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

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Objective: To determine the predictive value of cervicovaginal fetal fibronectin (fFN) concentrations ≥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 ≥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 ≥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 ≥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.