Transvaginal sonographic measurement of cervical length vs. Bishop score in labor induction at term: tolerability and prediction of Cesarean delivery.

OBJECTIVES

To compare transvaginal sonography for cervical length measurement and digital examination for Bishop score assessment in women undergoing labor induction at term, to assess their tolerability (in terms of pain) and ability to predict need for Cesarean delivery.

METHODS

A prospective study was performed on 249 women admitted for labor induction. Cervical length was measured using transvaginal ultrasound examination. A 10-point visual analog scale (VAS) for procedure-related pain was obtained. Bishop score was determined just before labor induction and another pain score was obtained. Delivery outcome was recorded. Analyses were by t-test, Fisher's exact test, receiver-operating characteristics (ROC) curves and multivariate logistic regression.

RESULTS

Transvaginal sonography was significantly less painful than digital examination for Bishop score assessment (mean difference in VAS score 3.46; P<0.001). Analyses of the ROC curves for cervical length and Bishop score indicated that both were predictors of Cesarean delivery (area under the curve 0.611 vs. 0.607; P=0.012 vs. P=0.015, respectively) with optimal cut-offs for predicting Cesarean delivery of >20 mm for cervical length and Bishop score<or=5. Cervical length had superior sensitivity (80% vs. 64%) and marginally better positive (30% vs. 27%) and negative (89% vs. 83%) predictive values. Multivariate logistic regression analysis revealed that only nulliparity (adjusted odds ratio (AOR) 4.1; 95% CI, 2.1-8.1; P<0.001) and transvaginal sonographic cervical length>20 mm (AOR 3.4; 95% CI, 1.4-8.1; P=0.006) were independent predictors of Cesarean delivery.

CONCLUSIONS

Transvaginal sonography for cervical length measurement is better tolerated than digital examination for Bishop score assessment. Both cervical length and Bishop score are useful predictors of the need for Cesarean delivery following labor induction. A cervical length>20 mm at labor induction at term is an independent predictor of Cesarean delivery.