Transvaginal ultrasonography is a useful means of assessing the cervix and predicting the duration of labor and obstetric outcomes. Studies comparing this method with the Bishop score, however, have yielded mixed results. The investigators compared these assessment methods in 80 women who were randomized to one or the other. The primary outcome was the proportion of women given prostaglandin before induction of labor. An unripe cervix calling for intracervical prostaglandin was defined as either a Bishop score less than 6 or a cervical length exceeding 30 mm with cervical wedging of less than 30% of total cervical length.
Women in the two diagnostic groups had similar cervical assessments initially. Nevertheless, prostaglandin was administered to 85% of women in the Bishop score group and to 50% of those having transvaginal ultrasonography (P = .001). Whereas 82.5% of women had a Bishop score less than 6, only 41% had an unripe cervix on ultrasound assessment. Correlation between the initial Bishop score and cervical length was significant. There were no substantial group differences in the interval to active labor, the interval to delivery, or the cesarean section rate. Obstetric outcomes also were similar except for a greater need to induce labor with oxytocin in the ultrasound group. There were no marked differences in perinatal outcomes. Two infants in the Bishop score group and four in the ultrasound group were admitted to the neonatal intensive care unit.
Using transvaginal ultrasonography rather than the Bishop score for assessing the cervix before inducing labor significantly lessened the need for intracervical prostaglandin treatment in this study. Successful induction and a good neonatal outcome were no less likely with ultrasound assessment.