(126) Success of Vaginal Birth after Cesarean (VBAC) Following Induced Versus Spontaneous Labor

Objective: To evaluate characteristics associated with vaginal birth after cesarean (VBAC) success in women undergoing induction of labor (IOL).

Study Design: Passive prospective cohort of singleton pregnancies with a history of one or two prior Cesareans undergoing a trial of labor after Cesarean (TOLAC) following IOL and spontaneous labor ≥ 36 weeks at a tertiary care center (2011-2022), retrospectively analyzed. We assessed univariate associations between pregnancy characteristics and 1) form of TOLAC onset (spontaneous versus induced) & 2) VBAC outcome (success / failure). Factors with P < .2 on one or both univariate analyses were considered for incorporation into a multivariable model predictive of VBAC.

Results: Of 1434 individuals undergoing TOLAC, 919/1242 (74%) who met inclusion criteria had VBAC - 405/625 (65%) following induction vs 514/617 (83%) spontaneous labor, P < .0001. Some characteristics were similar between groups but the IOL group was slightly older and had a higher BMI, later gestational age, and lower modified Bishop scores at time of TOLAC (Table 1). Fewer undergoing IOL had a prior VBAC. More had gestational weight gain in excess of guidelines, hypertension, and diabetes. 13 factors were independently associated with odds of VBAC on multivariable analysis (Figure 1). IOL for preeclampsia was independently associated with lower odds of VBAC but IOL that was elective or for another indication was not (aOR0.78, 95% CI 0.53-1.14). The 15-covariate model (Figure 1) had an optimism-corrected bootstrapped (1000 replicates) AUROC of 0.78 (95% CI 0.74-0.80).

Conclusion: As compared to IOL, a higher proportion of pregnancies with spontaneous labor had VBAC. However, after adjustment of relevant clinical factors associated with VBAC success, only IOL for preeclampsia was found to be independently associated with failed TOLAC, while elective IOL and IOL for other indications was not.