Transvaginal ultrasonographic cervical measurement as a predictor of successful labor induction.

Abstract

Our purpose was to compare transvaginal cervical measurement and the Bishop score as indicators of duration of labor and successful induction of labor at term. This prospective observational study recruited women with singleton gestations scheduled for induction of labor at > or =37 weeks. Transvaginal ultrasonographic measurement of cervical length was performed and the Bishop score was determined, each by operators masked to the other measurement. Data were collected on parity, gestational age, mode of delivery, induction agent, induction-to-delivery interval, Bishop score, and cervical length measurement. A total of 77 women were analyzed. Vaginal delivery occurred in 69%. Both Bishop score and cervical length showed linear correlation with duration of labor (R(2) = 0.43, P <. 001; R(2) = 0.48, P <.001; respectively). Women with cervical length <3.0 cm had shorter labors (P <.001) and were more likely to be delivered vaginally (P <.001). Women with a Bishop score >4 also had shorter labors and were more likely to be delivered vaginally, with similar P values. A logistic regression model identified cervical length and parity as the only independent predictors of vaginal delivery. Both ultrasonographically measured cervical length and Bishop score predict duration of labor and likelihood of vaginal delivery. However, only cervical length and parity were independent predictors of mode of delivery.