Validation of a vaginal birth after cesarean delivery prediction model in women with two prior cesarean deliveries.

Objective: To evaluate whether an existing vaginal birth after cesarean delivery (VBAC) prediction model validated for women with one prior cesarean delivery also accurately predicts the likelihood of VBAC in women with two prior cesarean deliveries.

Methods: We performed a secondary analysis of all women attempting trial of labor after cesarean delivery (TOLAC) with a term singleton pregnancy and two prior cesarean deliveries in the Maternal-Fetal Medicine Units Network (MFMU) Cesarean Registry. Probability of VBAC was calculated for each participant using the MFMU VBAC prediction model. Women were considered to have a recurring indication for cesarean delivery if the indication for either their first or second cesarean delivery was arrest of dilation or descent. A receiver operating characteristic curve was used to assess the classification ability of the model and the predicted likelihood of VBAC success was compared with the actual likelihood using a calibration curve.

Results: Among 369 women with two prior cesarean deliveries undergoing TOLAC, the actual VBAC rate was 66% (95% confidence interval [CI] 61-71). The mean predicted probability of VBAC was higher among women with a successful TOLAC than those with a failed TOLAC (75% compared with 59%, P<.001). The area under the receiver operating characteristic curve for women with two prior cesarean deliveries was 0.74 (95% CI 0.69-0.80). Within deciles of predicted probability greater than 30%, predicted probabilities were similar to and contained actual probabilities within the 95% CI.

Conclusion: The estimates of VBAC success based on the MFMU prediction model are similar to the actual rates observed among women with two prior cesarean deliveries.