Validation of a prediction model for vaginal birth after caesarean

Pregnant women with a previous Caesarean section face making the decision to undergo an elective repeat Caesarean section or to attempt a trial of labour with the goal of achieving a vaginal birth after Caesarean (VBAC). One of the key factors in counselling these women is the probability of a successful VBAC. We aimed to validate a prediction model for VBAC success.

We performed an analysis of women at term with one prior low-transverse Caesarean section and a live cephalic singleton pregnancy who attempted a trial of labour after Caesarean (TOLAC) at 32 hospitals in Quebec between 2008 and 2012. The individual TOLAC probabilities of success were calculated without regard to ethnicity, using a prediction model previously developed in the United States. The predictive ability of the model was assessed using receiver operating characteristic curves and the area under the curve (AUC). In addition, a calibration curve was generated by plotting the predicted and observed VBAC rates.

Of 3113 eligible women who underwent TOLAC, we found an overall rate of VBAC of 75.3%. Beyond a predicted probability of 40%, both observed and predicted TOLAC success rates were similar. The accuracy of the model was high (AUC = 0.72; 95% CI 0.70 to 0.74, P < 0.001) as was the correlation between observed and predicted probabilities of TOLAC success (R² = 0.98). Finally, for women requiring induction of labour, observed and predicted probabilities were similar for a predicted probability ≥ 70%.

It is possible to estimate VBAC success accurately in Quebec using a validated prediction model from the United States. This model may be used in practice without regard to ethnicity as a primary method to refine counselling during antepartum visits for women with a prior Caesarean section.