Objective: To compare pre-induction ultrasonographic cervical length and Bishop score in predicting risk of caesarean section after labor induction with prostaglandins.
Patients and methods: Assessment of the Bishop score and measurement of the cervical length by transvaginal sonography were performed by two operators, blinded to each other's results among women with singleton pregnancies at between 34(+0) - 41(+3) weeks of gestation requiring induction of labor with prostaglandins for medical indications. Fisher's exact test and regression logistic models were used for statistics analysis. In order to measure the strength of the association between ultrasonographic cervical length or Bishop score on one hand, and the caesarean sections rate (global or for failed induction or failure to progress) on the other hand, we computed odds ratios with 95% confidence interval.
Results: Among the 266 patients included in the study, multivariate analysis has shown that only Bishop score was predictive for the global caesarean section risk (OR [95% CI] 0.63 [0.45-0.87] ; P =0.005). However, neither Bishop score (OR [95% CI] 0.68 [0.42-1.09] ; P =0.11), nor ultrasonographic cervical length (OR [95% CI] 1.01 [0.95-1.08] ; P =0.59) was predictive for failed induction or failure to progress caesarean section risk.
Discussion and conclusion: The Bishop score appears to be a better predictor of the global caesarean section risk than ultrasonographic cervical length after induction of labor for medical reasons.