Fetal fibronectin: A new tool for the prediction of successful induction of labor

OBJECTIVE: The Bishop score is the only available tool for predicting successful labor induction. Vaginal fetal fibronectin has been shown to predict which patients will enter labor spontaneously, usually within 2 weeks. This study was designed to determine whether fetal fibronectin can also predict the success of labor induction. STUDY DESIGN: Term patients undergoing labor induction had a single swab from the vagina tested for fetal fibronectin before initiation of cervical ripening or oxytocin. The swab was tested with a blinded qualitative immunoassay for fetal fibronectin (positive ≥50 ng/ml). RESULTS: Of the overall 160 subjects, 108 had a positive and 52 had a negative fetal fibronectin result. Patients with a positive result had a lower cesarean section rate (15% vs 27%, p = 0.05) and shorter intervals to delivery, including first dose of prostaglandin to delivery interval (21.3 vs 35.8 hours, p = 0.0001) and first stage of labor (14.8 vs 21.2 hours, p = 0.0009). These differences remain similar even in nulliparous women with Bishop scores ≤5, with patients with positive results having statistically shorter intervals to delivery and similar differences in cesarean section rates (22% vs 35%), although this difference was not significant. In this subgroup more than half the patients in the negative results group (11/20) were undelivered after 24 hours and were judged to require a second dose of prostaglandin compared with only 2 of 53 in the group with positive results (p = 0.000001). By stepwise logistic regression analysis the predictive ability of a positive result for fetal fibronectin was found to be independent of the Bishop score. CONCLUSIONS: Vaginal fetal fibronectin appears to be an efficacious new test that independently predicts which patients will have shorter and easier inductions of labor and lower cesarean section rates, even nulliparous patients with low Bishop scores. This test has the potential for clinical utility and cost reduction. (Am J Obstet Gynecol 1996;175:1516-21.)