When's it best to attempt VBAC?

While women who have had a prior cesarean section can safely attempt vaginal delivery beyond their estimated due date, they are 36% more likely to fail than women who attempt vaginal delivery prior to 40 weeks' gestation.

Researchers conducted a 5-year retrospective cohort study in 17 university and community hospitals of 11,587 women who had at least one prior C/S delivery. They calculated that the increased risk of a failed vaginal birth after a previous C/S delivery at more than 40 weeks' gestation was 31.3% compared with 22.2% prior to 40 weeks (OR 1.36, 95% CI; 1.24–1.50). The risk increasedto 35.4% compared with 24.3% (OR 1.35, 95% CI; 1.20–1.53) when the group was limited to 41 gestational weeks or more. There were no significant increases in the risks of uterine rupture or overall morbidity.

Coassolo KM, Stamilio DM, Pare E, et al. Safety and efficacy of vaginal birth after cesarean attempts at or beyond 40 weeks of gestation. Obstet Gynecol. 2005;106:700-706.