Pregestational diabetes: A risk factor for vaginal birth after cesarean section failure?

Vaginal birth after cesarean delivery (VBAC) failure is associated with perinatal morbidity. The ability to predict VBAC failure in subgroups of high-risk women is important. Our objectives were: (1) to estimate if women with pregestational diabetes (PDM) who attempt VBAC are at increased risk of failure, and (2) to identify clinical characteristics of PDM women associated with failure. We performed a retrospective cohort study of women eligible for VBAC, delivered between 1995 and 1999 at 17 hospitals to study maternal history/outcomes and neonatal outcomes ascertained through chart abstraction. Women with gestational diabetes were excluded. Student t test was used to compare continuous characteristics. Chi-square/Fisher exact tests were used to compare categorical variables. Multivariable logistic regression analysis was used to control for confounders. Of all eligible women (23,601), 37% of diabetics (n=127) and 56% of nondiabetics (n=12968) attempted VBAC. The VBAC failure rate for PDM was 38% versus 24% for nondiabetic women (p<0.001). The risk of failure for PDM patients was increased after controlling for confounders (adjusted odds ratio 1.61, 95% confidence interval 1.06 to 2.51; p=0.038). PDM is independently associated with VBAC failure. The success rate for women with PDM who attempted VBAC (62%) is at the lower end of the general published VBAC success rate range.