Oncofetal fibronectin in patients with false labor as a predictor of preterm delivery

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.

AACC Guidance Document on Laboratory Testing for the Assessment of Preterm Delivery

Identifying women with preterm labor who will go on to deliver prematurely is crucial to improving outcomes for mother and baby and for saving healthcare resources. Even among those with symptoms, the number of women who deliver preterm is low, and thus the low positive predictive value (PPV) and high negative predictive value (NPV) associated with available biomarkers does not substantially reduce the uncertainty of the clinical diagnosis. While there is some promise in the use of fetal fibronectin (fFN), interleukin 6 (IL-6), or placental alpha microglobulin 1 (PAMG-1) for predicting preterm birth (PTB), their use is unlikely to provide considerable clinical value in populations with a low prevalence. To provide real clinical benefit, a biomarker must demonstrate a high PPV to allow identification of the minority of symptomatic women who will deliver prematurely. As none of the currently available biomarkers exhibit this performance characteristic, we do not recommend their routine clinical use in populations with a pre-test probability of PTB of <5%. Limiting biomarker testing to only high-risk women identified on the basis of cervical length or other characteristics will increase the pre-testprobability in the tested population, thereby improving PPV. PAMG-1 is associated with a higher PPV than fFN and may show clinical utility in populations with a higher pre-test probability, but further work is required to conclusively demonstrate improved outcomes in this patient group.

The effect of transvaginal ultrasound, vaginal examination, or coitus on fetal fibronectin results: individual participant data from 6 cohort studies

OBJECTIVE

This study aimed to determine whether recent cervical manipulation via transvaginal ultrasound, sterile vaginal examination, or coitus affects the accuracy of fetal fibronectin results.

DATA SOURCES

An electronic search was performed in PubMed, Scopus, Embase, Ovid MEDLINE, ClinicalTrials.gov, Cochrane Library, and CINAHL using a combination of pertinent key words from inception to June 2019.

STUDY ELIGIBILITY CRITERIA

We included all observational studies that provided individual-level data on fetal fibronectin results after recent transvaginal ultrasound, sterile vaginal examination, or coitus.

STUDY APPRAISAL AND SYNTHESIS METHODS

Studies were appraised using the Newcastle-Ottawa Quality Assessment Scale for cohort studies. Individual participant data from the included studies were pooled for each intervention. The primary outcome was agreement between pre- and postmanipulation swabs, estimated using proportion agreement and kappa statistics with 95% confidence intervals. Secondary outcomes included frequency in which the fetal fibronectin result changed after cervical manipulation and percentage of discordant pairs. Baseline fetal fibronectin swabs were not obtained in studies examining coitus; therefore, the results of these articles were examined separately. Outcome data were combined to estimate the relative risk of a positive qualitative fetal fibronectin result after coitus and differences in the concentration of quantitative fetal fibronectin.

RESULTS

Of 807 studies identified, 6 were included. Three studies assessed the effect of transvaginal ultrasound (n=346 specimen pairs), 2 of sterile vaginal examination (n=122 specimen pairs), and 2 of coitus (n=262 specimen pairs) on fetal fibronectin results, with 1 study assessing the effect of more than 1 intervention. The proportion agreement between specimen pairs before and after transvaginal ultrasound and sterile vaginal examination was 93.4% (kappa, 0.69; 95% confidence interval, 0.57-0.81) and 88.5% (kappa, 0.69; 95% confidence interval, 0.54-0.84), respectively. For both transvaginal ultrasound and sterile vaginal examination, discordance with a positive preintervention fetal fibronectin and negative postintervention fetal fibronectin occurred more frequently than the converse. Patients reporting coitus within 24 to 48 hours were more likely to have a positive fetal fibronectin result than controls (39.7% vs 7.1%; relative risk, 5.6; 95% confidence interval, 3.0-10.6).

CONCLUSION

Cervical manipulation via transvaginal ultrasound or sterile vaginal examination does not significantly affect fetal fibronectin results; therefore, its use after these exposures is clinically acceptable. Conversely, the use of fetal fibronectin in the setting of recent coitus should continue to be discouraged.

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.

Evaluation of quantitative fFn test in predicting the risk of preterm birth

OBJECTIVE

To evaluate diagnostic accuracy of quantitative fetal fibronectin (qfFN) test in predicting preterm birth (PTB) risk <34 weeks' gestation or within 14 days from testing. We explored the predictive potential of the test in five-predefined PTB risk categories based on predefined qfFN thresholds (<10, 10-49, 50-199, 200-499 and ≥500 ng/mL).

METHODS

Measurement of cervicovaginal qfFN with Rapid fFN 10Q System (Hologic) in 126 women with singleton pregnancy (23-33 weeks' gestation) reporting signs and symptoms indicative of preterm labour (PTL).

RESULTS

For PTB prediction risk <34 weeks' gestation, sensitivity decreased from 100% to 41.7% and specificity increased from 0% to 99.1% with increasing fFN thresholds. Positive predictive value (PPV) increased from 9.5% to 83.3% with increasing qfFN thresholds, while negative predictive value (NPV) was higher than 90% among the fFN-predefined categories. Diagnostic accuracy results showed an area under a receiving operator characteristic (ROC) curve of 84.5% (95% CI, 0.770-0.903). For delivery prediction within 14 days from the testing, sensitivity decreased from 100% to 42.8% and specificity increased from 0% to 100% with increasing fFN thresholds. Diagnostic accuracy determined by the ROC curve was 66.1% (95% CI, 0.330-0.902).

CONCLUSIONS

The QfFN thresholds of tests are a useful tool to distinguish pregnant women for PTB prediction risk <34 weeks' gestation.

Fetal fibronectin as a biomarker of preterm labor: a review of the literature and advances in its clinical use

Spontaneous preterm birth (sPTB) is a challenge in obstetrics today, and is the leading cause of neonatal morbidity and mortality. The ability to predict preterm birth had, until recently, been poor. The biomarker fetal fibronectin (fFN), found at the maternal–fetal interface, when present in high concentrations in cervicovaginal fluid, has been shown to increase the risk of sPTB in symptomatic and asymptomatic women. Recently, further research has been performed into the applicability of such a test to clinical practice, and its effects on management decisions and patient outcomes. Owing to its high negative predictive value, a negative fFN result has been shown to reduce unnecessary interventions, change patient management and reduce healthcare costs, by allowing early reassurance and return to normal care pathways, while care can be concentrated on those at risk. The development of a bedside quantitative fFN test has shown promise to further improve the positive predictive abilities of fFN, as have combined predictive models with cervical length and fFN.

Fetal fibronectin as a predictor of spontaneous preterm birth: a European perspective

Preterm birth (PTB) is estimated to account for 6-10% of all births worldwide with 13 million PTBs occurring annually and 1 million resulting in death. The diagnosis of spontaneous preterm labor and accurate prediction of preterm delivery is notoriously difficult. Identification of effective risk assessment markers can potentially improve outcomes by enabling targeted therapy while allowing efficient use of resources and avoiding unnecessary interventions. Advances in perinatal medicine have not reduced PTB and effective measures that improve outcome are yet to be established. However, considerable progress has been made in the development of accurate methods (fetal fibronectin and cervical length assessment) to predict PTB in both symptomatic and asymptomatic high-risk women. The excellent negative predictive value of fFN has the ability to facilitate decision-making regarding admission, in utero transfer, administration of antenatal corticosteroids and/or tocolysis and has been shown to be cost-effective. This review describes the European perspective on the use of fFN and describes ongoing European clinical studies, which are appropriately designed with meaningful endpoints, which will undoubtedly facilitate a better understanding of test accuracy and cost-effectiveness within different populations.

Relationships between pregnancy outcomes, biochemical markers and pre-pregnancy body mass index

Objective:

We examined the relationships between pre-pregnancy maternal body mass index (BMI), pregnancy outcomes and biochemical markers.

Design:

This study was conducted as a cross-sectional analysis.

Subjects:

Korean women in their second and third trimesters of pregnancy were recruited at two hospitals in the metropolitan Seoul area. Pre-pregnancy BMI was categorized in four groups according to the Asia-Pacific standard.

Measurements:

Fasting blood samples were obtained and analyzed for serum levels of homocysteine, folate and high-sensitivity C-reactive protein (hs-CRP). Concentrations of fetal fibronectin were assessed in the cervix and vagina, and cervical length was measured.

Results:

Obese subjects had a lower education level and a lower income level than subjects of normal weight. The level of maternal stress was positively associated with pre-pregnancy BMI. Normal weight subjects were more likely to eat breakfast and consume meals of appropriate size than the rest of our sample. In overweight and obese subjects, weight gain during pregnancy was significantly lower than in the underweight and normal subjects. High pre-pregnancy maternal BMI increased the risks of preterm delivery (odds ratio (OR)=2.85, confidence interval (CI)=1.20–6.74), low-birth-weight (LBW) infants (overweight subjects: OR=5.07, CI=1.76–14.63; obese subjects: OR=4.49, CI=1.54–13.13) and macrosomia. In obese subjects, the average serum folate level was significantly lower than in the underweight subjects. In obese subjects, the average serum hs-CRP level was significantly higher than in the rest of our sample.

Conclusion:

Pregnancy outcomes are influenced by pre-pregnancy BMI. These findings suggest that women can minimize their risks of preterm delivery, LBW and macrosomia by maintaining normal pre-pregnancy BMI.

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.

IIICS de novo glycosylated fibronectin as a marker for invasiveness in urothelial carcinoma of the urinary bladder (UBC)

PURPOSE

The urothelial carcinoma is the most frequent malignancy of the urinary bladder (UBC). The transition into invasive growth is accompanied by several histological changes including an oncofoetal reorganization of the extracellular matrix. Recently, the occurrence of oncofoetal fibronectin with an O-linked glycosylation in the IIICS region (oncf Fn) was shown to be present in urine from UBC patients and was recommended as a tumour marker. Until now there are no data available regarding the source and distribution of oncf Fn in UBC and its value for the assessment of invasiveness.

METHODS

oncf Fn was analysed in noninvasive and invasive UBC using immunohistochemistry and western blot. Additionally, the mRNA expression of the IIICS splicing region was evaluated by quantitative real time RT-PCR.

RESULTS

Immunohistochemical results reveal a highly significant correlation of oncf Fn to invasiveness. Papillary tumours regularly show no positivity. In western blot, invasive UBC show a strongly increased amount of the 250 kDa oncf Fn. Additionally, several smaller bands could be shown suggesting a proteolytic processing of Fn. The mRNA of the IIICS region shows a 21.5-fold increase in invasive UBC compared with noninvasive carcinomas.

CONCLUSIONS

In summary, immunohistochemistry of oncf Fn is a valuable histological marker for invasiveness of urothelial carcinoma of the urinary bladder. The restricted and invasion-associated tissue distribution of immunoreactivity enables to monitor the recurrence of invasive UBC by a quantitative evaluation of IIICS O-linked glycosylated Fn in urine.

Biochemical markers for the prediction of preterm delivery

Preterm delivery is the largest contributor to perinatal morbidity and mortality throughout the world. In the United States, nearly 1 in every 8 infants is born prematurely. Although a portion of these births are indicated preterm deliveries, the frequency of spontaneous preterm birth has remained largely constant over the past 50 years.

Biochemical markers for the prediction of preterm labor

Premature labor and subsequent premature delivery is the major cause of perinatal death in the world. Numerous risk factors identify patients at jeopardy for preterm labor, but with poor sensitivity. Several biologic and biochemical markers have been recently studied that may allow early identification of patients at risk of preterm delivery. Although two markers have received Food and Drug Administration approval, a number of other tests also may ultimately prove useful.

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.

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.

Testing for risk of preterm delivery

Four discrete mechanisms for the pathogenesis of PTD have been described but they share a final common pathway. Moreover, although the mechanisms have distinct clinical characteristics, they are not mutually exclusive. As an example, triplet gestations are more likely to be associated with periconceptional intrauterine manipulations predisposing to infection, as well as fetal growth restriction, decidual hemorrhage, and pathologic uterine distention. An improved understanding of these pathologic pathways has led to the development of new tests to predict PTD. Use of multiple markers (eg, serum CRH, salivary E3, cervical IL-6, TAT, and fFN) holds promise for implementing targeted interventions to prevent PTD.

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.

Failure of cervical fibronectin to predict premature delivery in a population of monofetal pregnancies with idiopathic preterm labor

OBJECTIVE

The purpose of the study was to evaluate the correlation between the presence of cervical fibronectin in a high-risk population of women with symptoms of preterm labor and the occurrence of preterm delivery or the need for aggressive tocolysis.

STUDY DESIGN

One hundred and thirty women presenting with symptoms of threatened preterm labor were included. Cervical sampling for detection of fibronectin was performed on admission and every day until discharge or delivery. Time to delivery, length of hospital stay, use of indomethacin, delivery before 37 weeks of GA, mean term of delivery and failure of tocolysis to prevent delivery were compared to fibronectin test results. Data were analyzed using Student's t-test for continuous variables and the chi(2) test or Fisher exact test for discrete variables.

RESULTS

No correlation could be found between the results of fibronectin cervical sampling on admission and any of the outcome parameters studied. Test performances were low (sensitivity 28%, specificity 57%, positive predictive value 19%, negative predictive value 69%). Results were not modified when the findings of repeated tests were taken into account.

CONCLUSION

Cervical fibronectin failed to discriminate a subgroup of symptomatic women delivering prematurely. The prognostic value of fibronectin testing was not better than clinical data in our series. This observation is in disagreement with previous studies on the diagnostic value of vaginal or cervical fibronectin in preterm labor.

Pregnancy outcome in women with preterm labor symptoms without cervical change

OBJECTIVE

This study was undertaken to determine pregnancy outcome in women who have preterm labor symptoms without cervical change according to fetal fibronectin status.

STUDY DESIGN

Patients who were examined at the obstetric emergency department with symptoms of preterm labor but without cervical change underwent fetal fibronectin collection. Pregnancy outcome and fetal fibronectin results were analyzed after delivery.

RESULTS

Of the 235 patients sampled, 20% (n = 48) had positive fetal fibronectin results. The mean +/- SD gestational age at delivery was lower in women with positive fetal fibronectin results (34.2 +/- 4.1 vs 37.7 +/- 2.3 weeks; P <.001); these women were more likely to deliver preterm as a result of preterm labor than women with other obstetric indications (46% vs 19%; P <.001). Infants born to these women demonstrated lower birth weight (2317 +/- 895 g vs 2877 +/- 557 g; P =.003), were more likely to be admitted to the neonatal intensive care unit (42% vs 14%; P <.001), and were more likely to die in the neonatal period (11% vs 0%; P <.001).

CONCLUSION

Patients with symptoms of preterm labor but without cervical change who have negative fetal fibronectin results are less likely to deliver preterm. Therefore in women with symptoms but without cervical change fetal fibronectin should be considered for risk assessment.

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.

Fetal fibronectin detection as a predictor of preterm birth in actual clinical practice

OBJECTIVE

This study was undertaken to determine whether fetal fibronectin determination is more useful for predicting preterm delivery in clinical practice than it has appeared to be in prospective blinded studies.

STUDY DESIGN

Charts of 151 patients with fetal fibronectin tests performed during 2 years were reviewed. Patients were included if they had symptoms of preterm labor, a singleton pregnancy at 24 to 35 weeks' gestation, intact membranes, and cervical dilatation < or =3 cm.

RESULTS

Complete data were available for 85 tests. For delivery within 7 days after specimen collection the sensitivity, specificity, positive predictive value, and negative predictive value were 89%, 84%, 40%, and 98%, respectively. The positive predictive value was greater (P <.002) than those reported in three prospective studies evaluating delivery within 7 days in patients with symptoms. Gestational age at delivery and birth weight were lower for patients with positive results (P <. 0001 and P <.006, respectively). Patients with positive results were also treated more with tocolysis, corticosteroid use, and hospitalization than were patients with negative results. For direct comparison with studies of patients with cervical dilatation <3 cm, only 4 patients with cervical dilatation of 3 cm were enrolled. All 4 had negative results of fetal fibronectin testing, and their outcomes therefore did not affect the positive predictive value.

CONCLUSION

The positive predictive value of fetal fibronectin measured in actual clinical practice was significantly greater for delivery within 7 days than has been reported in blinded prospective studies.

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.

Fetal fibronectin as a marker for an imminent (preterm) delivery. A new technique using the glycoprotein lectin immunosorbent assay

We have developed a new 'glycoprotein lectin immunosorbent assay' (GLIA) which permits the obstetrician to identify accurately pregnant women at risk for preterm delivery. This GLIA uses two lectins for the quantitative detection of glycosylation variants of fibronectins, namely, Maackia amurensis lectin (MAA) for the detection of fetal fibronectin (fFN), and Sambucus nigra lectin (Elderberry bark lectin; SNA). Fibronectin was quantitated in cervicovaginal secretions, amniotic fluid, and plasma of pregnant women. Detection of fFN in cervicovaginal secretions was considered to indicate a high risk of imminent delivery. The results were as follows: (1) The GLIA could differentiate between pregnant women after the onset of labour and/or with rupture of membranes and women without any signs of an imminent delivery (sensitivity 94%, specificity 96%, p < 0.001). (2) Differentiation was possible between asymptomatic pregnant women delivering within 10 days of sampling or after more than 10 days (sensitivity 93%, specificity 99%; p < 0.001). (3) If fFN was present in the cervicovaginal secretions, delivery occurred within 10 days of sampling irrespective of preterm delivery or delivery at term (p < 0.001). Thus, this GLIA is a useful assay for identifying those asymptomatic pregnant women who will deliver within 10 days of sampling.

Biochemical markers for preterm labor and birth: what is their role in the care of pregnant women?

Two biochemical tests, one for oncofetal fibronectin (fFN) and the other for estriol found in maternal saliva (SalEst) have been developed to improve the ability to predict preterm labor and birth. Fetal fibronectin is a protein secreted by the trophoblast and not normally present in vaginal and cervical secretions late in pregnancy. The presence of fFN between 22 and 37 weeks gestation may be a marker for preterm labor. Salivary estriol is a form of estrogen produced in the placenta from fetal precursors. Normally, estriol rises during pregnancy--the rise being accelerated 3 to 5 weeks prior to both term and preterm births. Both tests have high negative predictive values. This may serve to prevent unnecessary treatment of women with uterine contractions who are not truly in preterm labor. The fFN specimen is collected during vaginal examination. Sexual intercourse or vaginal examination within the prior 24 hours, vaginal bleeding, and uterine contractions may lead to a false positive test. Salivary estriol may be collected by the woman in her own home; however, specific instructions about eating, drinking, smoking, and the timing of saliva collection must be followed. Further study of both tests is required to determine their potential for reducing rates of preterm birth.

Fetal fibronectin detection in preterm labor: evaluation of a prototype bedside dipstick technique and cervical assessment

OBJECTIVE

The aims of this study were to evaluate a prototype bedside test for fetal fibronectin detection in women with symptoms of preterm labor, to compare the efficacy of obtaining fetal fibronectin swabs with and without a speculum, and to assess the value of combining the fetal fibronectin test with cervical dilatation for predicting delivery within 10 days.

STUDY DESIGN

This investigation prospectively studied a cohort of women with symptoms of preterm labor (n = 121), gestational age between 24 and 33 6/7 weeks, and cervical dilatation </=3 cm. Vaginal swabs for fibronectin testing with the bedside dipstick Fetal Fibronectin Membrane Immunoassay test (Adeza Biomedical, Sunnyvale, Calif) were obtained with and without a speculum. Results were not available to the clinicians.

RESULTS

Twenty-two percent of the fetal fibronectin samples collected with a speculum (27/121) yielded positive results. The incidence of delivery within 10 days of testing was 14% (17/121). Fetal fibronectin detection predicted delivery within 10 days with sensitivity, specificity, and positive and negative predictive values of 65%, 85%, 41%, and 94%, respectively. The positive and negative likelihood ratios were 4.3 and 0.41, respectively. There was substantial association between samples obtained with and without a speculum (Cohen kappa statistic 0.65, 95% confidence interval 0.44-0.87). Cervical dilatation >/=1 cm predicted delivery within 10 days with sensitivity, specificity, and positive and negative predictive values of 71%, 87%, 46%, and 95%, respectively, with positive and negative likelihood ratios of 5.5 and 0.33, respectively. Combination of fetal fibronectin testing with cervical dilatation >/=1 cm did not significantly improve the fetal fibronectin test characteristics. After exclusion of women with slight vaginal bleeding, cervical dilatation >/=1 cm and fetal fibronectin status remained the only independent variables associated with delivery within 10 days.

CONCLUSION

Fetal fibronectin testing according to this prototype may have a limited role in clinical decision analysis. In this study a cervical dilatation >/=1 cm had predictive values equivalent to those of the fetal fibronectin test, and it should be evaluated further in a clinical setting.

Cervicovaginal fetal fibronectin testing in threatened preterm labour--translating research findings into clinical practice

A retrospective audit was undertaken involving 70 women with a singleton pregnancy who attended hospital with symptoms of threatened preterm labour prior to 34 weeks' gestation and who had a bedside fetal fibronectin (FFN) Membrane Immunoassay Kit Test (Adeza Biomedical) performed. The aim of the study was to determine if the results of the FFN test when used in routine clinical practice would be similar to those of a previous research study (1) that was performed at the same centre, and whether or not knowledge of the result of the FFN test might influence clinical management. The audit revealed that the sensitivity of the FFN test in the prediction of delivery prior to 34 weeks' gestation was 90%, the specificity was 82%, whilst the positive and negative predictive values were 45% and 98% respectively. These results were very similar to those of the previous, blinded research study. Compared to women with a negative FFN test, more women with a positive FFN test received corticosteroids (100% versus 71%, p=0.02) and tocolysis (35% versus 12%, p=0.04) and more remained in hospital longer than 24 hours (85% versus 56%, p=0.1).

Cervicovaginal fetal fibronectin concentrations: predictive value of impending birth in postterm pregnancies

OBJECTIVE

To determine the predictive value of cervicovaginal fetal fibronectin (fFN) concentrations > or =50 ng/ml for spontaneous onset of labour within 3 days in pregnancies of 41 weeks gestation or more.

STUDY DESIGN

In the Department of Obstetrics, Leiden University Medical Centre, and of the Diaconessen Hospital, Voorburg (The Netherlands), 126 cervicovaginal secretions of fFN, from 80 consenting women between 287 and 304 days gestation were collected. Pregnant women underwent sterile speculum examinations for cervicovaginal sampling from the 41st week onwards. The fFN concentration in these samples was determined with a quantitative solid-phase enzyme-linked immunosorbent assay. Concentrations of <50 ng fFN per ml were characterised as negative test results, meaning that spontaneous delivery would not take place within 3 days, and those of > or =50 fFN ng/ml were taken as positive test results. Sensitivity and specificity of the fFN test were calculated for predicting spontaneous birth. Parametric and nonparametric tests were used for evaluating differences and correlations.

RESULTS

Spontaneous delivery took place after 2.5+/-2.5(SD) days with fFN values > or =50 ng/ml and after 4.7+/-3.6 days with fFN concentrations <50 ng/ml (P<0.001). Sensitivity and specificity of the fFN test predicting spontaneous onset of labour within 3 days, were 0.71 [95% confidence interval (CI) 0.58-0.86] and 0.64 (95% CI 0.48-0.78). If fFN > or =50 ng/ml then a spontaneous onset of labour is more likely to occur within 3 days (odds ratio 4.5 (95% CI 1.8-11.3).

CONCLUSIONS

The fFN test does not predict accurately enough whether or not birth will take place within 3 days of sampling. Nevertheless, the higher odds for spontaneous delivery within a few days when the test is positive may be of use in planning adjusted induction of labour.

Study of cervicovaginal fetal fibronectin status to guide treatment of threatened preterm labour

A sequential controlled pilot study of 48 women (16 study, 32 controls) was performed to explore the place of bedside fetal fibronectin testing in the management of apparent preterm labour; 80% of the study group were successfully managed without tocolytic therapy, on the basis of fetal fibronectin test results, without detriment to the babies. Rapid bedside fetal fibronectin testing holds promise that protocols for management of women in apparent preterm labour, with intact membranes and without significant cervical dilatation, may be altered so that most of the unnecessary use of tocolytic drugs is avoided.

Has the use of home monitors, fetal fibronectin, and measurement of cervical length helped predict labor and/or prevent preterm delivery in twins?

Home monitoring accurately detects contractions, and thus is useful in predicting preterm labor. Appropriate physician action is necessary to significantly prolong pregnancy even in the presence of evidence of excessive contractions. Despite conflicting studies, the majority of evidence heavily favors the use of monitoring as part of a comprehensive preterm birth prevention program. Indeed, monitoring has greater clinical utility in twin gestations because of the recognized propensity for preterm labor. Fetal fibronectin is one of the most sensitive and specific markers for preterm labor and subsequent early delivery presently available. It appears to be equally effective in multifetal gestations compared with singleton gestations, but intervention trials are needed to substantiate its clinical effectiveness. Cervical status monitoring by ultrasound correlates inversely with preterm labor, but studies in twin gestation are currently lacking. Other markers, such as salivary estriol for preterm labor, have yet to be assessed as predictors of preterm labor among multifetal gestations.

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.

The fast-reacting fetal fibronectin test: a screening method for better prediction of the time of delivery

OBJECTIVE

Our aim was to determine from what time onward fetal fibronectin is consistently detectable in the cervicovaginal secretions before delivery and to what extent the actual time of delivery can be better determined by this procedure than by the sole use of the Bishop score.

STUDY DESIGN

A fast-reacting fetal fibronectin test was performed on 206 women on their expected date of confinement. In addition, the cervical status was evaluated with use of a modified Bishop score. Follow-up evaluations were subsequently carried out in the course of the routine examinations.

RESULTS

Women with a positive fetal fibronectin test result and a high Bishop score were delivered after a median of 1.7 days. Conversely, women with a negative fetal fibronectin test result and a low Bishop score were delivered after a median of 7.1 days.

CONCLUSION

Determination of fetal fibronectin in combination with the Bishop score makes it possible to predict the actual time of delivery with a greater degree of accuracy.

Fetal fibronectin as a predictor of preterm birth in patients with symptoms: a multicenter trial

OBJECTIVE

Our aim was to determine whether the presence of fetal fibronectin in vaginal secretions of patients with symptoms suggestive of preterm labor predicts preterm delivery.

STUDY DESIGN

Patients who were examined at the hospital between 24 weeks' and 34 weeks 6 days' gestation with intact membranes, no prior tocolysis, symptoms suggestive of preterm labor, and cervical dilation < 3 cm were recruited at 10 sites. Swabs of the posterior fornix were assayed for the presence of fetal fibronectin by monoclonal antibody assay, with a positive result defined as > or = 50 ng/ml. Results were not available to the managing physicians. Tocolysis was used when clinically indicated after specimen collection.

RESULTS

A total of 763 patients had fetal fibronectin results and pregnancy outcome data available for analysis. Fetal fibronectin was detected in specimens from 150 (20%) patients. Compared with patients who had negative results, patients who had positive results for fetal fibronectin were more likely to be delivered within 7 days (relative risk 25.9 [95% confidence interval 7.8 to 86]), within 14 days (relative risk 20.4 [95% confidence interval 8.0 to 53]), and before 37 completed weeks (relative risk 2.9 [95% confidence interval 2.2 to 3.7]). The negative predictive values for delivery within 7 days, within 14 days, and at < 37 weeks were 99.5%, 99.2%, and 84.5%, respectively. When we used multiple logistic regression analysis to control for potential confounding variables among singleton pregnancies, only the presence of fetal fibronectin (odds ratio 48.8, 95% confidence interval 7.4 to 320), prior preterm birth (odds ratio 8.3, 95% confidence interval 1.5 to 46.6), and tocolysis (odds ratio 4.1, 95% confidence interval 1.0 to 16.0) were associated with birth within 7 days; fetal fibronectin (odds ratio 3.6, 95% confidence interval 2.2 to 5.9), prior preterm birth (odds ratio 2.5, 95% confidence interval 1.4 to 4.4), cervical dilatation > 1 cm (odds ratio 2.9, 95% confidence interval 1.6 to 5.2), and tocolysis (odds ratio 4.5, 95% confidence interval 2.8 to 7.2) were all independently associated with delivery before 37 weeks.

CONCLUSION

In a population of patients with symptoms, the presence of fetal fibronectin in vaginal secretions best defines a subgroup at increased risk for delivery within 7 days; the high negative predictive value of fetal fibronectin sampling supports less intervention for patients with this result.

A single cervical fetal fibronectin screening test in a population at low risk for preterm delivery: an improvement on clinical indicators?

OBJECTIVE

To assess the accuracy of a single cervical fetal fibronectin test to predict spontaneous preterm delivery in an unselected antenatal population.

DESIGN

A prospective blind cohort study.

SETTING

Antenatal clinic of a teaching hospital in a Brussels semiurban area.

PARTICIPANTS

An unselected group of 170 women followed at the antenatal clinic.

METHODS

A single cervical sample was obtained between 24 and 33 completed weeks of pregnancy. The fibronectin test was compared with clinical evaluation and their predictive properties were assessed.

RESULTS

Fifteen women were excluded from the analysis because of elective preterm delivery for medical indications or loss to follow up. Of the 155 remaining women, nine (7%) had a spontaneous preterm delivery. For a single fetal fibronectin test, the sensitivity was 26.7%, the specificity 95.7%, and the positive and negative predictive values 40.0% and 92.4%, respectively. The likelihood ratio of a positive was similar to that of clinical predictors of preterm birth (LR = 6.2; 95% CI 2.0-19.6). Sensitivities were low for both clinical criteria and the fetal fibronectin test.

CONCLUSIONS

Because of low sensitivity in a low risk population, screening for preterm delivery should not be based on the result of a single fetal fibronectin test alone. However, due to its high specificity the test might be useful in avoiding unnecessary medical intervention.

Rapid fetal fibronectin swab-test in preterm labor patients treated by betamimetics

OBJECTIVE

A preliminary study to examine the value of a rapid fetal fibronectin swab-test used as a bedside test in the prognosis of preterm labor.

STUDY DESIGN

Women presenting with preterm labor and intact membranes and less than 3 cm dilated were enrolled in a single referral center. Cervicovaginal swabs were assessed for the presence or absence of fetal fibronectin by means of a rapid monoclonal antibody assay the positivity of which was revealed by a colorimetric reaction. Results were compared with uterine contractions frequency, Bishop cervical score, duration of tocolysis and interval to delivery. The predictive value of fetal fibronectin test for delivery within 7, 14 or 21 days from sampling and before 32 and 37 weeks' of gestation was assessed in the two groups.

RESULTS

Among 124 eligible patients, 19 presented with a positive fibronectin test and 105 with a negative one. Gestational age at sampling, Bishop cervical score and duration of tocolysis were identical in the two groups. The number of contractions was significantly lower and gestational age at delivery was significantly higher in the fibronectin negative group. Fetal fibronectin in cervicovaginal secretions has a high sensitivity (89%) for delivery within 7 days. Absence of fetal fibronectin in cervicovaginal secretions of patients presenting with uterine contractions could rule out preterm labor within 7 and 14 days with a predictive value of 99 and 95.2%, respectively. In negative fetal fibronectin patients, preterm delivery before 32 and 37 weeks' is unlikely to occur with a predictive value of 97 and 85%, respectively.

CONCLUSION

Cervicovaginal fetal fibronectin detected by a rapid bedside swab-test in women with symptoms of preterm labor compares favourably with quantitative assays and could prove useful in the management of preterm labor. This should be confirmed in a longer prospective study.

The diagnostic accuracy of cervico-vaginal fetal fibronectin in predicting preterm delivery: an overview

OBJECTIVE

To determine the accuracy with which cervico-vaginal fetal fibronectin predicts preterm delivery using systematic quantitative overview of the available literature.

DESIGN

Online searching of MEDLINE database (1966 to April 1996), scanning of bibliography of known primary and review articles and review of recent journal issues. Study selection, assessment of study quality and data extraction were performed in duplicate under masked conditions. Likelihood ratios were generated in subgroups of symptomatic and asymptomatic pregnant women by pooling data from different studies. An LR of > 10 or < 0.1 indicated conclusive changes in the pretest probability of preterm delivery while an LR of 5-10 or 0.2-0.1 indicated only moderate changes.

PARTICIPANTS

Seven hundred and twenty-three symptomatic women with threatened preterm labour included in nine studies and 847 asymptomatic women (635 low risk and 212 high risk) included in six studies selected for meta-analyses.

MAIN OUTCOME MEASURES

Likelihood ratios for positive and negative test results using delivery at < 37 and < 34 weeks of gestation, and within one week of testing as outcome measures.

RESULTS

In symptomatic women a positive test predicted delivery < 37 weeks of gestation with a pooled likelihood ratio (LR) of 4.6 (95% CI 3.5-6.1) while a negative test had a pooled LR of 0.5 (95% CI 0.4-0.6). For delivery < 34 weeks of gestation, the pooled LR was 2.6 (95% CI 1.8-3.7) for a positive test and 0.2 (95% CI 0.1-0.5) for a negative test. For delivery within one week of testing, the pooled LR was 5.0 (95% CI 3.8-6.4) for a positive test and 0.2 (95% CI 0.1-0.4) for a negative test. In asymptomatic women at low risk of delivery < 37 weeks of gestation the pooled LR was 3.2 (95% CI 2.2-4.8) for a positive test and 0.8 (95% CI 0.7-0.9) for a negative test. In high risk asymptomatic women using delivery < 37 weeks of gestation as an outcome measure the pooled LR was 2.0 (95% CI 1.5-2.6) for a positive test and 0.4 (95% CI 0.2-0.8) for a negative test. For delivery < 34 weeks of gestation in high risk, asymptomatic women the pooled LR was 2.4 (95% CI 1.8-3.2) for a positive test and 0.6 (95% CI 0.4-0.9) for a negative test.

CONCLUSION

The presence of fetal fibronectin in cervico-vaginal mucus has limited accuracy in predicting preterm delivery as the likelihood ratios for positive and negative test results generated only minimal to moderate changes in the pretest probability of preterm birth.

Maternal plasma fibronectin: a predictor of preterm delivery

OBJECTIVE

Current opinion holds that there are several distinct groups among patients with preterm labour: one of them is characterized by bacterial infection, another one by the presence of placental vascular abnormalities with endothelial damage. The aim of this study was to investigate plasma fibronectin, a suspected biochemical marker of endothelial damage, as an indicator for pregnancies with a high risk of preterm delivery.

METHODS

Plasma fibronectin levels were measured in patients with preterm labour (n = 80) and in healthy pregnant women with uncomplicated (control) pregnancies (n = 64) between the 22nd and 36th week of gestation. Furthermore, the plasma concentrations of fibronectin in 15 newborns at term and ten babies born preterm were measured to study the relationship between preterm delivery and plasma fibronectin concentration in newborns. Fibronectin was measured by nephelometry.

RESULTS

The mean concentration of fibronectin in patients with preterm labour was 0.44 g/l (S.D., 0.15) vs. 0.25 g/l (S.D., 0.12) in uncomplicated control pregnancies matched for gestational age. In control patients who actually delivered at term, fibronectin values were found to be lower than in control patients who underwent preterm delivery (0.25 g/l; S.D., 0.05; vs. 0.46 g/l; S.D., 0.15; P < 0.05). Particularly high values were detected in patients with preterm labour delivering before 32 weeks of gestation (0.60 g/l; S.D., 0.16). There was no significant difference between fibronectin concentrations in the umbilical arterial and venous blood of premature infants and mature infants. Leucocyte concentration, bacteriological smear and cervical dilatation did not correlate with fibronectin concentrations in patients with preterm delivery or controls.

CONCLUSION

We conclude that the higher plasma concentrations of fibronectin in women with preterm labour may be a biochemical marker and a predictor of preterm delivery.

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.

Predictors of positivity for fetal fibronectin in patients with symptoms of preterm labor

OBJECTIVE

Identifying patients at risk for preterm delivery continues to be difficult. We analyzed fetal fibronectin immunoassays in 763 subjects with threatened preterm delivery from 10 clinical sites.

STUDY DESIGN

Symptomatic women between 24 weeks 0 days and 34 weeks 6 days with intact amniotic membranes and cervical dilatation <3 cm were included. Specimens were obtained from the posterior vaginal fornix and concentrations of fetal fibronectin were measured by enzyme-linked immunosorbent assay. A total of 150 (20%) patients had positive results for the fetal fibronectin immunoassay. The simultaneous effects of multiple variables on predicting positive fetal fibronectin immunoassay results were analyzed with use of logistic regression models. Variables included were patient age (mean 24.2 years), race (40% white), gravidity (29% primigravid), history of previous premature infants (15%), sexual activity within 24 hours of sample collection (66/763 or 9%), cervical examination within 24 hours of sample collection (107/763 or 14%), vaginal bleeding (118/759 or 16%), uterine contractions (192/750 or 26% with three or more in 1 hour), cervical dilatation (94/763 or 12% with dilatation between 1 and 3 cm), estimated gestational age at sampling (mean 30 weeks 2 days).

RESULTS

Regardless of the variable selection process (e.g., forward, backward, or stepwise), the reduced model showed five significant variables in predicting positive fetal fibronectin: cervical dilatation (chi2 33.5, p = 0.0006), sexual activity within 24 hours of sample collection (chi2 22.9, p < 0.0001), presence of vaginal bleeding (chi2 17.0, p < 0.0001), cervical examination within 24 hours of sample collection (chi2 11.6, p < 0.0006), and uterine contractions (chi2 6.8, p = 0.01). Deletion of the true positive subset did not change these variables or the magnitude of risk.

CONCLUSION

Cervical dilation or manipulation predicts positive fetal fibronectin assays and may serve to explain some of the false-positive results generated by the test.

Evaluating the risk of preterm delivery: a comparison of fetal fibronectin and transvaginal ultrasonographic measurement of cervical length

OBJECTIVE

Our purpose was to compare the predictive values for preterm delivery of fetal fibronectin and cervical length measured by transvaginal ultrasonography and to determine whether performing both tests improves their separate predictive values.

STUDY DESIGN

This prospective blinded study performed both tests on 76 patients hospitalized with signs of premature labor between 24 and 34 weeks of gestation. The outcome measure was delivery before 37 weeks' gestation.

RESULTS

The rate of preterm bith was 26.3% (20/76). The predictive values of fetal fibronectin and of a cervical length of < or = 26 mm, considered separately, were approximately equal, and the negative predictive value of each was excellent (86.6% and 89.1%, respectively). This value improved slightly when positive fetal fibronectin, a cervical length < or = 26 mm, or both defined abnormality (negative predictive value 94.4%). The positive predictive values, although less helpful, were still useful (45.2% and 50.0%, respectively). Combining both indicators did not noticeably improve the positive predictive value (52.4%). The risk of preterm delivery for a patient with a positive fetal fibronectin level and a short cervix was high (odds ratio 13.9, 95% confidence interval 3.7 to 52.2).

CONCLUSION

Fetal fibronectin and cervical length are approximately equivalent in their ability to distinguish between patients at high and low risk for preterm delivery. For physicians equipped to perform transvaginal ultrasonography, however, the additional information about the fibronectin level provides only slight benefits.

Oncofetal fibronectin: new insight into the physiology of implantation and labor

Oncofetal fibronectin is a newly studied protein produced by the trophoblast and is present in plasma and cervicovaginal secretions of pregnant women as labor approaches or when they have certain complications of pregnancy. Alterations in levels of oncofetal fibronectin occur in preterm labor, postterm pregnancy, and pregnancy-induced hypertension. Determining the presence or absence of full-term and preterm labor often is difficult in the clinical setting, and decision-making sometimes is hindered by the lack of a specific biochemical marker for labor. Oncofetal fibronectin may become a clinical indicator or predictor of true labor, preterm labor, or some complications of pregnancy. Assay techniques that identify clinically meaningful levels of oncofetal fibronectin are being developed and investigated and soon may be available to screen and identify pregnant women at risk. Research findings suggest new paths for investigation that may lead to important interventions in health care directed at identifying and decreasing maternal and neonatal morbidity and mortality. This article reviews pertinent aspects of placentation and the rationale for using oncofetal fibronectin detection as a clinical marker for abnormal pregnancy states.

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

OBJECTIVE

We examined clinical value of cervical fetal fibronectin detection by a quantitative enzyme-linked immunosorbent assay as a predictor of preterm delivery in a population (n = 111) of middle-class pregnant women considered to be at low risk for preterm delivery.

STUDY DESIGN

In this prospective study, fetal fibronectin samples from cervicovaginal secretions were obtained biweekly from 24 to 34 weeks' gestation.

RESULTS

Twenty-two (20%) patients had at least one positive fetal fibronectin test result. Eleven women (10%) were delivered spontaneously at < 37 weeks; seven of these had at least one positive fetal fibronectin test result (positive predictive value = 31.8%, sensitivity = 63.6). An additional three women were delivered prematurely because of other obstetric indications, and all had negative fetal fibronectin test results. The remaining 15 patients with at least one positive fetal fibronectin test result were delivered at term (> or = 37 weeks). Of the seven women with positive fetal fibronectin results who were delivered prematurely, five were delivered within 2 weeks of obtaining a positive result. However, there were no obvious clinical discriminators between true-positive and false-positive fetal fibronectin results. Eighty-nine women tested negative, and 85 of these women were delivered at term (specificity = 82.0%). The negative predictive value of fetal fibronectin as a predictor of term delivery in this low-risk population is 96.6%, with odds ratio = 8.8 (95% confidence interval 1.9 to 40.3), relative risk = 6.9 (95% confidence interval 1.8 to 26.6), and Fisher Exact Test p = 0.007.

CONCLUSIONS

Although negative biweekly fetal fibronectin determinations for prediction of preterm delivery in this low-risk obstetric population correlate well with the absence of preterm delivery, they are of limited clinical value for the prediction of preterm birth.

Fibronectin binding and cell surface hydrophobicity contribute to adherence properties of group B streptococci

The matrix protein, fibronectin, which is detectable in various tissues, when present in the vaginal fluid of women in labour, indicates the rupture of membranes. It is known that many bacteria adhere to fibronectin, thus establishing a first step of infection. In women in labour, group B streptococci are common agents of chorioamnionitis. For group B streptococci, unspecific adherence mechanisms like negative net charge and hydrophobic interactions have already been discussed in literature. In the present study, group B streptococci isolates from 57 patients with premature rupture of membranes were studied for fibronectin binding activities, using a particle agglutination assay and for cell surface hydrophobicity, by testing adhesion to hydrocarbons. Particle agglutination assays and adhesion assays were done with strains grown on blood-containing media and media without blood. Fibronectin binding was shown to be present in 14 and 11 out of 57 isolates grown on Mueller-Hinton and Tryptic Soy agar, respectively. When the strains were grown on blood-containing media, fibronectin-binding was found to be concomitant with decreased hydrophobicity. According to the results obtained in a total of 57 strains, cell surface hydrophobicity is an unspecific adhesion factor in group B streptococci. Fibronectin binding seems to be an additional adherence factor in some of the strains and may be assumed to play a major role in establishing infectious processes.