(666) Parity and Prior VBAC in Relation to Uterine Rupture Risk During TOLAC

We conducted a retrospective cohort study of 9,597 women with a single prior cesarean delivery who attempted TOLAC at a tertiary medical center between 2011–2023. Multivariable logistic regression models were used to assess the association between increasing parity, prior VBAC, and uterine rupture risk, adjusting for induction of labor, birthweight, maternal age, and other potential confounders.

Results:
Overall, 38 uterine ruptures occurred (0.4%). Increasing parity was significantly associated with lower odds of uterine rupture (adjusted OR 0.78, 95% CI 0.62–0.97, p=0.026). Similarly, a history of prior VBAC was protective when assessed individually (unadjusted OR 0.67, 95% CI 0.52–0.86, p< 0.001). However, when parity and prior VBAC were included in the same multivariable model, only parity remained statistically significant (adjusted OR 0.78, 95% CI 0.62–0.97), while prior VBAC was no longer independently associated with reduced rupture risk (adjusted OR 0.76, 95% CI 0.55–1.05, p=0.093). Induction of labor was independently associated with a higher rupture risk (adjusted OR 3.12, 95% CI 1.60–6.08). Neither birthweight nor maternal age were significantly associated with uterine rupture.

Conclusion:

Increasing parity is independently associated with a reduced risk of uterine rupture during TOLAC, whereas prior VBAC, although protective in unadjusted analyses, does not retain independent significance after adjustment. These findings suggest that the protective effect of prior vaginal delivery is largely explained by higher parity rather than VBAC status alone, which may improve counseling and risk stratification for women planning TOLAC.