Comparison of the Bishop score, ultrasonographically measured cervical length, and fetal fibronectin assay in predicting time until delivery and type of delivery at term

OBJECTIVE: Our aim was to compare the Bishop score, fetal fibronectin assays, and ultrasonographic measurement of cervical length to determine the best markers for time until spontaneous labor at term and risk of cesarean delivery, especially for the indication of lack of progress of dilatation. STUDY DESIGN: This prospective study included 128 singleton vertex pregnancies with no clinical evidence of membrane rupture or regular contractions and a prenatal consultation between 39 weeks 4 days' gestation and 40 weeks 3 days' gestation. We successively assayed for fetal fibronectin, determined the Bishop score, and measured cervical length by transvaginal ultrasonography. The end points were the percentage of patients with a spontaneous onset of labor in the week after these tests and the type of delivery. RESULTS: The spontaneous onset of labor within a 7-day period was closely associated with a Bishop score greater than or equal to 6 and with a cervical length less than or equal to 26 mm but not with a positive result of the fetal fibronectin assay. On the other hand, vaginal delivery was significantly associated with the fibronectin assay result but not with either the Bishop score or cervical length. CONCLUSIONS: The Bishop score and ultrasonographic measurement of cervical length are valuable for predicting the onset of spontaneous labor within 7 days (when these assessments are performed close to term), whereas the fetal fibronectin assay is useful for evaluating the risk of cesarean delivery. These tests thus provide different physiologic data that are useful for different purposes.