Preinduction sonographic measurement of cervical length in the prediction of successful induction of labor

TLDR

Induction of labor occurs in about 20 % of pregnancies, yet roughly 20 % of those inductions result in cesarean delivery, and the commonly used Bishop score is subjective and has limited predictive accuracy. This study aims to compare preinduction sonographic cervical length with the Bishop score in predicting successful vaginal delivery within 24 hours of induction. In a multicenter cohort of 240 singleton pregnancies at 37–42 weeks, cervical length was measured by transvaginal sonography while the Bishop score was obtained by digital examination. Cervical length, Bishop score, and parity independently predicted vaginal delivery within 24 hours, with cervical length alone providing the strongest prediction (cut‑off 28 mm, sensitivity 0.87, specificity 0.71), outperforming the Bishop score (cut‑off 3, sensitivity 0.58, specificity 0.77) as shown by ROC and Kaplan–Meier analyses.

Abstract

Abstract Background Induction of labor is carried out in approximately 20% of pregnancies. However, approximately 20% of women having induction of labor end up having a Cesarean delivery. The traditional method of predicting whether an induced labor will result in successful vaginal delivery is based on the preinduction ‘favorability’ of the cervix as assessed by the Bishop score. However, this assessment is subjective and several studies have shown a poor predictive value for the outcome of induction. Objectives To examine the relationship between preinduction sonographically measured cervical length and the Bishop score and to compare the two measurements in the prediction of successful vaginal delivery within 24 h of induction. Methods In this multicenter study, preinduction cervical assessment was undertaken in 240 women with singleton pregnancies at 37–42 weeks of gestation. The Bishop score was assessed by digital examination and the cervical length was measured by transvaginal sonography. Results Multiple regression analysis demonstrated that cervical length, Bishop score and parity provided independent contribution in the prediction of the likelihood of delivering vaginally within 24 h. Further examination of the different components of the Bishop score showed that only cervical length provided a significant contribution in the prediction of the likelihood of vaginal delivery within 24 h. In the receiver operating characteristic curves, the best cut‐off point for the prediction of successful induction was 28 mm for cervical length and 3 for the Bishop score. However, cervical length appears to be a better predictor than the Bishop score, with a sensitivity of 0.87 and a specificity of 0.71 compared to 0.58 and 0.77, respectively. Similarly, the Kaplan–Meier survival curves indicate that better discriminatory results in the prediction of vaginal delivery within 24 h are achieved using cervical length rather than the Bishop score. Conclusion Transvaginal sonographic measurement of cervical length provides a useful prediction of the likelihood of vaginal delivery within 24 h of induction.Copyright © 2001 International Society of Ultrasound in Obstetrics and Gynecology