Validation of the Prediction Model for Success of Vaginal Birth after Cesarean Delivery in Japanese Women

Aim: To validate a previously developed prediction model for vaginal birth after cesarean (VBAC) using a Japanese cohort. Methods: We performed a cohort study of all term pregnant women with a vertex position, singleton gestation, and one prior low transverse cesarean delivery attempting a trial of labor between April 1985 and March 2010. Variables necessary for the prediction of successful VBAC were maternal age, pre-pregnancy body mass index, ethnicity, prior vaginal delivery, prior VBAC, and indication for prior cesarean delivery. They were extracted from medical records and put into the formula that calculates an individual woman's predicted VBAC success rate. The predicted rates were then partitioned into deciles and compared with the actual VBAC rates. The predictive ability of the model was assessed with a receiver operating characteristic and the area under the curve (AUC) was determined. Results: Seven hundred and twenty-five women who met the inclusion criteria had complete data available, of which 664 (91.6%) had VBAC. The predicted probability of VBAC, as calculated by the regression equation, was significantly higher in those who had a successful trial of labor (median 80.1%, interquartile range 71.5-88.7) than those who did not (median 69.4%, interquartile range 59.9-78.9, P<0.001). The predictive model had AUC of 0.80, which was comparative to the originally described one. When the predicted rates were each deciles of over 70%, the actual success rates were more than 90%. Conclusion: The previously published prediction model for VBAC developed in the USA is also available to Japanese women.