Validation of a Prediction Model for Vaginal Birth after Cesarean Delivery Reveals Unexpected Success in a Diverse American Population

Abstract

Objective To investigate the validity of a prediction model for success of vaginal birth after cesarean delivery (VBAC) in an ethnically diverse population. Methods We performed a retrospective cohort study of women admitted at a single academic institution for a trial of labor after cesarean from May 2007 to January 2015. Individual predicted success rates were calculated using the Maternal–Fetal Medicine Units Network prediction model. Participants were stratified into three probability-of-success groups: low (<35%), moderate (35–65%), and high (>65%). The actual versus predicted success rates were compared. Results In total, 568 women met inclusion criteria. Successful VBAC occurred in 402 (71%), compared with a predicted success rate of 66% (p = 0.016). Actual VBAC success rates were higher than predicted by the model in the low (57 vs. 29%; p < 0.001) and moderate (61 vs. 52%; p = 0.003) groups. In the high probability group, the observed and predicted VBAC rates were the same (79%). Conclusion When the predicted success rate was above 65%, the model was highly accurate. In contrast, for women with predicted success rates <35%, actual VBAC rates were nearly twofold higher in our population, suggesting that they should not be discouraged by a low prediction score.

Impact of Gestational Weight Gain on Trial of Labor after Cesarean Success

“…A recent study by Maykin et al found that women with predicted success rates of <35% had actual VBAC rates that were nearly twofold higher and that obesity was not associated with increased TOLAC failures rates. 21 Similarly, our findings suggest that GWG may not have a negative impact on TOLAC success or complications as previously reported. [7][8][9] A potential explanation for our contrasting findings is the fact that previous studies used cohorts from the early 2000s.…”

Limitations of Vaginal Birth After Cesarean Success Prediction

“…In a sample of 568 women undergoing TOLAC in a single academic center, actual success was compared with the SMFM prediction. No differences were found when predictions were 79% or greater, but actual success was nearly double the predicted rate at the lower estimations (29% predicted success vs 57% actual success) …”

“…No differences were found when predictions were 79% or greater, but actual success was nearly double the predicted rate at the lower estimations (29% predicted success vs 57% actual success). 39…”

Considering Labor After Cesarean in a Woman with Class 3 Obesity

“…They calculated predicted VBAC rates for a cohort of 568 women using the Maternal-Fetal Medicine Units Network calculator and compared those calculations with the actual VBAC rates. 20 There was no difference between the predicted and actual VBAC rate for women who were expected to have a high chance of success (79% vs 79%; P = .9989; n = 309). For women (n = 30) for whom the calculator predicted a success rate of less than 35% (mean predicted rate was 29%) the actual VBAC rate was 57% (P = .001), and for women (n = 229) who were expected to have a mean VBAC rate of 52%, the actual rate was 61% (P = .006).…”