Value of fetal fibronectin as a predictor of preterm delivery for a low-risk population

Preterm labor with intact membranes: a simple noninvasive method to identify patients at risk for intra-amniotic infection and/or inflammation

OBJECTIVE

To develop a noninvasive scoring system to identify patients at high risk for intra-amniotic infection and/or inflammation, which would reduce the need for amniocentesis.

METHODS

This prospective cohort study comprised patients admitted with preterm labor and intact membranes (20-34 weeks of gestation) who underwent a transabdominal amniocentesis and for whom concentrations of quantitative cervical fetal fibronectin and of maternal serum C-reactive protein (CRP) were determined. Intra-amniotic infection was defined as a positive amniotic fluid culture for microorganisms. Intra-amniotic inflammation was defined as an amniotic fluid matrix metalloproteinase-8 concentration >23 ng/mL. Multivariate logistic regression analysis was performed to identify intra-amniotic infection/inflammtion with noninvasive parameters that had a significant relationship with univariate analysis. With four parameters identified by multivariate analysis, we generated a noninvasive risk scoring system.

RESULTS

Of the study population consisting of 138 singleton pregnant women, (1) the overall rate of intra-amniotic infection/inflammation was 28.3% (39/138); (2) four parameters were used to develop a noninvasive risk scoring system [i.e. cervical fetal fibronectin concentration (score 0-2), maternal serum CRP concentration (score 0-2), cervical dilatation (score 0-2), and gestational age at presentation (score 0-1)]; the total score ranges from 0 to 7; 3) the area under the curve of the risk score was 0.96 (95% confidence interval (CI), 0.92-0.99), significantly higher than that of each predictor in the identification of intra-amniotic infection/inflammation (p < .001, for all); 4) the risk score with a cutoff of 4 had a sensitivity of 94.9% (37/39), a specificity of 90.9% (90/99), a positive predictive value of 80.4% (37/46), a negative predictive value of 97.8% (90/92), a positive likelihood ratio of 10.4 (95% CI, 5.6-19.5), and a negative likelihood ratio of 0.06 (95% CI, 0.15-0.22) in the identification of intra-amniotic infection/inflammation.

CONCLUSIONS

(1) The combination of four parameters (concentrations of cervical fetal fibronectin and maternal serum CRP, cervical dilatation, and gestational age) was independently associated with intra-amniotic infection and/or inflammation; and (2) the risk scoring system comprised of the combination of 4 noninvasive parameters was sensitive and specific to identify the patients at risk for intra-amniotic infection and/or inflammation.

Biomarkers for Preterm Delivery

Preterm birth occurring before the thirty-seventh gestational week complicates 4.5%-18% of pregnancies worldwide. The pathogenesis of spontaneous preterm delivery is not fully understood. Among the factors held to be responsible for its pathogenesis, the most emphasized is the inflammatory process. Studies in terms of the prediction of preterm delivery are basically divided into 3 categories: 1) Prediction in pregnant women who are asymptomatic and without risk factors, 2) Prediction in pregnant women who are asymptomatic and have risk factors, 3) Prediction in symptomatic pregnant women who have threatened preterm labour. In this chapter, the topic of biomarkers in relation to preterm delivery is discussed. The most commonly used markers in published studies are fetal fibronectin, cervical pIGFBP-1 and cervical length measurement by transvaginal ultrasound. For prediction in symptomatic pregnant women applying to the hospital with threatened preterm labour, the markers used are fetal fibronection, insulin-like growth factors (IGFs) and inflammatory markers. Preterm labour prediction with markers checked in the first and second trimesters are fetal fibronection, insulin-like growth factors (IGFs), micro RNAs, progesterone, circulating microparticles (CMPs), inflammatory markers, matrix metalloproteinases, aneuploidy syndrome screening test parameters and other hormones.

Increasing the Prediction Power of Preterm Labor using Interleukin 6 and Fetal Fibronectin as Alarming Signals in Symptomatic Patients

Background: Giving birth at preterm is considered as a bothering problem to both healthcare systems and pregnant women around the world, causing alarming levels of mortality. To avoid this issue, certain biological markers can be employed for early detection to predict the occurrence of the PTD (PTD) ahead of time for giving better medical care to the pregnant women who at risk of PTD. Objective: The current study was performed to evaluate the power of using interleukin-6 (IL-6) and fetal fibronectin (fFN) present in the cervicovaginal fluid (CVF) as predictors of the symptomatic PTD patients. Patients & Methods: In this study, 91 pregnant hospital attendees (24-34 weeks; 18-45 years old) with suggested PTD symptoms, such as abdominal pain and uterine contraction and with cervical length of less than 25mm, were participated. To detect IL-6 and fFN, vaginal swabs were collected for performing an ELISA test to later follow up with the patients within 48hrs, seven days, and 14 days from the first day of admission to the hospital.  Results: No significant association between PTD with patients age, parity, BMI, and gestational age, but significant association with previous history of PTD. There was significant association between PTD and increase the level of CVF fFN and IL-6 with best cut-off value for CVF fFN is(>45ng/ml) with (95%CI of 0.763-0.918) and accuracy of 85.2% with a sensitivity of 73.1% and specificity of 95.6% which is of high significant value (P≤0.01).While CVF of IL-6 (>231pg/ml) with (95% CI of 0.630- 0.820), with accuracy of 73.3%,  sensitivity of 50% and specificity of 96.9% which was statistically significant finding (P≤0.01).The predictive value of combined fFN and IL-6  in women at risk  of preterm labor was 84.6% with sensitivity 84.6%,specificity 92.3%, positive predictive value (PPV) 81.5%, negative predictive value (PPV) 93.8% and accuracy of 90.1%. Conclusion:  Each of fFN or IL-6 located in the CVF may provide a strong predictor of PTD; however, this prediction capability may provide an even stronger signal of detecting PTD ahead of time if both biomarkers requested at the same time.

Evaluation of the effectiveness of foetal fibronectin as a predictor of preterm birth in symptomatic preterm labour women

BACKGROUND

The prediction of preterm birth (PTB) is important in the management of symptomatic preterm labour women. We evaluated the effectiveness of the foetal fibronectin (fFN) test for predicting PTB in symptomatic preterm labour women with consideration of physiologic changes in cervical length (CL) during pregnancy.

METHODS

This prospective study included 85 women with symptomatic preterm labour of a singleton pregnancy. Positive fFN was defined as a fFN level of > 50 ng/mL in cervicovaginal secretion, while a short CL was defined as that below 25th percentile at the corresponding gestational age. We evaluated effectiveness of the fFN test, CL, and the combination of these two tests, including sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), positive likelihood ratio (LR⁺), negative likelihood ratio (LR^-) to predict the PTB within 7 and 14 days of testing and PTB at < 34 and 37 weeks of gestation. We also present the odds ratios (ORs) of the test results, defining the women with both negative results as the reference group.

RESULTS

Of the 85 women, 31 (36.5%) showed a positive fFN and 44 (51.8%) had a short CL. PTB occurred within 7 and 14 days of testing and before 34 and 37 weeks of gestation in 17.6, 20.0, 23.5 and 49.4% of the women, respectively. The fFN and CL results showed low predictive effectiveness for the studied outcomes with LR⁺ (fFN, 1.5-1.9; CL, 1.0-1.5) and LR^- (fFN, 0.7; CL, 0.7-0.9). The combined use of fFN and CL could not improve these results (LR⁺, 1.4-2.3; LR^-, 0.7-0.9). However, the risk of PTB before 37 weeks was increased in women with positive fFN but not CL shortening compared to the reference group (odds ratio [OR], 3.8; 95% confidence interval [CI], 1.1-1.3). The risk of PTB before 34 weeks was increased in both positive fFN and CL compared to the reference group (OR, 8.1; 95% CI, 1.9-34.5).

CONCLUSION

Although, our approach could not improve the ability to predict PTB, it could identify women at risk for delivery before 34 or 37 weeks of gestation. Therefore, it could be used to manage women with symptomatic preterm labour.

A high concentration of fetal fibronectin in cervical secretions increases the risk of intra-amniotic infection and inflammation in patients with preterm labor and intact membranes

Objective To determine whether the risk of intra-amniotic infection/inflammation and spontaneous preterm delivery (SPTD) varies as a function of the concentration of cervical fetal fibronectin (fFN) in patients with preterm labor and intact membranes. Methods This prospective study included 180 patients with preterm labor and intact membranes who had a sample collected for quantitative fFN measurement and underwent amniocentesis. Amniotic fluid was cultured for aerobic and anaerobic bacteria and genital mycoplasmas. Intra-amniotic inflammation was defined as an amniotic fluid matrix metalloproteinase-8 concentration >23 ng/mL. Results (1) The prevalence of intra-amniotic infection/inflammation and SPTD within 7 days was 32.2% (58/180) and 33.9% (61/178), respectively; (2) The higher the fFN concentration, the greater the risk of intra-amniotic infection/inflammation and SPTD within 7 days (P<0.001, respectively); (3) An fFN concentration 150 ng/mL had a better diagnostic performance than an fFN 50 ng/mL in the identification of intra-amniotic infection/inflammation and SPTD within 7 days; (4) Among the patients with an fFN <50 ng/mL, intra-amniotic infection/inflammation was identified in 7.6% (6/79) of patients and 66.7% (4/6) delivered within 7 days. Conclusion The higher the concentration of fFN, the greater the risk of intra-amniotic infection/inflammation and SPTD in patients with preterm labor and intact membranes.

The fetal fibronectin test: 25 years after its development, what is the evidence regarding its clinical utility? A systematic review and meta-analysis

Background: The identification of women at risk for preterm birth should allow interventions which could improve neonatal outcome. Fetal fibronectin, a glycoprotein which acts normally as glue between decidua and amniotic membranes could be a good marker of impending labour when its concentration in cervicovaginal secretions between 22 and 36 weeks of gestation is ≥50 ng/mL. Many authors worldwide have tested this marker with many different methodologies and clinical settings, but conclusions about its clinical use are mixed. It is time for a comprehensive update through a systematic review and meta-analysis.Methods: We searched PubMed, Cochrane Library, and Embase, supplemented by manual search of bibliographies of known primary and review articles, international conference papers, and contact with experts from 1-1990 to 2-2018. We have selected all type of studies involving fetal fibronectin test accuracy for preterm delivery. Two authors independently extracted data about study characteristics and quality from identified publications. Contingency tables were constructed. Reference standards were preterm delivery before 37, 36, 35, 34, and 32 weeks, within 28, 21, 14, or 7 d and within 48 h. Data were pooled to produce summary likelihood ratios for positive and negative tests results.Results: One hundred and ninety-three primary studies were identified allowing analysis of 53 subgroups. In all settings, none of the summary likelihood ratios were >10 or <0.1, thus indicating moderate prediction, particularly in asymptomatic women and in multiple gestations.Conclusions: The fetal fibronectin test should not be used as a screening test for asymptomatic women. For high-risk asymptomatic women, and especially for women with multiple pregnancies, the performance of the fetal fibronectin test was also too low to be clinically relevant. Consensual use as a diagnostic tool for women with suspected preterm labor, the best use policy probably still depends on local contingencies, future cost-effectiveness analysis, and comparison with other more recent available biochemical markers.

Predictive Accuracy of Serial Transvaginal Cervical Lengths and Quantitative Vaginal Fetal Fibronectin Levels for Spontaneous Preterm Birth Among Nulliparous Women

Importance

Spontaneous preterm birth is a leading cause of infant mortality. Prediction, largely based on prior pregnancy outcomes, is not possible in women pregnant for the first time.

Objective

To assess the accuracy of universal screening to predict spontaneous preterm birth in nulliparous women using serial measurements of vaginal fetal fibronectin levels and cervical length.

Design, Settings, and Participants

A prospective observational cohort study of nulliparous women with singleton pregnancies, from 8 clinical sites across the United States between October 2010 and May 2014. Women and clinicians were blinded to results unless cervical shortening less than 15 mm was identified.

Exposures

Transvaginal cervical length and quantitative vaginal fetal fibronectin levels were reviewed at 2 study visits 4 or more weeks apart.

Main Outcomes and Measures

Spontaneous preterm birth at less than 37 weeks was the primary outcome. Cervical length and quantitative fetal fibronectin were considered independently and together at each visit. Measurement distributions were compared for spontaneous preterm birth vs all other births. Spontaneous preterm birth before 32 weeks was a secondary outcome.

Results

The study included 9410 women (median age, 27.0 [interquartile range, 9.0] years; 60.7% non-Hispanic white, 13.8% non-Hispanic black, 16.5% Hispanic, 4.0% Asian, and 5.1% other), of whom 474 (5.0%) had spontaneous preterm births, 335 (3.6%) had medically indicated preterm births, and 8601 (91.4%) had term births. Among women with spontaneous preterm birth, cervical length of 25 mm or less occurred in 35 of 439 (8.0%) at 16 to 22 weeks' gestation and in 94 of 403 (23.3%) at 22 to 30 weeks' gestation. Fetal fibronectin levels of 50 ng/mL or greater at 16 to 22 weeks identified 30 of 410 women (7.3%) with spontaneous preterm birth and 31 of 384 (8.1%) at 22 to 30 weeks. The area under the receiver operating characteristic curve for screening between 22 and 30 weeks for fetal fibronectin level alone was 0.59 (95% CI, 0.56-0.62), for transvaginal cervical length alone was 0.67 (95% CI, 0.64-0.70), and for the combination as continuous variables was 0.67 (95% CI, 0.64-0.70).

Conclusions and Relevance

Among nulliparous women with singleton pregnancies, quantitative vaginal fetal fibronectin and serial transvaginal ultrasound cervical length had low predictive accuracy for spontaneous preterm birth. These findings do not support routine use of these tests in such women.

Vaginal progesterone vs. cervical cerclage for the prevention of preterm birth in women with a sonographic short cervix, previous preterm birth, and singleton gestation: a systematic review and indirect comparison metaanalysis

OBJECTIVE

No randomized controlled trial has compared vaginal progesterone and cervical cerclage directly for the prevention of preterm birth in women with a sonographic short cervix in the mid trimester, singleton gestation, and previous spontaneous preterm birth. We performed an indirect comparison of vaginal progesterone vs cerclage using placebo/no cerclage as the common comparator.

STUDY DESIGN

Adjusted indirect metaanalysis of randomized controlled trials.

RESULTS

Four studies that evaluated vaginal progesterone vs placebo (158 patients) and 5 studies that evaluated cerclage vs no cerclage (504 patients) were included. Both interventions were associated with a statistically significant reduction in the risk of preterm birth at <32 weeks of gestation and composite perinatal morbidity and mortality compared with placebo/no cerclage. Adjusted indirect metaanalyses did not show statistically significant differences between vaginal progesterone and cerclage in the reduction of preterm birth or adverse perinatal outcomes.

CONCLUSION

Based on state-of-the-art methods for indirect comparisons, either vaginal progesterone or cerclage are equally efficacious in the prevention of preterm birth in women with a sonographic short cervix in the mid trimester, singleton gestation, and previous preterm birth. Selection of the optimal treatment needs to consider adverse events, cost and patient/clinician preferences.

Fetal fibronectin as a predictor of preterm birth

Preterm delivery remains the leading cause of perinatal mortality and occurs in approximately 7-9% of pregnancies. The main problem for the obstetrician is the inability to detect women at risk from this complication. The presence of fetal fibronectin (fFN) in cervicovaginal secretions has been proposed as a specific predictor of preterm delivery. Immunohistochemical studies suggest that fFN is present in the extracellular matrix of the decidua basalis next to the intervillus space. It has been studied intensively in symptomatic patients and has a positive predictive value of 43-79%. It has also a negative predictive value of 99.7% for birth within 7 days and 93% for delivery before 37 weeks. Similarly, in high-risk asymptomatic women, it has been proved a useful screening tool for the prediction of preterm delivery, yielding a sensitivity of 43-92%, a specificity of 52-93%, a positive predictive value of 43-85% and a negative predictive value of 86-99%. In low-risk asymptomatic women, fFN has a sensitivity of 63-73%, a specificity of 80-98%, a positive predictive value of 13-36% and a negative predictive value of 95-97%. In women presenting with preterm contractions, a negative test may make one withhold potentially dangerous tocolytic therapy. In asymptomatic women this test can identify patients who have a very high risk for early delivery. Women identified as being high-risk can be offered steroid injections in order to improve lung maturity in preterm babies. Additionally, they can be counselled about the signs and symptoms of preterm labour, so that they can seek medical advice before labour is actually established. However, extensive research is still needed, as no clear benefit in preventing preterm birth using this test, has been shown so far.

Assessment of the impact of introducing fetal fibronectin assay in the management of preterm labour at Middlemore Hospital, New Zealand

Elevated levels of fetal fibronectin (fFN) in cervicovaginal secretions beyond 20-22 weeks of gestation are used as a predictor of preterm birth in patients with corroborative symptoms and signs.

AIM

To assess the impact of introducing the fFN assay on the diagnosis, length of hospital stay and cost of managing patients presenting with symptoms of premature labour in our hospital.

METHODS

The first 30 fFN-tested patients (fFN group) were prospectively recruited and followed up until delivery. Hospital stay and management costs (costs of individual tests and treatment administered) and neonatal outcomes were compared with 30 matching historical controls.

RESULTS

Overall management costs of the fFN-group were comparable with controls (NZ dollar 918 versus NZ dollar 943 per patient, p = 0.44). The fFN-group had a trend towards reduced length of hospital stay (p = 0.082), less tocolysis (p = 0.002) and use of steroids (p < 0.001). The cost of managing an fFN-positive patient was more than an fFN-negative patient, but not statistically significant (NZ dollar 1117 versus NZ dollar 846, respectively, p = 0.11).

CONCLUSION

Despite a trend towards reduced hospital stay and less use of obstetric intervention, total expenditure in patient management has not reduced with the availability of the fFN assay in our hospital. This may only reflect the slow introduction of a new policy that with time may be implemented to full effect.

"Blind" vaginal fetal fibronectin as a predictor of spontaneous preterm delivery

OBJECTIVE

To assess the accuracy of vaginal fetal fibronectin sampling without use of a sterile speculum examination as a screening test for predicting spontaneous preterm birth.

METHODS

A historical cohort of patients who were followed up with serial fetal fibronectin testing between 1998 and 2001 was identified. All patients were considered to be at high risk for preterm delivery and were screened with fetal fibronectin testing without using a speculum at 2- to 3-week intervals from 22 weeks to 32 weeks of gestation. Charts were reviewed for fetal fibronectin results and pregnancy outcome data. Groups were compared using chi(2) analysis or Fisher exact test with significance defined as P < .05.

RESULTS

A total of 1,396 fetal fibronectin tests from 416 pregnancies were performed via the "blind" sampling technique. Overall, 24.9% of pregnancies delivered spontaneously before 37 weeks; 9.1% delivered spontaneously before 34 weeks. For delivery before 34 weeks of gestation, the test had a sensitivity of 44.7%, a specificity of 88.4%, a positive predictive value of 27.9%, and a negative predictive value of 94.1%. For delivery within 14 and 21 days of a single fetal fibronectin assessment, the test had a sensitivity of 52% and 45.5%, a specificity of 94.5% and 94.9%, a positive predictive value of 14.6% and 22.5%, and a negative predictive value of 99.1% and 98.2%, respectively.

CONCLUSION

"Blind" vaginal fetal fibronectin sampling has high negative predictive values and specificities in predicting spontaneous preterm birth.

LEVEL OF EVIDENCE

II-2.

Primary predictors of preterm labour

Spontaneous preterm birth accounts for 60% of all preterm births in developed countries. With the increase in multiple pregnancies, induced preterm birth and the progress in neonatal care for extremely preterm neonates, spontaneous preterm birth for singleton pregnancies in developed countries has probably decreased over the past 30 years. This decrease is likely to be related to better prenatal care for all pregnant women because the recognition of primary risk factors in early or late pregnancy remains a basic part of prenatal care. The failure to distinguish between induced and spontaneous preterm labour in most population-based studies makes it difficult to interpret results with respect to the primary predictors of preterm labour. Many such primary predictors of preterm labour have been used over the past 20-30 years. These include individual factors, socio-economic factors, working conditions and obstetric and gynaecological history. Risk scores have been proposed in order to produce these data. Unfortunately, the predictive value of these scores, especially their specificity, is poor, mainly because all of these factors are indirect. We still cannot identify the mechanisms that lead to preterm labour and birth. New markers more directly related to preterm labour have recently been proposed, some of which relate to direct causes of preterm labour such as cervical ultrasound measurement, fetal fibronectin (FFN), salivary estriol, serum CRH and bacterial vaginosis. Several of these have predictive values, which are potentially useful for clinical practice. Nonetheless, pregnant women in developed countries are already closely monitored throughout pregnancy. Before proposing new screening tests to be applied systematically to all pregnant women, their advantages and drawbacks must be fully evaluated.

Vaginal fetal fibronectin as a predictor of spontaneous preterm delivery after multifetal pregnancy reduction

OBJECTIVE

The study was undertaken to assess the validity of vaginal fetal fibronectin assay as a screening test for spontaneous preterm delivery in asymptomatic patients who have undergone multifetal pregnancy reduction (MFPR).

STUDY DESIGN

A historic cohort of 63 patients who underwent MFPR between 10 and 14 weeks of gestation was identified. All patients underwent serial vaginal fetal fibronectin sampling every 2 to 3 weeks from 22 weeks of gestation until delivery or 32 weeks of gestation. The fetal fibronectin concentration was measured by enzyme-linked immunosorbent assay, with 50 ng/mL or greater indicating a positive result. Charts were reviewed for fetal fibronectin results and pregnancy outcome data. Groups were compared by use of Fisher exact test.

RESULTS

There were 13 singleton and 50 twin gestations after MFPR. A median of 4 fetal fibronectin assays were performed per patient. A total of 234 fetal fibronectin assays were performed with 222 (94.9%) negative results and 12 (5.1%) positive results. Overall, 41.3% of gestations were delivered spontaneously before 37 weeks; 7.9% were delivered before 34 weeks. The mean interval between tests was 17.8 days (+/-7.2 days). For delivery within 2 and 3 weeks of a single test, fetal fibronectin had a sensitivity of 66.7% and 50%, a specificity of 95.7% and 96.1%, a positive predictive value of 16.7% and 25%, and a negative predictive value of 99.5% and 98.6%, respectively.

CONCLUSION

The fetal fibronectin test has similar validity to predict spontaneous preterm delivery in these high-risk pregnancies as in previously published cohorts.

Vaginal fetal fibronectin as a predictor of spontaneous preterm delivery in the patient with cervical cerclage

OBJECTIVE

The purpose of this study was to assess the validity of vaginal fetal fibronectin as a screening test for spontaneous preterm birth in patients with cervical cerclage.

STUDY DESIGN

A historic cohort of 117 patients who underwent cervical cerclage placement between 1996 and 2002 were identified. All patients were followed up in a maternal-fetal medicine faculty practice in a university setting. Serial fetal fibronectin samples of vaginal secretions were collected every 2 to 3 weeks, starting at 22 weeks of gestation and continuing until 32 weeks or delivery, whichever came first.

RESULTS

There were 81 singleton, 23 twin, 12 triplet, and 1 quadruplet pregnancies. There were 61 ultrasound-indicated, 47 prophylactic, and 9 emergency cerclages that were placed. Most cerclages were of the modified Shirodkar type (95%) with a median gestational age at cerclage placement of 16.6 weeks. Overall, 33.3% of gestations were delivered spontaneously before 37 weeks of gestation; 17.1% of gestations were delivered spontaneously before 34 weeks. For deliveries within 2 weeks and 3 weeks of a single fetal fibronectin assessment, the test had a sensitivity of 50% and 48.3%, a specificity of 90% and 91.1%, a positive predictive value of 16.3% and 28.6%, and a negative predictive value of 97.9% and 96%, respectively. Subgroup analysis by number of fetuses (singleton, twin, and higher order multiple gestations) revealed similar values. For delivery before 34 weeks of gestation, fetal fibronectin had a sensitivity of 50%, a specificity of 78.4%, a positive predictive value of 33.3%, and a negative predictive value of 88%.

CONCLUSION

This study is the first to evaluate the use of vaginal fetal fibronectin assessments to screen for preterm birth in patients who had undergone cervical cerclage procedures. We conclude that this test has similar validity to predict spontaneous preterm delivery in these high-risk pregnancies, as in previously published cohorts.

Biochemical predictors of preterm labor: fetal fibronectin and salivary estriol

Preterm birth is a major complication of pregnancy and remains a leading cause of neonatal morbidity and mortality worldwide. Improvements in the authors' understanding of the pathophysiology of preterm labor have led to the development of novel diagnostic tools of use to identify women at greatest risk for preterm birth. Currently two FDA-approved biochemical tests are available in the United States: (1) fetal fibronectin and (2) salivary estriol. The presence of a positive fetal fibronectin test in the midtrimester of pregnancy is strongly associated with early spontaneous preterm birth. In contrast, a positive salivary estriol test is associated with late preterm birth, thus limiting its clinical use. Both tests have low test sensitivity and are currently used clinically for their negative predictive values. That is, women who screen negative are at very low risk for preterm birth and, thus, no interventions are indicated to prevent preterm birth. Women with a positive test are at increased risk and would be candidates for intervention. One of the main limitations of fetal fibronectin and salivary estriol, and an array of other proposed markers, is the fact that while these markers may aid in identification of women at increased risk for preterm birth, the authors currently have no clearly effective obstetric interventions for preterm-birth prevention in these high-risk women. Use of tocolytics, antimicrobials, or progesterone therapy currently has limited or unproven benefit in the management of women deemed at increased risk using these markers. Thus, until effective targeted obstetric interventions are available, the use of biochemical markers to identify women at increase risk for preterm birth remains largely research tools.

Biochemical markers for the prediction of spontaneous pre-term birth

OBJECTIVES

The aim of this study was to identify predictive biochemical markers for preterm labor.

METHODS

In this prospective study we included 225 asymptomatic Caucasian women consecutively enrolled at 24 weeks of gestation. The following data were collected only once at 24 weeks of gestation: vaginal pH, vaginal fFN, cervical and serum concentration of IL-6, IL-8 and TNFalpha, maternal blood serum, ferritin. Student's t-test, the chi(2)-test and multiple linear regression were used as statistical methods.

RESULTS

There were no differences between the age of patients, parity and gestational age at sampling between women who delivered at term and those who delivered pre-term (<37 weeks' gestation). There was a significant increase of cervical IL-6 (pre-term 608+/-1595 pg/l vs. at term 58.9+/-112 pg/l) and serum ferritin (pre-term microg/l 74.4+/-1.1 vs. at term 26.3+/-56.5 microg/l) in pregnant women who delivered pre-term (P<0.05). No differences in cervical IL-8 and cervical TNFalpha between pre-term and term deliveries were found. Multiple linear regression confirmed that the vaginal pH value and cervical fFN test were the best predictive biochemical markers of pre-term birth (standardized coefficient Beta=0.33 and 0.22, respectively).

CONCLUSIONS

In order to evaluate pregnancies for pre-term labor, the presence of pH>4.5 and a positive fFN test seems to be predictive of subsequent pre-term delivery.

Accuracy of cervicovaginal fetal fibronectin test in predicting risk of spontaneous preterm birth: systematic review

OBJECTIVE

To determine the accuracy with which a cervicovaginal fetal fibronectin test predicts spontaneous preterm birth in women with or without symptoms of preterm labour.

DESIGN

Systematic quantitative review of studies of test accuracy.

DATA SOURCES

Medline, Embase, PASCAL, Biosis, Cochrane Library, Medion, National Research Register, SCISEARCH, conference papers, manual searching of bibliographies of known primary and review articles, and contact with experts and manufacturer.

STUDY SELECTION

Two reviewers independently selected and extracted data on study characteristics, quality, and accuracy.

DATA EXTRACTION

Accuracy data were used to form 2x2 contingency tables with spontaneous preterm birth before 34 and 37 weeks' gestation and birth within 7-10 days of testing (for symptomatic pregnant women) as reference standards. Data were pooled to produce summary receiver operating characteristic curves and summary likelihood ratios for positive and negative test results.

DATA SYNTHESIS

64 primary articles were identified, consisting of 28 studies in asymptomatic women and 40 in symptomatic women, with a total of 26 876 women. Among asymptomatic women the best summary likelihood ratio for positive results was 4.01 (95% confidence interval 2.93 to 5.49) for predicting birth before 34 weeks' gestation, with corresponding summary likelihood ratio for negative results of 0.78 (0.72 to 0.84). Among symptomatic women the best summary likelihood ratio for positive results was 5.42 (4.36 to 6.74) for predicting birth within 7-10 days of testing, with corresponding ratio for negative results of 0.25 (0.20 to 0.31).

CONCLUSION

Cervicovaginal fetal fibronectin test is most accurate in predicting spontaneous preterm birth within 7-10 days of testing among women with symptoms of threatened preterm birth before advanced cervical dilatation.

Use of fetal fibronectin in women at risk for preterm delivery

Fetal fibronectin, a large molecular weight glycoprotein produced in the chorion, is expressed in cervical and vaginal secretions in women with disruption of the choriodecidual [table: see text] junction by labor or by inflammation. The presence of FFN in vaginal or cervical secretions before 35 weeks is a moderately good predictor of preterm delivery. The absence of FFN is a strong predictor that preterm delivery is unlikely within the next 7 to 14 days, with NPVs exceeding 99% in some studies. The predictive power of FFN is stronger at earlier gestation ages (24-28 wks) than it is later [table: see text] in pregnancy and is stronger for short-term prediction (7-14 d) than for predicting overall outcome (however, it remains statistically significant for predicting delivery < 37 wks). Although use of FFN in the clinical setting may require some changes to common protocols (e.g., performing sterile speculum examination before digital cervical examination), the use of FFN in patients with suspected preterm labor appears to have significant utility in reducing unnecessary interventions in women with symptoms suggestive of preterm labor. In women without symptoms, the use of FFN may be most beneficial in providing reassurance to some women thought to be at high-risk for preterm delivery because of past obstetric history. Screening women without symptoms at low-risk with FFN is not yet recommended because effective interventions are not demonstrated for patients found to be positive.

The effect of fetal fibronectin testing on admissions to a tertiary maternal-fetal medicine unit and cost savings

OBJECTIVE

Fetal fibronectin bedside testing has been proposed as a diagnostic tool for the accurate diagnosis of preterm labor. The study objective was to determine whether the introduction of routine fetal fibronectin bedside testing affected costs and transfer rates from referral district hospitals to a tertiary obstetric hospital, as well as direct admissions to a tertiary referral hospital.

STUDY DESIGN

We performed an 18-month prospective audit of fetal fibronectin use in 9 referral hospitals and one university maternal-fetal medicine unit. Data collected were delivery details and cervical dilatation at admission. Cost savings in terms of transport costs for patients with a negative fetal fibronectin result who were not transferred or admitted to the tertiary center were calculated for interhospital transfer (road ambulance or fixed-wing retrieval).

RESULTS

One hundred fifty-one patients had a presumptive diagnosis of threatened preterm labor. Forty-five patients had a positive fetal fibronectin result and 106 had a negative fetal fibronectin result (3 with cervical dilatation >/=3 cm). Eleven (24%) patients with a positive fetal fibronectin result were delivered within 7 days, and 5 (5%) with a negative fetal fibronectin result were delivered within 7 days. One patient was delivered at 34 weeks, and the remaining patients were delivered at or after 36 weeks' gestation. All 3 patients with negative fetal fibronectin results with cervical dilatation of >/=3 cm were delivered within 5 days, leaving 2 (1.9%) patients (with closed cervices and negative fetal fibronectin results) being delivered 5 days after the fetal fibronectin testing. Ninety percent of the patients admitted to a referral hospital with threatened preterm labor who had a negative fetal fibronectin result were not transferred; thus an unnecessary transfer was avoided, with cost savings ranging from $30,297 for road and fixed-wing transport.

CONCLUSION

A negative fetal fibronectin result is not helpful if cervical dilatation is present, and these patients should be treated as having a high risk of preterm delivery. The use of a fetal fibronectin test was associated with a 90% reduction in maternal transfer and can substantially reduce the costs and inconvenience associated with unnecessary transfer.

Markers of risk for preterm delivery

Clinical and experimental evidence indicate that PTD results from four primary pathogenic mechanisms: activation of the maternal or fetal HPA axis; amniochorionic-decidual or systemic inflammation; decidual hemorrhage; and, pathologic distention of the myometrium. Each of these four pathways has a distinct epidemiological and clinical profile, and unique biochemical and biophysical pathways initiating parturition, but shares a common final biochemical pathway involving myometrial activation and stimulation, and enhanced genital tract protease activity promoting PPROM and cervical change. Traditional methods of predicting women at risk relying on obstetrical history or symptoms and epidemiological risk factors are neither sensitive nor specific. Recent approaches to predicting PTD, including sonographic measurement of cervical length and biochemical assays for hCG, cytokines, fFN, MMPs, estrogens, and CRH, are more sensitive than traditional methods. Moreover, given the heterogeneous, interactive etiopathogeneses of PTD, multiple biochemical markers should not only increase sensitivity and specificity, but also permit the detection of the relative contribution of each pathogenesis to the overall risk of PTD.

Cervicovaginal fetal fibronectin as a marker for preterm delivery: a meta-analysis

OBJECTIVE

We performed a meta-analysis to determine the value of cervicovaginal fetal fibronectin as a marker for preterm delivery.

STUDY DESIGN

Selection criteria confined the analysis to original, English-language reports of prospective studies including women at <37 weeks' gestation with intact amniotic membranes. For the outcomes of delivery at <37 or <34 weeks' gestation or delivery within 7, 14, 21, or 28 days after fibronectin sampling, we calculated sensitivity and specificity rates for each study, for subgroups of studies, and for all studies combined.

RESULTS

A total of 27 studies met our inclusion criteria. For the outcomes of delivery at <37 and <34 weeks' gestation, overall sensitivity rates were 56% and 61% and overall specificity rates were 84% and 83%, respectively. For the outcomes of delivery within 7, 14, 21, and 28 days, we calculated sensitivity rates of 76%, 68%, 61%, and 43% and specificity rates of 88%, 89%, 91%, and 93%, respectively. For the subgroup of patients with symptoms of preterm labor, sensitivity rates for delivery within 7, 14, 21, and 28 days of 89%, 78%, 76%, and 71% and specificity rates of 86%, 86%, 88%, and 83%, respectively, were calculated.

CONCLUSION

Among patients with symptoms of preterm labor, cervicovaginal fetal fibronectin appears to be among the most effective predictors of preterm delivery.

Preterm labour: recent advances in understanding of pathophysiology, diagnosis and management

Recent advances in the importance of sociodemographic factors, including maternal stress, as well as potential predictors of preterm birth are reviewed. The recommended role of adjunctive antibiotic therapy, in women with preterm premature rupture of the membranes but not in women with intact membranes, is discussed. The possibility of causes other than those related to infection in preterm rupture of the membranes is raised, and new information regarding the use of glucocorticoids and tocolytics is presented. Despite steady improvements in neonatal survival and morbidity rates over the past decade primarily as a result of improved neonatal care, there has been no corresponding decrease in the incidence of preterm birth. An improved understanding of the pathophysiology and diagnosis of preterm birth remains one of the greatest challenges in obstetric care in this decade.

Prediction of preterm labour in multiple pregnancies

Various methods of predicting preterm labour in both singleton and multiple pregnancies have been studied including risk scoring systems, home uterine activity monitoring, cervical assessment and biochemical methods. In practice, risk scoring systems for preterm delivery perform poorly. Consensus in the literature regarding the usefulness of home uterine activity monitoring is lacking and well designed randomized controlled trials are required. Transvaginal ultrasound assessment of the cervix appears to have a role to play in the prediction of preterm labour. The presence of IFN in cervicovaginal fluid in the late second and early third trimesters is an important risk factor for preterm labour in asymptomatic women with multiple pregnancies. Preterm labour may be mediated in part by inflammatory cytokines. The measurement of these inflammatory cytokines in cervical secretions may also prove helpful in the prediction of preterm labour. It is anticipated that an improved ability to predict preterm labour in both singleton and multiple pregnancies will depend on increasing understanding of the condition's pathophysiology.

Use of fetal fibronectin in clinical practice

Preterm delivery remains a worldwide problem hindered by many unknowns, not the least of which is an inability to detect patients at risk for this complication of pregnancy. A unique form of fibronectin identified in the extracellular matrix surrounding the extravillous trophoblast at the uteroplacental junction contains an epitope called the "oncofetal domain," which is recognized by the monoclonal antibody FDC-6. When detected in cervicovaginal secretions of both symptomatic patients as well as asymptomatic women who have risk factors for early deliver, fetal fibronectin seems to be a marker for preterm delivery with a good positive predictive value (40-60 percent). A negative result has a negative predictive value of 99.5 percent for birth within 7 days and 92 percent for delivery before 37 weeks in those patients with signs and symptoms of preterm labor. In low-risk asymptomatic patients, the positive predictive value is lower (15-25 percent), but is important because women in this group, destined to deliver as a consequence of preterm labor, may have no other signs or symptoms to forebode preterm delivery. Fetal fibronectin testing could also be important in women in spurious preterm labor who may eventually deliver before 37 weeks' gestation. Although specific interventional studies are still needed, this test is an important step forward in the provider's armamentarium to reduce the impact of a preterm delivery.