The Predictive Value of Trans-Vaginal Ultrasound Measurements Compared with Bishop Score in Determining Successful Induction of Labor

Determining the necessity of cesarean section (C/S) due to failure of induction of labor (IOL) is essential to avoid fetus distress. In this study, the performance of the Bishop score and trans-vaginal ultrasound measurements were compared to predict successful IOL, and the most useful cut-off points were estimated.

Nulliparous women with gestation age of > 37 weeks with a live fetus in cephalic presentation were invited to participate in this study. Bishop score was assessed by digital examination, and trans-vaginal ultrasound was used to measure cervical length. Trans-abdominal ultrasound was utilized to determine the fetal head position.

One hundred women entered the study. Multiple regression analysis revealed that the Bishop score and cervical length had a reliable predictive value in determining successful IOL. The cut-off points for predicting successful induction were 16 mm for cervical length and 5 for the Bishop score, using receiver operating characteristic curves (ROC). Both cervical length and Bishop score were good predictors for vaginal delivery (sensitivity and specificity of 85% and 67%, respectively for cervical length; and 84% and 70%, respectively for Bishop score).

Cervical length is a good predictor of successful IOL. Considering the painful process of digital exam, implementing trans-vaginal ultrasound is preferred.