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

OBJECTIVE: Our aim was to compare the Bishop score, fetal fibronectin assay s, and ultrasonographic measurement of cervical length to determine the bes t markers for time until spontaneous labor at term and risk of cesarean del ivery, especially for the indication of lack of progress of dilatation. STUDY DESIGN: This prospective study included 128 singleton vertex pregnanc ies with no clinical evidence of membrane rupture or regular contractions a nd a prenatal consultation between 39 weeks 4 days' gestation and 40 weeks 3 days' gestation. We successively assayed for fetal fibronectin, determine d the Bishop score, and measured cervical length by transvaginal ultrasonog raphy. The end points were the percentage of patients with a spontaneous on set 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 a ssociated with a Bishop score greater than or equal to 6 and with a cervica l 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 significan tly associated with the fibronectin assay result but not with either the Bi shop 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 feta l fibronectin assay is useful for evaluating the risk of cesarean delivery. These tests thus provide different physiologic data that are useful for di fferent purposes.