the 2015 National Institute for Health and Care Excellence guidelines on PTL diagnosis and treatment, but with antenatal steroids use, as opposed to tocolysis, driving health outcomes. A total of 20 studies were identified evaluating DTA against the reference standard of delivery within 7 days and 7 studies were identified evaluating DTA against the reference standard of delivery within 48 hours; 2 studies assessed 2 of the index tests within the same population; 1 study demonstrated that depending on the threshold used, qfFN was more or less accurate than Actim Partus, whereas the other indicated little difference between PartoSure and Actim Partus. No study assessing qfFN and PartoSure in the same population was identified. The test accuracy results from the other included studies revealed a high level of uncertainty, primarily attributable to substantial methodological, clinical and statistical heterogeneity between studies. No study compared all 3 tests simultaneously. No clinical effectiveness studies evaluating any of the 3 biomarker tests were identified. One partial economic evaluation was identified for predicting PTB. It examined the number needed to treat to prevent a respiratory distress syndrome case with a “treat-all” strategy, relative to testing with qualitative fFN. Because of the lack of data, the de-novo model involved the assumption that management of pregnant women fully adhered to the results of the tests. In the base-case analysis for a woman at 30 weeks' gestation, Actim Partus had lower health-care costs and fewer quality-adjusted life-years (QALYs) than qfFN at 50 ng/ml, reducing costs at a rate of £56,030 per QALY lost compared with qfFN at 50 ng/ml. PartoSure was less costly than Actim Partus while being equally effective, but this was based on diagnostic accuracy data from a small study. Treatment with qfFN at 200 ng/ml and 500 ng/ml resulted in lower cost savings per QALY lost relative to fFN at 50 ng/ml than treatment with Actim Partus. In contrast, qfFN at 10 ng/ml increased QALYs, by 0.002, and had a cost per QALY gained of £140,267 relative to fFN at 50 ng/ml. Similar qualitative results were obtained for women presenting at different gestational ages. The authors concluded that there is a high degree of uncertainty surrounding the test accuracy and cost-effectiveness results. They were aware of 4 ongoing United Kingdom trials, 2 of which plan to enroll more than 1,000 subjects. The findings of these trials may significantly alter the findings presented here.
Rouholamin and co-workers (2020) noted that PTB is common, occurring in over 10 % of all live-births globally, and is increasing worldwide. The limitations of traditional biomarkers of PTB, such as fFN and phosphorylated insulin-like growth factor-binding protein-1 (phIGFBP-1) have been well demonstrated in the literature; thus, augmenting clinical assessment with newer biomarkers, such as PAMG-1 (PartoSure) has the potential to improve disease monitoring and the best interventions. The present expert opinion evaluated the utility and limitations of PAMG-1 (PartoSure) as a biomarker for PTB in light of the current literature. These investigators stated that although fFN, phIGFBP-1 and PAMG-1 test (PartoSure) had similar NPV and LR-, the PAMG-1 test (PartoSure) had the highest specificity, PPV, and LR+ across all at-risk pregnant women. The authors concluded that although the findings of this review may be encouraging, the PAMG-1 test (PartoSure) should not be interpreted as absolute evidence for prediction of PTB. The PAMG-1 test (PartoSure) result should always be used in conjunction with information available from the clinical evaluation of the pregnant woman and other diagnostic procedures such as cervical examination, assessment of uterine activity, and evaluation of other risk factors.
Marie and colleagues (2020) noted that threatened preterm delivery (TPD) is the leading cause of inpatient admissions during pregnancy; therefore, the ability to predict the risk of imminent preterm delivery is a major priority in obstetrics. The aim of this trial is to examine the diagnostic performance of the test to detect PAMG-1 for the prediction of delivery within 7 days in women with TPD. This is a prospective, multi-center diagnostic study. Inclusion criteria are singleton pregnancy, gestational age between 24 + 0 and 33 + 6 weeks inclusive, cervical measurement 25 mm or less assessed by TVUS (with or without uterine contractions), clinically intact membranes and cervical dilatation of less than 3 cm assessed by digital examination. According to the current protocol, when a women presents with TPD and the diagnosis is confirmed by TVUS, a vaginal sample to test for genital infection is carried out. At the same time, the midwife will perform the PartoSure test. To perform this analysis, a sample of cervicovaginal secretions is taken with the vaginal swab furnished in the test kit. The primary outcome is the specificity of the PartoSure test of women who give birth more than 7 days after their hospitalization for TPD. The secondary outcomes are the sensitivity, PPV, and NPV of the PartoSure test and the factors associated with false positives (with a univariate logistic regression model). Starting with the hypothesis of an anticipated specificity of 89 %, if these researchers want to estimate this specificity with a confidence interval of ± 5 %, they will need 151 women who do not give birth within 7 days. These investigators therefore decide to include 400 women over a period of 2 years to have a larger number of events (deliveries within 7 days). The authors stated that different tests already used such as fFN and phIGFBP-1, are not sufficiently relevant to recommend their use in daily practice. The different studies of PAMG-1 described above thus provide support for the use of this substance, tested by PartoSure. Nonetheless, other larger studies are needed to validate its use in daily practice and the MAPOSURE Study could answer this question. These researchers stated that there is no data monitoring committee because it is a prospective, multi-center, non-interventional diagnostic study; it will be conducted in compliance with the current approved version of the protocol.
In a systematic review and meta-analysis, Pirjani and colleagues (2021) examined the accuracy of the PAMG-1 to predict PTB in women with symptoms of PTB. These investigators carried out a comprehensive search of medical bibliographic data-bases to identify observational studies that reported on the predictive accuracy of PAMG-1 for PB; 2 researchers independently evaluated studies, assessed quality of studies, and extracted data. Summary receiver operating characteristic (SROC) curves, pooled sensitivities, specificities, likelihood ratios (LR), and diagnostic odds ratio (DOR) were generated. A total of 17 studies involving 2,590 women met the inclusion criteria. Meta-analysis of 15 studies (including 1,906 women) revealed a pooled sensitivity of 66.2 % (95 % CI: 59.1 to 72.7) and specificity of 96.1 % (95 % CI: 95.1 to 97.0) with the SROC equal to 0.97 (95 % CI: 0.95 to 0.98) for prediction of delivery within 7 days of testing. The summary estimates were 15.26 (95 % CI: 11.80 to 19.75) for LR + and 0.31 (95 % CI: 0.17 to 0.55) for LR - for prediction of delivery within 7 days of testing. Pooled estimate of DOR for predicting delivery within 7 days of testing was 55.13 (95 % CI: 35.32 to 86.06). The sensitivity, specificity and the SROC of PAMG-1 pooled from 10 studies (including 1,508 women) for prediction of delivery within 14 days of testing were 64.4 % (95 % CI: 56.8 to 71.5), 96.9 % (95 % CI: 95.8 to 97.7) and 0.97 (95 % CI: 0.95 to 0.98). The overall pooled LR + and LR - of PAMG-1 for predicting delivery within 14 days of testing among the included studies were 16.72 (95 % CI: 12.03 to 23.23) and 0.42.1 (95 % CI: 0.31 to 0.56), respectively. The pooled DOR of the PAMG-1 for prediction delivery within 14 days of testing was equal to 44.65 (95 % CI: 26.30 to 75.78). The authors concluded that cervical PAMG-1 had a high accuracy to predict PB within 7 and 14 days of testing in symptomatic pregnant women.
Stubert and colleagues (2021) noted that thrombospondin 1, desmoplakin and stratifin are putative biomarkers for the prediction of PTB. In a prospective, observational, exploratory study, these researchers attempted to validate the predictive capability of these biomarkers in patients at risk of PTB. They included 109 women with symptoms of threatened spontaneous PTB between weeks 20 0/7 and 31 6/7 of gestation. Inclusion criteria were uterine contractions, CL of less than 25 mm, or a personal history of spontaneous PTB. Multiple gestations were also included. Samples of CVF were taken before performing a digital examination and transvaginal US. Levels of cervico-vaginal thrombospondin 1, desmoplakin and stratifin were quantified by ELISA. The primary endpoint was spontaneous PTB before 34 + 0 weeks of gestation. A total of 16 women (14.7 %) delivered before 34 + 0 weeks. Median levels of thrombospondin 1 were higher in samples where birth occurred before 34 weeks versus greater than or equal to 34 weeks of gestation (4,904 versus 469 pg/ml, p < 0.001). ROC analysis resulted in an area under the curve (AUC) of 0.86 (p < 0.0001). A t an optimal cut-off value of 2,163 pg/ml, sensitivity, specificity, PPV and NPV were 0.94, 0.77, 0.42 and 0.99, respectively, with an adjusted OR of 32.9 (95 % CI: 3.1 to 345, p = 0.004). Multiple gestation, CL, and preterm labor had no impact on the results. Survival analysis revealed a predictive period of more than 8 weeks. Levels of desmoplakin and stratifin did not differ between groups. The authors concluded that they were able to validate the predictive capability of thrombospondin 1 levels in CVF to estimate the risk of PTB; these findings were encouraging, and confirmation in a large multi-center study will be useful.
Maternal Methylenetetrahydrofolate Reductase Polymorphisms and Preterm Delivery
Wu and associates (2017) examined the association of maternal and neonatal methylenetetrahydrofolate reductase (MTHFR) C677T polymorphisms with PTB and low birth weight (LBW) susceptibility, respectively. These investigators carried out a systematic search of Embase, Medline, China Biological Medicine (CBN) Database, Chinese National Knowledge Infrastructure (CNKI), and Wanfang Database before June, 2016. The frequencies of maternal and neonatal MTHFR C677T genotypes in the cases and controls and other information were extracted by 2 independent investigators; ORs with 95 % CIs were adopted to estimate the relationships between MTHFR C677T polymorphisms and PTB as well as LBW by random or fixed effect models. A total of 25 studies from 20 articles concerning maternal and neonatal MTHFR C677T gene polymorphism with PTB and LBW were included in this study. Maternal MTHFR C677T polymorphism was associated with PTB risk under allele contrast (T versus C, OR = 1.36, 95 % CI: 1.02 to 1.81), homozygote (TT versus CC, OR = 1.70, 95 % CI: 1.07 to 2.68), and recessive (TT versus CT + CC, OR = 1.49, 95 % CI: 1.00 to 2.22) model, but not dominant or heterozygote model. Maternal MTHFR C677T polymorphism was also associated with LBW risk under allele contrast (OR = 1.69, 95 % CI: 1.25 to 2.28), homozygote (OR = 2.26, 95 % CI: 1.44 to 3.54), dominant (OR = 1.71, 95 % CI: 1.19 to 2.47), recessive (OR = 1.79, 95 % CI: 1.42 to 2.26) model, but not heterozygote model. No associations between neonatal MTHFR C677T polymorphism and PTB or LBW were found under all genetic models. The authors concluded that identification of maternal MTHFR C677T mutation may play a key role for primary prevention of PTB as well as LBW and screening pregnant women of high risk in developing countries.
Fang and colleagues (2018) noted that reported associations between MTHFR gene polymorphisms and preterm delivery are conflicting. In a meta-analysis, these investigators summarized the existing evidence and evaluated these associations. Eligible studies were retrieved from Medline, Embase, the CBM Database and the Cochrane Library. They calculated pooled ORs and 95 % CIs within 5 genetic models using either random-effects or fixed-effects models dependent on study heterogeneity. Potential publication bias was assessed using a Begg's test; sensitivity analysis was performed to evaluate the stability of the results. A total of 13 studies involving 4,816 mothers who experienced preterm delivery and 34,506 normal controls were included. Significant associations between MTHFR C677T polymorphism and the risk of preterm delivery were detected overall (ORT/C = 1.34, 95 % CI: 1.12 to 1.61; ORTT/CC = 1.60, 95 % CI: 1.21 to 2.11; ORCT/CC = 1.33, 95 % CI: 1.07 to 1.65; ORTT/(CC + CT) = 1.41, 95% CI 1.11-1.78; OR(TT + CT)/CC = 1.36, 95% CI 1.11-1.66) and in an Asian population (ORT/C = 1.80, 95% CI 1.24-2.62; ORTT/CC = 2.13, 95% CI 1.27-3.57; ORCT/CC = 1.93, 95% CI 1.37-2.71; OR(TT + CT)/CC = 2.03, 95 % CI: 1.49 to 2.77). Negative associations of the A1298C polymorphism were only observed among Asian pregnant women (ORC/A = 0.66, 95 % CI: 0.50 to 0.88; ORCC/AA = 0.10, 95 % CI: 0.02 to 0.53; ORCC/(AA + AC) = 0.11, 95 % CI: 0.02 to 0.57; OR(CC + AC)/AA = 0.68, 95 % CI: 0.49 to 0.94). The authors concluded that MTHFR 677 T may play a significant role in regard to the risk of preterm delivery, especially in the Asian population.
Furthermore, an UpToDate review on “Preterm labor: Clinical findings, diagnostic evaluation, and initial treatment” (Lockwood, 2018) does not mention MTHFR gene polymorphisms.
Cervical Assessment by Ultrasound for the Prevention of Preterm Birth
Berghella and Saccone (2019) noted that measurement of cervical length by ultrasound (US) is predictive of PTB. There are 3 methods of US cervical assessment: trans-vaginal (TVU), trans-abdominal (TAU), and trans-perineal (TPU, also called trans-labial). Cervical length measured by TVU is a relatively new screening test, and has been associated with better prediction of PTB than previously available tests. It is unclear if cervical length measured by US is effective for preventing PTB. This is an update of a Cochrane review last published in 2013. These researchers examined the effectiveness of antenatal management based on TVU, TAU, and TPU screening of cervical length for preventing preterm birth. For this update, they searched the Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials.gov, and the WHO International Clinical Trials Registry Platform (ICTRP) to August 30, 2018; reviewed the reference lists of all articles, and contacted experts in the field for additional and ongoing trials. These investigators included published and unpublished randomized controlled trials (RCTs) including pregnant women between the gestational ages (GA) of 14 to 32 weeks, for whom the cervical length was screened for risk of PTB with TVU, TAU, or TPU. This review focused on studies based on knowledge versus no knowledge of cervical length results, or US versus no US for cervical length. These researchers excluded studies based on interventions (e.g., progesterone, cerclage) for short cervical length. They included 7 RCTs (n = 923): 1 examined asymptomatic women with twin pregnancies; 4 included women with singleton pregnancies and symptoms of preterm labor (PTL); 1 included women with singleton pregnancies and symptoms of PPROM; and 1 included asymptomatic singletons. All trials used TVU for screening. These investigators assessed the risk of bias of the included studies as mixed, and the quality of the evidence for primary outcomes as very low for all populations. For asymptomatic women with twin pregnancies, it is uncertain whether knowledge of TVU-measured cervical length compared to no knowledge reduced PTB at less than 34 weeks (risk ratio (RR) 0.62, 95 % CI: 0.30 to 1.25; 1 study, 125 participants) because the quality of the evidence was very low. The results were also inconclusive for PTB at 36, 32, or 30 weeks; GA at birth, and other maternal and perinatal outcomes; 4 trials examined knowledge of TVU-measured cervical length of singletons with symptoms of PTL versus no knowledge. The authors were uncertain of the effects because of inconclusive results and very low-quality evidence for: PTB at less than 37 weeks (average RR 0.59, 95 % CI: 0.26 to 1.32; 2 studies, 242 participants; I² = 66 %; Tau² = 0.23). Birth occurred about 4 days later in the knowledge groups (mean difference (MD) 0.64 weeks, 95 % CI: 0.03 to 1.25; 3 trials, 290 women). The results were inconclusive for the other outcomes for which there were available data: PTB at less than 34 or 28 weeks; birth-weight less than 2,500 g; perinatal death; maternal hospitalization; tocolysis; and steroids for fetal lung maturity. The trial of singletons with PPROM (n = 92) evaluated safety of using TVU to measure cervical length in this population as its primary outcome, not its effect on management. The results were inconclusive for incidence of maternal and neonatal infections between the TVU and no US groups. In the trial of asymptomatic singletons (n = 296), in which women either received TVU or not, the results were inconclusive for PTB at less than 37 weeks (RR 1.27, 95 % CI: 0.61 to 2.61; I² = 0%), GA at birth, and other perinatal and maternal outcomes. These researchers down-graded evidence for limitations in study design, inconsistency between the trials, and imprecision, due to small sample size and wide CIs crossing the line of no effect. No trial compared the effect of knowledge of the CL with no knowledge of CL in other populations, such as asymptomatic women with singleton pregnancies, or symptomatic women with twin pregnancies. The authors concluded that there were limited data on the effects of knowing the cervical length, measured by US, for preventing PTB, which precluded them from drawing any conclusions for women with asymptomatic twin or singleton pregnancies, singleton pregnancies with PPROM, or other populations and clinical scenarios. Limited evidence suggested that knowledge of TVU-measured cervical length, used to inform the management of women with singleton pregnancies and symptoms of PTL, appeared to prolong pregnancy by about 4 days over women in the no knowledge groups. These researchers stated that future studies could look at specific populations separately (e.g., singleton versus twins; symptoms versus no symptoms of PTL), report on all pertinent maternal and perinatal outcomes, and include cost-effectiveness analyses. Most importantly, future studies should include a clear protocol for management of women based on TVU-measured cervical length.
Cervico-Vaginal Placental α-Macroglobulin-1 Combined with Cervical Length Assessment for the Prediction of Preterm Birth
Radan and colleagues (2020) stated that PTB is a major cause of neonatal morbidity and mortality. There is an urgent need to accurately predict imminent delivery to enable necessary interventions such as tocolytic, glucocorticoid, and magnesium sulfate administration. In a prospective, observational study, these researchers examined placental α-macroglobulin-1 as a new diagnostic marker in the prediction of PTB. This trial was carried out in women with intact membranes between 24+0 and 36+6 weeks of gestation. These investigators included both women with and without threatened PTL symptoms. They evaluated the test performance of placental α-macroglobulin-1 measurements in cervico-vaginal fluid regarding 3 different presentation-to-delivery intervals: less than or equal to 2, less than or equal to 7, less than or equal to 14 days. In addition, these researchers calculated placental α-macroglobulin-1 performance in combination with other prognostic factors such as US cervical length measurements. A total of 126 women were included in the study. The authors detected high specificity (97 % to 98 %) and NPV (89 % to 97 %) for placental α-macroglobulin-1 at all time-intervals. They assessed placental α-macroglobulin-1 in combination with cervical length measurements (less than or equal to 15 mm) in the sub-group of women presenting with threatened PTL symptoms (n = 63) and detected high PPVs (100 %) for 7- and 14-day presentation-to-delivery intervals. The authors concluded that the findings of this study provided evidence that placental α-macroglobulin-1 testing in cervico-vaginal fluid combined with cervical length measurements, accurately predicted PTB in women with PTL symptoms. They stated that this novel test combination may be used clinically to triage women presenting with threatened PTL, avoiding over-treatment and unnecessary hospitalizations. This was a relatively small, observational study; its findings need to be validated by well-designed studies.
Salivary Progesterone Test for Preterm Birth
Sharma and colleagues (2018) noted that there is currently no simple test available for screening all women at risk of spontaneous PTB in low income setting, although high resource settings routinely use cervical length measurement and cervico-vaginal fluid fetal fibronectin for identification and care of women at risk due to clinical history. In rural India, where the public health system has limited infra-structure, trained staff and equipment, there is a greater need to develop a low-cost screening approach for providing early referral, treatment and remedial support for pregnant women at risk of PTB. There is interest in the use of a salivary progesterone test as a screening tool. Preliminary evidence from India, Egypt and United Kingdom has shown promise for this type of test. The test requires further validation in a low resource community setting. The PROMISES study aims to validate and test the feasibility of introducing a low-cost salivary progesterone PTB prediction test in 2 rural districts in India with high rates of prematurity. It is a prospective study of 2,000 pregnant women recruited from Panna and Satna in Madhya Pradesh over approximately 24 months. Demographic and pregnancy outcome data will be collected, and pregnancies will be dated by US. Salivary progesterone will be measured by ELISA in samples obtained between 24 to 28 weeks of gestation. The association between salivary progesterone and PTB will be determined and the utility of salivary progesterone to predict preterm birth of les than 34, as well as less than 30 and less than 37 weeks assessed. Additional qualitative data will be obtained in terms of acceptability and feasibility of saliva progesterone testing and knowledge of PTB. The authors concluded that a validated cost-effective saliva test, which has potential for further adaptation to a “point of care” setting will allow early identification of pregnant women at risk of PTB, who could be linked to an effective pathway of care and support to reduce PTB and associated adverse consequences.
These researchers stated that the salivary progesterone test, if successful, will fill in the gap of providing a simple diagnostic tool for predicting PTB that can be easily adopted within the routine pregnancy/antenatal period at the level of community health workers and equip health system with an appropriate management plan for at-risk women for the rural settings. However, in tandem, it will require adequate US facilities in these areas and increased education of women so that they reveal pregnancy earlier and access US for accurate pregnancy dating. The future scale-up of the test, if successfully combined with accurate pregnancy dating, could lead to significant improvements in care for pregnant women and neonatal outcomes related to PTB.
Ashworth and colleagues (2021) noted that India has an overall neonatal mortality rate of 28/1,000 livebirths, with higher rates in rural India. Approximately 3.5 million pregnancies in India are affected by PTB annually and contribute to approximately 1/4 of PTBs globally. Embedded within the PROMISES study (which aims to validate a low-cost salivary progesterone test for early detection of PTB risk), these researchers presented a mixed methods explanatory sequential feasibility sub-study of the salivary progesterone test. A pre-training and post-training questionnaire to assess Accredited Social Health Activists (ASHAs) (n = 201) knowledge and experience of PTB and salivary progesterone sampling was analyzed using the McNemar test. Descriptive statistics for a cross-sectional survey of pregnant women (n = 400) were presented in which the acceptability of this test for pregnant women was assessed. Structured interviews were undertaken with ASHAs (n = 10) and pregnant women (n = 9), and were analyzed using thematic framework analysis to examine the barriers and facilitators influencing the use of this test in rural India. Before training, ASHAs' knowledge of PTB (including risk factors, causes, post-natal support and testing) was very limited. After the training program, there was a significant improvement in the ASHAs' knowledge of PTB. All 400 women reported the salivary test was acceptable with the majority finding it easy but not quick or better than drawing blood. For the qualitative aspects of the study, analysis of interview data with ASHAs and women, the thematic framework comprised of 3 main areas: implementation of intervention; networks of influence as well as access to healthcare. Qualitative data were stratified and presented as barriers and facilitators. The authors concluded that the findings of this study suggested support for ongoing investigations validating PTB testing using salivary progesterone in rural settings.
Cando et al (2022) noted that several biomarkers have been examined to predict spontaneous PTB, including salivary progesterone. However, due to limited studies, the use of this biomarker remains controversial. In a meta-analysis, these investigators examined the available evidence and determined the role of salivary progesterone as a potential biomarker for PTB. All studies reporting the levels of salivary progesterone among pregnant women with reported birth outcomes were obtained from Ovid Medline, Scopus, CINAHL, and Cochrane Central Register of Controlled Trials from inception to January 10, 2022. A review of titles and abstracts was carried out independently by 3 reviewers. The quality of the studies was evaluated using the Newcastle-Ottawa scale. Meta-analysis was carried out in R v.4.1.3 using the "meta" package. A total of 5 studies entailing 861 pregnant patients from Egypt, India, Iraq, and the U.S. were included in this meta-analysis. The random-effects model showed that salivary progesterone level after the 28th week of gestation was significantly different between patients with term and PTB (standardized mean difference [SMD]: 1.99; 95 % CI: 0.44 to 3.54) with a high degree of heterogeneity (I2 = 96 %, p < .001). Based on the results of this meta-analysis, women with term birth had higher level of salivary progesterone after the 28th week of gestation than those with PTB. The authors concluded that the findings of this study suggested that low salivary progesterone level after the 28th week of gestation was significantly associated with PTB. This study also highlighted the use of salivary samples for monitoring sex steroid hormones throughout pregnancy.
Mid-Trimester Amniotic Fluid Proteins and Spontaneous Preterm Delivery
Hallingstrom and colleagues (2020) noted that amniotic fluid is clinically accessible via amniocentesis and its protein composition may correspond to birth timing; thus, early changes in the amniotic fluid proteome could be associated with the subsequent development of spontaneous preterm delivery. These researchers carried out unbiased proteomics analysis of the association between mid-trimester amniotic fluid proteome and spontaneous preterm delivery and gestational duration, respectively. A secondary objective was to validate and replicate the findings by enzyme-linked immunosorbent assay (ELISA) using a 2nd independent cohort. Women undergoing a mid-trimester genetic amniocentesis at Sahlgrenska University Hospital/Ostra between September 2008 and September 2011 were enrolled in this study, designed in 3 analytical stages. First, an unbiased proteomic discovery phase using LC-MS analysis of 22 women with subsequent spontaneous preterm delivery (cases) and 37 women who delivered at term (controls). Second, a validation phase of proteins of interest identified in stage 1. Third, a replication phase of the proteins that passed validation using a second independent cohort consisting of 20 cases and 40 matched controls. A total of 9 proteins were nominally significantly associated with both spontaneous preterm delivery and gestational duration, after adjustment for gestational age at sampling, but none of the proteins was significant after correction for multiple testing. Several of these proteins have previously been described as being associated with spontaneous preterm delivery etiology and 6 of them were thus validated using ELISA. Two of the proteins passed validation; neutrophil gelatinase-associated lipocalin and plasminogen activator inhibitor 1, but the results could not be replicated in a second cohort. The authors concluded that neutrophil gelatinase-associated lipocalin and plasminogen activator inhibitor 1 are potential biomarkers of spontaneous preterm delivery and gestational duration but these findings could not be replicated. These researchers stated that further research is needed to determine the value of mid-trimester amniotic fluid proteins as potential predictive biomarkers of spontaneous preterm delivery and gestational duration.
The authors stated that drawbacks of this study were that the enrolled women may not reflect the general population as they were of a more advanced maternal age and have a higher risk of fetal chromosomal abnormalities than the overall population. However, mid-trimester amniotic fluid samples could only be collected in line with clear clinical indications, such as genetic testing, leaving few other opportunities to collect such samples. By excluding women with known or suspected fetal abnormalities from the study and women with confirmed anomalies from analysis, the bias that this introduced has partly been handled. Furthermore, only women who understood Swedish were enrolled. The rate of spontaneous preterm delivery rate differs between ethnicities, which can affect the generalization. The limitation of the control group to delivery between 38+0 and 41+6 gestational weeks was based on a case control design but is not optimal from the continuous perspective where gestational duration is studied. Finally, ELISA kits were considered unsuitable for the use of amniotic fluid for three potentially interesting candidates (SEMA A (V), IGFBP-5 and IGFBP-7) from the proteomics exploratory phase.
Furthermore, an UpToDate review on “Preterm labor: Clinical findings, diagnostic evaluation, and initial treatment” (Lockwood, 2020) does not mention testing of mid-trimester amniotic fluid proteome as a diagnostic option.
Combined Available Biomarkers and Cervical Length Measurement for Preterm Delivery
Dehaene and colleagues (2021) stated that an accurate prognostic method for PTB could avoid unnecessary treatment(s) with potentially negative effects. In a systematic review, these investigators examined the prognostic accuracy of commercially available bedside cervico-vaginal biomarker tests in combination with CL compared to CL measurement alone and/or a biomarker test alone, for PTB within 7 days after testing symptomatic women at 22 to 34 weeks. The Medline, Cochrane, Embase and Web of Science databases were searched from inception to August 28, 2019. A total of 708 articles were identified and screened using Rayyan. Studies reporting on the predictive accuracy of combined tests compared to CL or biomarker alone for the prediction of PTB within 7 days of testing in symptomatic women with intact membranes were included. A piloted data extraction form was used. Direct comparisons of the prognostic accuracy of the combination test with CL measurement or a biomarker alone were carried out, as well as comparisons of prognostic accuracy of the included combination tests (indirect comparisons). A total of 12 articles were included (7 on fFN, 4 on pIGFBP-1, 1 comparing both). A variety of CL cut-offs was reported. The results could not demonstrate superiority of a combination method compared to single methods. Th authors concluded that due to data scarcity and quality, the superiority of either predictive test for PTB, either combination or single, cannot be demonstrated with this systematic review. These researchers recommended further research to compare available biomarkers.
Metabolomic Biomarkers of Preterm Delivery
Ronde and colleagues (2021) noted that as the leading cause of peri-natal mortality and morbidity worldwide, the impact of premature delivery is undisputable. Thus far, non-invasive, cost-efficient and accurate biochemical markers to predict PTB are scarce. In a systematic review, these investigators examined the potential of non-invasive metabolomic biomarkers for the prediction of PTB. Databases were systematically searched from March 2019 up to May 2020 resulting in 4,062 articles, of which 45 were retrieved for full-text assessment. The resulting metabolites used for further analyses, such as ferritin, prostaglandin and different vitamins were obtained from different human anatomical compartments or sources (vaginal fluid, serum, urine and umbilical cord) and compared between groups of women with preterm and term delivery. None of the reported metabolites showed uniform results. These researchers stated that future research should focus on external validation of potential biomarkers in vaginal swabs and urine of pregnant women and examine a combination of the most promising ones.
Salivary Uric Acid
Puschl and colleagues (2020) stated that there remains a need for a non-invasive, low-cost and easily accessible way of identifying women at risk of developing hypertensive disorders in pregnancy. In a prospective, cohort, pilot study, these researchers examined the predictive value of longitudinal salivary uric acid measurement. Pregnant women (n = 137) from 20 weeks of gestation were recruited for this trial. Weekly samples of salivary uric acid were analyzed until delivery. Information regarding pregnancy and labor were obtained from the patient's record after delivery. Independent t-tests were used to compare mean levels of salivary uric acid in women with hypertensive complications and adverse fetal outcomes with women with normal pregnancies. Main outcome measures were pre-eclampsia, pregnancy-induced hypertension, spontaneous preterm delivery and small-for-gestational-age babies. From 21 weeks of gestation until delivery, levels of salivary uric acid increased significantly in women who subsequently developed pre-eclampsia and pregnancy-induced hypertension compared with women with normal pregnancies (pre-eclampsia -- mean at GA 21 to 24, 95 % CI: [mean GA21-24 ): 108 [63 to 185] versus 47 (39 to 55) µmol/L; p = 0.005; pregnancy-induced hypertension -- mean GA21-24 : 118 [54 to 258] versus 47 [39 to 55] µmol/L; p = 0.004). In women who had spontaneous preterm delivery, salivary uric acid levels increased significantly from 29 to 32 weeks of gestation compared with women with normal pregnancies (mean GA29-32 : 112 (57 to 221) versus 59 (50 to 71) µmol/L; p = 0.04). In women who had babies small-for-gestational-age of less than 10th percentile and small-for-gestational-age of less than 3rd percentile, differences in salivary uric acid levels were insignificant. The authors concluded that elevated levels of salivary uric acid preceded the onset of pre-eclampsia, pregnancy-induced hypertension and preterm delivery. These researchers stated that salivary uric acid may prove to be an early biomarker of hypertensive complications of pregnancy and spontaneous preterm delivery. They stated that these findings indicated proof-of-concept for potential use of salivary uric acid as a simple, low-cost predictive test for early detection of women at risk of pre-eclampsia, pregnancy-induced hypertension and spontaneous preterm delivery. Based on these findings, these researchers recommended further validation studies using updated technologies to measure and interpret salivary uric acid levels.
The authors stated that this study had several drawbacks that need to be addressed. Being a pilot study, the sample size was not very large. Prevalence of the outcomes in their population was low, as were the number of positive outcomes. This was reflected by the 95 % CI and standard errors, which were broader with respect to positive outcomes than to normal pregnancies. Furthermore, these investigators did not have information on possible influential factors on salivary uric acid levels such as obesity, smoking and chronic diseases. Obesity is a known risk factor of pre-eclampsia and studies have shown that salivary uric acid levels can be affected by obesity. This factor would need to be taken into account in a future clinical trial to tease out causal pathways and potential confounders. The data of the study had only become available for analysis in the last 2 years, which was why a significant period of time has passed since the data were collected. The results, however, remain novel and important given the continuing lack of a low-cost, easily accessible screening test for identifying women at risk of hypertensive complications of pregnancy and spontaneous preterm delivery.
Maternal Systemic Thiol/Disulphide Homeostasis for the Prediction of Pre-Term Birth
Cetin et al (2022) noted that spontaneous pre-term delivery is one of the major complications of pregnancy and the common cause of neonatal morbidity and mortality. Threatened pre-term labor (TPL) is also a frequent complaint in obstetric emergency care units worldwide. Triaging women with TPL is mandatory for planning further management therapies, since most of them will eventually deliver at term. Only the measurement of CL in symptomatic women has moderate accuracy in predicting pre-term delivery. Short cervix is described as an independent predictor of pre-term delivery in women with TPL, its predictive accuracy as a single measurement is relatively limited. On this account, several potential markers like fFN in the cervicovaginal fluid, salivary estriol, prolactin in vaginal discharge, maternal serum calponin and IL-6 in the amniotic fluid were examined to predict pre-term delivery in previous studies. However, none of them represented an excessive predictive accuracy like high sensitivity, PPV or NPV. In a prospective, pilot study, these researchers examined maternal systemic thiol/disulphide homeostasis (TDH) for the short-term prediction of PTB in women with TPL. This trial included 75 pregnant women whose pregnancies were complicated by TPL; 37 of them delivered within 7 days and 38 of them delivered beyond 7 days. Maternal serum samples were collected at the day of diagnosis and the TDH was measured. The maternal disulphide level was significantly higher in pregnant women who delivered within 7 days (25.0 ± 9.8 μmol/L versus 19.4 ± 9.8 μmol/L, p < 0.015). The threshold value of 22.1 μmol/L for maternal disulphide level predicted delivery within 7 days with 62.2 % sensitivity and 60.5 % specificity (AUC 0.651, CI: 0.53 to 0.78). The likelihood ratios for short cervix (25 mm or less) and maternal disulphide level (22 μmol/L or higher) to predict delivery within 7 days was found to be 8.7 and 7.3, respectively. The likelihood ratio of combining 2 tests to predict delivery within 7 days was found to be 11.4. The maternal TDH, which is an indicator of oxidative stress status in maternal compartment, was disturbed in TPL cases who delivered within 7 days. Elevated maternal disulphide level along with cervical length screening predicted a short latency period in pregnancies with TPL. These investigators reported a method that exhibited higher diagnostic and predictive performance in identifying TPL women with high risk of pre-term delivery. According to the current literature, there are accumulated data regarding the correlation between oxidative stress (OS) and pre-term delivery regardless of the amniotic membrane status. However, it is still debated whether OS is a trigger or a consequence of pre-term delivery. This study provided evidence for the 1st time that maternal serum thiol/disulphide homeostasis, which is an indicator of OS in maternal compartment, was disturbed in TPL cases who delivered within 7 days. The high disulphide level in maternal serum, along with CL measurement (short cervix) accurately predicted a short latency period in TPL cases. The authors concluded that this novel test combination (maternal serum disulphide level and CL measurement) could be used clinically to triage pregnant women presenting with TPL, avoiding over-treatment, unnecessary hospitalizations and increased medical costs. Future research will examine the reduction of maternal OS by using new antioxidant treatment strategies to improve peri-natal and long-term childhood outcomes.
Maternal Blood Biomarker for Prediction of Spontaneous Preterm Birth
Hornaday et al (2022) noted that the ability to predict sPTB before labor onset is a challenge, and to-date it is unclear which biomarker(s), may potentially predict sPTB, and whether their predictive power has any utility. These investigators carried out a systematic review to identify maternal blood biomarkers of sPTB. This study was carried out according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol for systematic reviews. A total of 4 databases (Medline, Embase, CINAHL, Scopus) were searched up to September 2021 using search terms: "preterm labor", "biomarker" and "blood OR serum OR plasma". Studies assessing blood biomarkers before labor onset against the outcome sPTB were eligible for inclusion. Risk of bias was assessed based on the Newcastle Ottawa scale. Increased odds of sPTB associated with maternal blood biomarkers, as reported by ORs, or predictive scores were synthesized. A total of 27 primary research articles met the inclusion criteria, reporting 278 unique markers significantly associated with and/or predictive of sPTB in at least 1 study. The most frequently examined biomarkers were those measured during maternal serum screen tests for aneuploidy, or inflammatory cytokines, although no single biomarker was clearly predictive of sPTB based on the synthesized evidence. Immune and signaling pathways were enriched within the set of biomarkers and both at the level of protein and gene expression. The authors concluded that there is currently no known predictive biomarker for sPTB. Inflammatory and immune biomarkers showed promise; however, positive reporting bias limited the utility of results. These researchers stated that the biomarkers identified may be more predictive in multi-marker models instead of as single predictors. Omics-style studies provided promising avenues for the identification of novel (and multiple) biomarkers. They stated that larger studies with adequate power and more consistent study design, namely, clearly defined outcomes that consider the heterogeneity and subtypes of PTB, are needed to identify a set of biomarkers predictive of sPTB.
Quantitative Fetal Fibronectin for Spontaneous Preterm Birth in Asymptomatic Pregnancies
Ruma et al (2023) stated that tests capable of accurate prediction of sPTB are crucial to inform clinical decisions to prevent neonatal deaths and reduce the risk of morbidity in surviving infants. In a systematic review and meta-analysis, these investigators examined the use of the quantitative fFN test to predict sPTB at different test concentration thresholds. They carried out literature searches in Medline, Embase, and the Cochrane Library in May 2022. Observational studies as well as clinical trials examining the clinical use of the quantitative fFN test in asymptomatic pregnancies before 37 weeks of gestation were eligible for inclusion. Meta-analysis quantified the risk of sPTB before 4 gestational age milestones (less than 28, less than 30, less than 34, and less than 37 weeks) based on quantitative fFN levels. No risk of bias assessment was performed; however, clinical and methodological heterogeneity was examined to determine the feasibility of performing analyses. A total of 11 studies showed a quantitative assessment of fFN can differentiate between very-high and very-low risks of sPTB in asymptomatic pregnancies with less than 10 % of women with very-low fFN (less than 10 ng/ml) versus 37 % to 67 % of women with very-high fFN (greater than 200 ng/ml) delivering before 34 weeks. A meta-analysis of 2 studies showed, albeit with a low number of events, the odds of sPTB before 28 weeks was 9 times higher in women testing positive at 50 ng/ml or higher, whereas the odds of sPTB was 25 times higher in women with fFN concentrations greater than 200 ng/ml (versus less than 50 ng/ml reference). Similarly, pooling 3 studies showed the odds of sPTB before 37 weeks was 4 times higher in women who tested positive at 50 ng/ml or higher whereas the odds of delivery before 37 weeks was 7 times higher for women with fFN concentrations 200 ng/ml or higher (versus less than 50 ng/ml reference). The authors concluded that quantitative fFN testing showed increased predictive capabilities and utility of fFN testing in clinical practice, potentially preventing unnecessary intervention for women at very low-risk and allowing an opportunity to optimize the management of asymptomatic patients at high-risk of preterm delivery.
Platelet-to-Lymphocyte Ratio and Serum High-Sensitivity C-Reactive Protein Levels and Adverse Pregnancy Outcomes in Women with Gestational Diabetes Mellitus
Tao et al (2023) noted that gestational diabetes mellitus (GDM) is a major complication of pregnancy. GDM is associated with a higher risk of adverse pregnancy outcomes (APO). These investigators examined the association between 3rd-trimester platelet-to-lymphocyte ratio (PLR) and high-sensitivity CRP (hsCRP) concentration and the risk of APO in GDM pregnant women. This study included 406 non-elderly GDM patients diagnosed in the Renmin Hospital of Wuhan University from May 2021 to February 2023 as the research objects. According to the presence or absence of APO, they were divided into an APO group (n = 171) and a non-APO group (n = 235). Logistic regression model to evaluate the correlation between PLR and hsCRP and APO in women with GDM; restricted cubic spline analyses was used to examine non-linear correlations between PLR or hsCRP and the risk of APO; ROC curve analysis of the diagnostic performance of PLR and hsCRP for APO in women with GDM. APO occurred in 171 (42.1 %) of the 406 included participants. Compared with the non-APO group, patients in the APO group had higher PLR and hsCRP levels. The incidence of APO was positively associated with PLR and the hsCRP level in each logistic regression model (p < 0.05). After adjusting for all the risk factors included in this study, restricted cubic spline analyses found that the PLR and the hsCRP level were positively associated with the risk of APO. The authors concluded that the levels of PLR and hsCRP in the 3rd trimester were related to the occurrence of APO in women with GDM, and high levels of PLR and hsCRP may indicate the higher risk of the occurrence of APO. Moreover, these researchers stated that if the association and related mechanisms between PLR and hsCRP with APO in patients with GDM are confirmed in future research, potential interventions to improve maternal and infant outcomes can be expected.
The authors stated that this study had 2 main drawbacks. First, due to the small sample size, other risk factors for APO were not stratified. Second, although these investigators found elevated levels of PLR and hsCRP in GDM pregnant women in the 3rd-trimester APO group, they were unable to collect any data on PLR and hsCRP levels in the disease during the 1st and 2nd trimesters. Blood samples obtained longitudinally during pregnancy may add more comprehensive data to understand the value of PLR and hsCRP levels during disease development.
Amniotic Fluid Sludge
Suff et al (2023) noted that PTB is the leading cause of global neonatal mortality. Amniotic fluid sludge, thought to indicate intra-amniotic infection, may have potential as a clinical biomarker of risk of PTB. In a retrospective cohort study, these researchers examined if the presence of amniotic fluid sludge in pregnant women with a known short cervical length could aid in improving the understanding of the etiology and guide management choice. They examined the effects of the presence of amniotic fluid sludge on the risk of PTB in high-risk asymptomatic pregnant women with a short cervical length (less than 25 mm) at a large tertiary referral maternity center. Amniotic fluid sludge was detected on a routine trans-vaginal US scan. A total of 147 pregnant women with a short cervical length were identified, 54 of whom had amniotic fluid sludge. Compared with pregnant women without amniotic fluid sludge, pregnant women with amniotic fluid sludge were more likely to have a short cervical length (19 mm versus 14 mm, respectively; p < 0.0001) and increased cervico-vaginal fFN concentrations at diagnosis (125 ng/ml versus 45 ng/ml, respectively; p = 0.0006). Pregnant subjects with amniotic fluid sludge were at increased risk of mid-trimester loss and delivery before 24 weeks of gestation (RR, 3.4; 95 % CI: 1.2 to 10.3). Additionally, this study showed that pregnant subjects with amniotic fluid sludge have increased cervico-vaginal IL-8 concentrations, supporting the concept of amniotic fluid sludge as an indicator of an inflammatory response to microbial invasion (p = o.03). Neonatal outcomes were similar between the 2 groups. The authors concluded that in this cohort of high-risk asymptomatic pregnant women with a short cervical length, the presence of amniotic fluid sludge was associated with an increased risk of delivery before 24 weeks of gestation. Moreover, pregnant women with amniotic fluid sludge were more likely to have increased fFN levels, and inflammatory cytokines, especially IL-8, in the cervico-vaginal fluid, supporting the concept that amniotic fluid sludge is associated with an infective or inflammatory process. Moreover, these investigators stated that future research should aim to further establish the clinical significance of amniotic fluid sludge presence and guide subsequent management.
Lipidomic Analysis of Cervico-Vaginal Fluid
Hong et al (2023) stated that CVF is an excellent specimen for monitoring PTB as it characterizes cervical metabolites, the vaginal environment, and specific host immune responses. However, extensive lipid analysis of CVF to explain PTB has not been studied. In this study, these researchers carried out a systematic analysis combining high-throughput lipid analysis and omics to discover the unique metabolic properties of the cervix. Liquid chromatography-high resolution mass spectrometry successfully detected a total of 190 lipids in the CVF of 30 PTB and 30 term birth (TB) pregnant women. The whole lipidomics dataset analyzed by combining multi-variate and uni-variate statistical analysis revealed 35 lipid biomarkers, including phospholipids and sphingolipids. Remarkably, sphingomyelin, which plays a physiologically essential role in sphingolipids, was significantly down-regulated in PTB. Metabolic pathway study provided a close relationship between vaginal microbial organization and cell membrane formation, further supporting the robustness of these findings. The authors concluded that sphingolipids and phospholipids, which were determined to be important lipids for predicting PTB in this trial, showed a high value of ROC curve of greater than 0.7, indicating that a lipid diagnostic test and understanding the mechanism of lipids is highly related to the vaginal microbiome. Thus, this finding has high potential as a predictor of PTB. These investigators noted that the findings of metabolic differences between ceramide and sphingomyelin, especially in sphingolipid biosynthesis and metabolism, providing novel and substantial contributions to the existing literature. They stated that future studies should clarify the contribution of the host and microbial communities to these metabolic changes and ultimately explain the physiological changes that resulted in metabolic differences in women with PTB. These researchers stated that investigation of CVF lipid metabolites has great potential for unraveling the mechanisms associated with TB and PTB.
Inflammatory Biomarkers for Preterm Premature Rupture of Membranes (PPROM) Pregnancies
In a retrospective, single-center study, Karabay et al (2024) examined the value of inflammatory indices in predicting the latency period until birth in patients with PPROM. This trial was carried out on PPROM cases between 24 and 34 weeks of gestation at Ankara Etlik City Hospital Perinatology Department from October 2023 to April 2024. A total of 146 subjects were divided into 2 groups: Group 1 included 73 patients who gave birth within 72 hours of PPROM diagnosis, and Group 2 included 73 patients who gave birth after 72 hours. This study examined the prognostic significance of various inflammatory markers neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR), monocyte/lymphocyte ratio (MLR), systemic immune inflammation index (SII), systemic inflammatory response index (SIRI), pan-immune inflammation value (PIV), immature granulocytes (IG), multi-inflammatory index (MII)-1, MII-2, and MII-3 in predicting the latency period in patients with PPROM. Only MII-1, MII-2, and MII-3 reliably predicted labor within 72 hours. The cut-off value for MII-1 was greater than 48.3, with a sensitivity of 57.7 % and specificity of 57.3 % (AUC: 0.598, 95 % CI: 0.503 to 0.692, p = 0.042). For MII-2, the cut-off was greater than 1,037.6, with a sensitivity of 57.7 % and specificity of 57.3 % (AUC: 0.611, 95 % CI: 0.516 to 0.705, p = 0.021). MII-3 had a cut-off of greater than 10,919.9, with a sensitivity of 53.5 % and specificity of 52 % (AUC: 0.595, 95 % CI: 0.501 to 0.690, p = 0.046). The authors concluded that these findings showed that, among NLR, PLR, MLR, SII, SIRI, PIV, IG, MII-1, MII-2, and MII-3, only MII-1, MII-2, and MII-3 levels were statistically significant in predicting birth timing. These researchers stated that incorporating these inflammatory markers into clinical practice could improve prenatal management, enhance patient counseling, and optimize resource allocation. Moreover, these investigators stated that further research with larger cohorts is needed to validate these findings and confirm their clinical utility.
The authors stated that this study had 2 main drawbacks. First, since this trial included single-center and single-population data, the generalizability of these findings to different groups may be limited. To increase the reliability and validity of these findings, further studies involving larger patient cohorts and different populations are needed. Second, due to its retrospective nature, unknown confounding factors may not have been included. Future studies could improve sensitivity and specificity values by including factors related to PPROM etiology in expanded prediction models.
Cytokine Levels (e.g., Interleukins) and Preterm Birth
In a nested, case-control study, Grandi et al (2024) examined a panel of cytokines and placental insufficiency with the risk of pre-term delivery (PTD). A total of 82 mother-infant-placenta pairs were selected at 20+0 to 25+6 weeks. Circulating biomarker levels were carried out using Luminex flowmetric xMAP technology. Cytokines classified as Th1, Th2 or Th17 and other biomarkers were selected. The ratio between birth-weight and placental-weight (BW/PW) was used as a proxy for placental efficiency. Spearman correlation, univariate analyses and logistic regression models were calculated. Sensitivity, specificity, positive and negative likelihood ratios were calculated using the ROC curve. Mean GA was 250 days, 14.6 % were small for gestational age (SGA), 4.8 % large for gestational age (LGA), and 13.4 % stunted. Placental efficiency was higher for term newborns (p < 0,001), and 18/22 (81 %) preterm biomarker values were higher than the control group. Th1 cytokines were highly correlated, while the weakest correlation was observed in other biomarkers. Less education was associated with a higher risk of PTD (p = 0.046), while there was no appreciable difference in the risk of PTD for placental insufficiency. Biomarkers showed negligible adjusted OR of PTD (0.90 to 1.02). IL-6, IL-8, IL-1β, TNFβ, IL-4, IL-13, GCSF, MIP1A, VEGF, EGF, and FGF2 presented a higher sensitivity ranging from 75.56 % to 91.11 %. The authors concluded that IL-8, IL-12p40, IL-4, IL-13, GCSF, MIP1B, and GMSF in asymptomatic pregnant women were associated with PTD. These researchers stated that these findings suggested an activation of maternal inflammatory response.
These investigators stated that normal cut-off values for the cytokines are not available in the literature for direct comparison with the outcome (prematurity). The small sampling could explain the lack of association, mainly because of an under-powered study, with a wide CI. These researchers noted that several biomarkers in maternal and fetal compartments have been mechanistically linked to PTD; however, none of them was a reliable predictor of pregnancy outcome. They stated that additional follow-up monitoring is needed to examine if the association found in this study would persist into early childhood and beyond and may aid in predicting future long-term disorders (e.g., failure to thrive, neurodevelopmental disabilities, metabolic syndrome, as well as cardiovascular diseases).
PreTRM for Prediction of Preterm Birth
Saade et al (2016) stated that preterm delivery remains the leading cause of peri-natal mortality. Risk factors and biomarkers have traditionally failed to identify the majority of preterm deliveries. These researchers developed and validated a mass spectrometry-based serum test to predict spontaneous preterm delivery (sPTD) in asymptomatic pregnant women. A total of 5,501 pregnant women were enrolled between 17(0/7) and 28(6/7) weeks gestational age in the prospective Proteomic Assessment of Preterm Risk Trial at 11 sites in the U.S. between 2011 and 2013. Maternal blood was collected at enrollment and outcomes collected following delivery. Maternal serum was processed by a proteomic work-flow, and proteins were quantified by multiple reaction monitoring mass spectrometry. The discovery and verification process identified 2 serum proteins, insulin-like growth factor-binding protein 4 (IBP4) and sex hormone-binding globulin (SHBG), as predictors of spontaneous preterm delivery. These investigators examined a predictor using the log ratio of the measures of IBP4 and SHBG (IBP4/SHBG) in a clinical validation study to classify spontaneous preterm delivery cases (less than 37(0/7) weeks gestational age) in a nested case-control cohort different from subjects used in discovery and verification. Strict blinding and independent statistical analyses were employed. The predictor had an area under the receiver operating characteristic curve (AUROC) value of 0.75 and sensitivity and specificity of 0.75 and 0.74, respectively. The IBP4/SHBG predictor at this sensitivity and specificity had an odds ratio (OR) of 5.04 for spontaneous preterm delivery. Accuracy of the IBP4/SHBG predictor increased using earlier case-versus-control gestational age cutoffs (e.g., less than 35(0/7) versus 35 or more(0/7) weeks gestational age). More importantly, higher-risk subjects defined by the IBP4/SHBG predictor score generally gave birth earlier than lower-risk subjects. The authors concluded that a pre-defined predictive test for sPTD based on serum measurements of IBP4 and SHBG in asymptomatic parous and nulliparous women was validated in a completely independent set of subjects. Moreover, these researchers stated that further functional studies on these proteins, their gene regulation, and related pathways may help to elucidate the molecular and physiological underpinnings of sPTD. Application of this predictor should enable early and sensitive detection of women at risk of sPTD. This early detection may improve pregnancy outcomes through increased clinical surveillance as well as accelerate the development of clinical interventions for PTD prevention.
The authors stated that this study had several drawbacks. First, universal TVUS measurement of cervical length (CL) was not carried out routinely at the majority of the study centers and was available for fewer than 1/3 of study subjects. It would be of interest to examine if CL measurements would improve upon the proteomic predictor in future studies or, alternatively, if risk stratification by the IBP4/SHBG classifier would identify women who would benefit most from serial CL measurements. Second, there was an insufficient number of women with prior preterm delivery who were not being treated with progesterone to allow inclusion of this variable in the analysis; thus, women with prior sPTD should be treated according to national guidelines, which include prophylactic treatment with 17-alpha hydroxyprogesterone caproate. Third, owing to sample size limitations, a more complete assessment of confounders will require future studies. Fourth, it will be intriguing to examine the performance of the molecular predictor together with a body mass index variable or perhaps in combination with other medical/pregnancy history and sociodemographic characteristics.
Grabner et al (2021) noted that PTB carries increased risk of short- and long-term health problems as well as higher healthcare costs. Current strategies using clinically accepted maternal risk factors (prior PTB, short cervix) could only identify a minority of singleton PTBs. These researchers modeled the cost-effectiveness of a risk-screening-and-treat strategy versus usual care for commercially insured pregnant U.S. women without clinically accepted PTB risk factors. The risk-screening-and-treat strategy included use of a novel PTB prognostic blood test (PreTRM) in the 19th to 20th week of pregnancy, followed by treatment with a combined regimen of multi-component high-intensity-case-management and pharmacologic interventions for the remainder of the pregnancy for women assessed as higher-risk by the test, and usual care in women without higher risk. They built a cost-effectiveness model using a combined decision-tree/Markov approach and a U.S. payer perspective. These investigators modeled 1-week cycles of pregnancy from week 19 to birth (preterm or term) and assessed costs throughout the pregnancy, and further to 12-months post-delivery in mothers and 30-months in infants. PTB rates and costs were based on more than 40,000 mothers and infants from the HealthCore Integrated Research Database with birth events in 2016. Estimates of test performance, treatment effectiveness, and other model inputs were derived from published literature. In the base case, the risk-screening-and-treat strategy dominated usual care with an estimated 870 fewer PTBs (20 % reduction) and $54 million less in total cost ($863 net savings per pregnant woman). Reductions were projected for neonatal intensive care admissions (10 %), overall length-of-stay (LOS) (7 %), and births of less than 32 weeks (33 %). Treatment effectiveness had the strongest influence on cost-effectiveness estimates. The risk-screening-and-treat strategy remained dominant in the majority of probabilistic sensitivity analysis simulations and model scenarios. The authors concluded that the use of a novel prognostic test during pregnancy to identify women at risk of PTB combined with evidence-based treatment was estimated to reduce total costs while preventing PTBs and their consequences. (It should be noted that study funding was provided by Sera Prognostics Inc., the maker of the PreTRM test, to HealthCore Inc).
The authors stated that the drawbacks of the study included reliance on treatment effectiveness estimates from published studies of multi-component high-intensity case management (HICM), progesterone, and novel bundled regimens in an evolving field. The interaction between effectiveness of this treatment and the population in which it would be used was dynamic, and to-date the effectiveness of progesterone has primarily been studied in women identified as high-risk using other prognostic methods, such as before PTB or short cervix. While the PreTRM test would be applied to a population of otherwise low-risk women, the resulting treatment would only be targeted at those identified as higher-risk by the test, i.e., a population where the treatment strategy is likely effective based on previous literature in other high-risk women. These investigators did not model adverse events (AEs) related to the risk-screening-and-test strategy; they noted that safety evidence for progesterone is long-standing and reassuring. In light of the recent FDA proposal to withdraw the leading brand of injectable progesterone from the U.S. market, this health economic model focused on the vaginal formulations. Other treatments (e.g., cerclage, antibiotics, and vitamin D) were not modelled and the conclusions from this model may not extend to their use. Furthermore, this model had typical limitations common to the use of medical claims data, which lacked clinical context and were subject to potential coding, billing, and recording errors as well as other inconsistencies. These researchers did not model neonatal mortality as an isolated outcome; across the entire PTB population neonatal mortality is uncommon. Births of less than 23 weeks’ gestation, still-birth, or abortion were also not modeled. They occurred very rarely in this sample and were not known to be affected by the treatment. Patients without health insurance or those who were covered solely under public programs (e.g., Medicaid) were not part of the analyzed population; commercially insured individuals were more likely to be currently employed and tend to have many factors that put them at lower risk than the remaining population, such as lower rates of smoking or sexually transmitted diseases (STDs). While the authors were unable to reliably ascertain race for the patients included in this data-set, it was also likely that fewer mothers were Black, Hispanic, or of other racial and ethnic minorities, compared to national statistics. In 2018, 63 % of births to white mothers were covered by commercial insurance, versus 28 % of births to Black mothers. Childbirth is an area of healthcare with especially high disparities by race and economic status; consequently, the potential benefits of risk identification and treatment for patients under-represented in the commercially insured population is an important area for future research. Finally, it is important to note the limitations of these researchers’ focus on direct healthcare cost. They did not consider quality of life (QOL) (for mothers or infants) or long-term clinical sequelae, productivity, or other indirect costs, all of which may be substantially impacted by PTB. This was a conservative assumption likely to under-estimate benefit of the risk-screening-and-treat strategy. These investigators stated that generating and incorporating appropriate data in this population would be an important task for future research.
Burchard et al (2022) noted that the clinical management of pregnancy and spontaneous PTB (sPTB) relies on estimates of GA. In a retrospective study, these investigators examined the effect of GA dating uncertainty on the observed performance of a validated proteomic biomarker risk predictor, and tested the generalizability of that effect in a broader range of GA at blood draw. In a secondary analysis of a prospective clinical trial, these researchers compared 2 GA dating categories: both US and dating by last menstrual period (LMP) (all subjects) and excluding dating by LMP (excluding LMP). The risk predictor's performance was observed at the validated risk predictor threshold both in weeks 191/7-206/7 and extended to weeks 180/7-206/7. Strict blinding and independent statistical analyses were employed. The validated biomarker risk predictor showed greater observed sensitivity of 88 % at 75 % specificity (increases of 17 % and 1 %) in more reliably dated (excluding-LMP) subjects, relative to all subjects. Excluding dating by LMP significantly improved the sensitivity in weeks 191/7-206/7. In the broader blood draw window, the previously validated risk predictor threshold significantly stratified higher and lower risk of sPTB, and the risk predictor again showed significantly greater observed sensitivity in excluding-LMP subjects. The authors concluded that the improved estimation of the performance of an sPTB risk predictor in subjects whose GA at delivery was more certain suggested that the risk predictor provided accurate predictions that were confirmed by better dating. Improvements in risk prediction could result in better risk stratification, and this work suggested that more well-designed controlled studies on interventions to reduce risk are needed and have the potential to have significant impacts.
The authors stated that the drawbacks of this trial included the modest size of the study and the availability of only one GA dating method per subject. furthermore, the exact GA of the dating US was not available in the PAPR study. For this reason, these researchers established biomarker performance among a more precisely dated population by excluding LMP-only dating. These investigators stated that future studies are planned to extend these analyses in clinical trials where the gestational age of the dating US is available and within-patient comparison of gestational age dating methods can be performed. Lasty, this study was a retrospective analysis, which could be enhanced by focused prospective studies.
Hoffman et al (2024) stated that screening clinically low-risk singleton pregnancies with a validated maternal blood test for PTB risk, then providing preventive treatments for those at higher risk, will improve neonatal outcomes compared to a large historical population. The AVERT PRETERM trial took place from June 2018 to September 2020 at ChristianaCare Hospital (Newark, DE). Women with singleton non-anomalous pregnancies and no PTB history were prospectively enrolled, screened at 191/7-206/7 weeks gestation with a maternal circulating biomarker test for sPTB risk, and followed through neonatal hospital discharge. Those identified at higher risk (16.0 % or higher, approximately twice the U.S. population risk) were offered vaginal progesterone (200 mg) and aspirin (81 mg) daily, and care management comprising increased patient outreach and education. Outcomes were compared for prospective arm participants who screened either “not-higher-risk” or “higher-risk accepting treatment” (modified intent-to-treat [ITT] population) with those in a ChristianaCare historical arm of 10,000 pregnancies. Co-primary outcomes were: neonatal morbidity and mortality, as measured by a composite neonatal morbidity index (NMI) score integrating medical complications with neonatal intensive care unit (NICU) LOS or death; and neonatal hospital LOS (NNLOS). Cox proportional hazards survival analysis and ordinal logistic regression were used to evaluate outcomes and control for differences between arms. A COVID-prompted research shut-down occurred when 1,460 biomarker-screened individuals had reached 37 weeks’ gestation in a racially diverse prospective arm. Of these, 34.7 % (507/1,460) had biomarker scores indicating higher risk, with 56.4 % (286/507) accepting intervention and 43.6 % (221/507) declining. The remaining 65.3 % (953/1,460) were designated not-higher-risk. Prospective arm neonates had lower NMI scores (OR, 0.81, 95 % CI: 0.67 to 0.98, p = 0.031), and severe neonatal morbidity (NMI 3 or higher) was reduced by 18 % compared to historical controls. Neonatal hospital LOS also were shorter (HR, 1.35, 95 % CI: 1.08 to 1.70, p = 0.01), with average NNLOS decreasing by 21 % in a quantile of longest stays. The authors concluded that improved neonatal outcomes after biomarker PTB risk stratification and preventive care management for higher-risk individuals suggested a test-and-treatment strategy that could ameliorate PTB complications and associated medical, societal and economic burdens in a previously unidentifiable patient population: singleton, often nulliparous, pregnancies deemed clinically low-risk. (It should be noted that some of the authors had competing interests -- BS, JS, and MGW were paid consultants of Sera Prognostics, Inc. For the purposes of this study, JS and MGW reported to MKH and were paid consultants of ChristianaCare; and BS was supported by Sera Prognostics, Inc. MKH received an investigator-initiated grant from Sera Prognostics, Inc., to conduct this study).
The authors stated that this study had several limitations. First, imbalances inherent in comparison of a prospective arm with a historical arm that differed in several maternal demographic and medical conditions. These differences were addressed via multi-variable modeling but remain a potential source of bias. Even so, significant demographic differences in the prospective versus historical arm -- older age, more hypertension and more smoking -- likely biased the prospective arm toward increased PTB incidence, further underscoring the importance of these findings. Second, for low-dose aspirin (LDASA), guideline changes have expanded the number of women eligible for treatment. A recent estimate suggested that most pregnant women should be counseled regarding LDASA. One may argue that both progesterone and care management have limited evidence of effectiveness in the situations studied; however, the multi-factorial etiologies of PTB made proving that either or both were effective in a broad range of individuals difficult, as an intervention may work on some etiologies but not others. Third, the value of using this suite of interventions with clinically low-risk pregnancies, at least in theory and perhaps supported by results herein, is the potential for broader coverage of etiologies and better hope of success through multiple interventions. Fourth, there is overlap among trial outcomes, as NICULOS was included in the NMI index, and no multiple comparison adjustment of “p values” was made for co-secondary and exploratory outcomes.
Combs et al (2023) examined if pregnancy is prolonged by the use of a proteomics-based maternal serum screening test followed by treatment interventions. This was a post-hoc, secondary analysis of the PREVENT-PTB randomized trial comparing screening with the PreTRM test versus no screening. The primary trial analysis found no significant between-group difference in the PTB rate. Rather than considering a dichotomous outcome (preterm versus term), these researchers treated GA at birth as a continuous variable using survival analysis. They also evaluated between-group difference in NICU LOS and duration of respiratory support. Results indicated that pregnancy was significantly prolonged in subjects screened with the PreTRM test compared to controls (adjusted HR 0.53, 95 % CI: 0.36 to 0.78, p < 0.01). Newborns of screened subjects had significantly shorter NICU stays but no significant decrease in duration of respiratory support. In the PreTRM screen-positive group, interventions that were associated with pregnancy prolongation included care management and low-dose aspirin but not 17-hydroxyprogesterone caproate. The authors concluded that screening with the PreTRM test followed by interventions for screen-positive pregnancies may prolong pregnancy and reduce NICU LOS; however, future research is needed to confirm these observations and to evaluate the individual contributions of care management, low-dose aspirin, and perhaps other interventions in achieving these apparent benefits.
The authors stated that this study had several limitations. First, this was a post-hoc, secondary analysis performed after the primary analysis was reported. Second, the number of PTB cases was small because of the early termination of the trial. Third, these investigators did not have data on the use of antenatal corticosteroids, which could have impacted preterm neonatal respiratory morbidity. Fourth, the specific treatments chosen in response to the PreTRM test were based on patient preferences, not randomization; therefore, the analysis of treatments showed only associations and not necessarily a causal link between treatments and outcomes. Lastly, these researchers did not use any statistical corrections to adjust for the large number of hypotheses tested; therefore, the probability of type 1 statistical error was larger than the nominal 5 %.
These investigators stated that given the limitations, they considered these findings to be exploratory only, suggesting potential topics for future trials. They suggested that there is a need for large, prospective studies to examine the effectiveness of specific interventions such as care management and low-dose aspirin in patients identified at increased risk for PTB by the PreTRM test; and ongoing trials may provide additional insights.
In a prospective, randomized study, Branch et al (2023) examined if a program of mid-trimester serum proteomics screening of women at low-risk for sPTB and the use of a PTB risk-reduction protocol in those whose results indicated an increased risk of sPTB would reduce the likelihood of sPTB and its sequelae. Prospective comparison of birth outcomes in singleton pregnancies with mid-trimester CL of 2.5 cm or greater and at otherwise low-risk for sPTB were randomized to undergo or not undergo mid-trimester serum proteomics screening for increased risk of sPTB. Screen-positive women were offered a group of interventions aimed at reducing the risk of spontaneous PTB. The primary outcome was the rate of sPTB of less than 37 weeks, and secondary outcomes were GA at delivery, total neonatal LOS, and NICU LOS. Unscreened and screen-negative women received standard care. The adaptive study design targeted a sample size of 3,000 to 10,000 women to detect a reduction in sPTB from 6.4 % to 4.7 %. Due to limited resources, the trial was stopped early before data unblinding. A total of 1,191 women were randomized; screened and unscreened women were demographically similar. sPTB of less than 37 weeks occurred in 2.7 % of screened women and 3.5 % of controls (p = 0.41). In the screened compared with the unscreened group, there were no between-group differences in the GA at delivery, total neonatal LOS, and NICU LOS. However, the NICU LOS among infants admitted for sPTB was significantly shorter (median = 6.8 days, inter-quartile range [IQR]: 1.8 to 8.0 versus 45.5 days, IQR: 34.6 to 79.0; p = 0.005). The authors concluded that mid-trimester serum proteomics screening of women at low risk for sPTB and the use of a sPTB risk-reduction protocol in screen-positive patients did not significantly reduce the rate of sPTB compared with women not screened, though the trial was under-powered; therefore, limiting the interpretation of negative findings. Infants in the screened group had a significantly shorter NICU LOS, a difference likely due to a reduced number of infants in the screened group that delivered less than 35 weeks. These researchers stated that the findings of a shortened NICU LOS following sPTB in the screened group were important exploratory outcomes that should prompt further study.
The authors stated that this trial had several drawbacks. First, it was prematurely terminated because of inadequate funding. Second, the rate of sPTB was just over 3 %, much less than the expected 6.4 % rate they used in designing the study. Third, even though these investigators observed a statistical difference in the NICU LOS among neonates admitted after sPTB, they did not adjust for multiple comparisons of all analyses performed; thus, results should be interpreted with caution. Finally, these findings may not be generalizable to the general U.S. population because the study population lacked ethnic diversity and over 75 % of participants had commercial insurance.
Furthermore, an UpToDate review on “Spontaneous preterm birth: Overview of risk factors and prognosis” (Robinson and Norwitz, 2024) states that “A test (PreTRM Test) for two serum proteins, insulin-like growth factor-binding protein 4 and sex hormone-binding globulin, is available for clinical use to predict PTB. In a study to develop and validate a mass spectrometry-based serum test to predict sPTB in asymptomatic pregnant people, the test had sensitivity and specificity of 0.75 and 0.74, respectively, for predicting PTB < 37 weeks. We recommend not moving forward with serum screening for PTB until such screening has been adequately tested and validated”.
Measurement of Maternal Serum Alpha-1 Antitrypsin Levels for Prediction of Spontaneous Preterm Birth
Tissarinen et al (2024) stated that currently there are no accurate means to predict spontaneous PTB (sPTB). Recently, these investigators observed low expression of alpha-1 antitrypsin (AAT) in sPTB placentas. These researchers compared the concentrations of maternal serum AAT in pregnancies with preterm and term deliveries. Serum CRP was used as a reference inflammatory marker. Two populations were studied. The 1st population comprised women who eventually experienced birth spontaneously (sPTB group) or term (control group). The 2nd population included pregnant women shortly before delivery and non-pregnant women. These investigators observed that serum AAT levels were higher in the sPTB group than in the controls, and a similar difference was observed when serum CRP was considered in multi-variable analysis; however, the overlap in the AAT concentrations was considerable. No statistical significance was observed in serum AAT levels between preterm and term pregnancies at delivery; however, AAT levels were higher at delivery compared to non-pregnant controls. These researchers did not observe a strong correlation between serum AAT and CRP in early pregnancy samples and at labor. The authors proposed that during early pregnancy, complicated by subsequent sPTB, modest elevation of serum AAT was associated with sPTB. Moreover, these researchers stated that further investigations are needed to understand the causes and consequences of the maternal-placental-fetal interaction of AAT and its relationship to premature birth.
The authors stated that this study had several drawbacks. First, the lack of clinical data, as this study relied on the available information in birth diaries. For example, in study population 1, there was no information regarding possible maternal infection at the time of outpatient visit for pregnancy-based population screening. However, these investigators examined if other available, possible confounding factors are associated with serum AAT levels. In study population 1, the authors observed that smoking during pregnancy and in-vitro fertilization (IVF) were more common among women who gave birth prematurely. Smoking did not associate with serum level of AAT in this population of pregnant women, which aligned with previous result from a population of non-pregnant participants. Similarly, these investigators observed that AAT levels did not differ between those who received IVF treatments and those who did not. Furthermore, CL measurements were not available in birth diaries. Short CL, besides history of PTB, is one of the predictors of sPTB; however, routine screening for short cervix was not recommended in present population. The sample size during the 2nd half of pregnancy was limited and remained to be studied in the future. The sPTB group likely over-represented a history of previous PTBs, as the previously reported study focused on mothers having more than 1 sPTB.
Measurement of Plasma Levels of Arginine for Prediction of Spontaneous Preterm Birth
Akhter et al (2024) stated that PTB is a leading cause of infant mortality and morbidity. The pathogenesis of PTB is complex and involves many factors, including socio-economy, inflammation and infection. Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are involved in labor as inhibitors of nitric oxide, a known relaxant of the uterine smooth muscles. Arginines are scarcely studied in relation to PTB and these investigators examined plasma levels of arginines (ADMA, SDMA and L-arginine) in women with spontaneous PTB and term birth. The study was based on data from the population-based, prospective cohort BASIC study conducted in Uppsala County, Sweden, between September 2009 and November 2018. Arginines were analyzed by ultra-high performance liquid chromatography (ultra-HPLC) using plasma samples taken at the onset of labor from women with spontaneous PTB (n = 34) and term birth (n = 45). These investigators also analyzed the inflammation markers CRP, TNF receptors (TNF-R1 and TNF-R2), and growth differentiation factor 15 (GDF-15). Women with spontaneous PTB had higher plasma levels of ADMA (p < 0.001), and L-Arginine (p = 0.03). Furthermore, inflammation marker, TNF-R1 (p = 0.01) was higher in spontaneous PTB compared to term birth. Additionally, in spontaneous PTB, no significant correlations could be observed when comparing levels of arginines with inflammation markers, except ADMA versus CRP. The authors concluded that the findings of this study provided novel evidence for the potential involvement of arginines in the pathogenesis of spontaneous PTB and it appeared that arginine levels at labor vary independently of several inflammatory markers. Moreover, these researchers stated that further investigations are needed to examine the potential of arginines as therapeutic targets in the prevention and management of spontaneous PTB.
The authors stated that the main drawback of this trial was that, because of the cross-sectional nature of the study, it was not possible to conclude the causality between the studied biomarkers and sPTB. These researchers stated that future studies that measure arginines and inflammation markers in PTB patients, for example at several time-points in pregnancy, at labor, and post-partum, would provide more insight into the potential causality of arginines in PTB.
Measurement of Vaginal Immuno-Proteome for Prediction of Spontaneous Preterm Birth
Shaffer et al (2024) noted that PTB is the leading cause of neonatal morbidity and mortality globally. Most cases of PTB occur spontaneously and result from PTL with intact (spontaneous PTL [sPTL]) or ruptured (PPROM) membranes. The prediction of sPTB remains under-powered due to its syndromic nature and the dearth of independent analyses of the vaginal host immune response. These researchers carried out the largest longitudinal investigation targeting vaginal immune mediators, referred to herein as the immune-proteome, in a population at high-risk for sPTB. Vaginal swabs were collected across gestation from pregnant women who ultimately underwent term birth, sPTL, or PPROM. Cytokines, chemokines, growth factors, and anti-microbial peptides in the samples were quantified via specific and sensitive immunoassays. Predictive models were constructed from immune mediator concentrations. Throughout uncomplicated gestation, the vaginal immune-proteome harbors a cytokine network with a homeostatic profile. Yet, the vaginal immune-proteome is skewed toward a pro-inflammatory state in pregnant women who ultimately experience sPTL and PPROM. Such an inflammatory profile includes increased monocyte chemo-attractants, cytokines indicative of macrophage and T-cell activation, as well as reduced anti-microbial proteins/peptides. The vaginal immune-proteome has improved predictive value over maternal characteristics alone for identifying women at risk for early (less than 34 weeks) sPTB. The authors concluded that vaginal immune-proteome undergoes homeostatic changes throughout gestation and deviations from this shift were associated with sPTB. In addition, the vaginal immune-proteome could be leveraged as a potential biomarker for early sPTB, a subset of sPTB associated with extremely adverse neonatal outcomes.
The authors stated that a major drawback of this study was that, despite the comprehensive survey of the vaginal immune-proteome, the identification of causal mechanisms driving the changes in specific mediators associated with different subsets of PTB is yet to be elucidated. The incorporation of microbiome and other omics, as well as mechanistic approaches requiring the use of animal models, was outside the scope of the research question investigated herein. Yet, these researchers considered that the substantial data generated in this study, together with their predictive models, can serve to spark new researches focused on targeting key mediators and their relationships with local immune-microbiome interactions in the context of pregnancy complications. Finally, the population included in this study was primarily composed of African-American women. These researchers stated that further investigations are needed to ascertain the generalizability of these findings to other populations.
References
The above policy is based on the following references:
- Akhter T, Hedeland M, Bergquist J, et al. Elevated plasma levels of arginines during labor among women with spontaneous preterm birth: A prospective cohort study. Am J Reprod Immunol. 2024;91(6):e13889.
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