Association of inter-delivery interval and the success of vaginal birth after cesarean delivery in high-risk women: a population-based study in the US

Compared to a repeat cesarean section, vaginal birth after cesarean (VBAC) offers potential health benefits. While inter-delivery interval (IDI) may influence VBAC success, its specific impact in high-risk women remains unclear. This population-based cross-sectional study utilized data from the US National Vital Statistics System from 2016 to 2018, including women with a prior cesarean and a current singleton live birth. Univariable and multivariable logistic regression analyses were performed. Among 673,005 high-risk women, 96,479 underwent a trial of labor after cesarean (TOLAC), with 64,167 (66.5%) achieving VBAC. In adjusted analysis, each additional month of IDI was associated with a 0.3% higher odds of VBAC failure (aOR 1.003, 95%CI 1.002–1.003). Using categorical intervals, IDI of 24–59 months and ≥ 60 months were associated with 6.1% (aOR 1.061, 95%CI 1.016–1.108) and 25.9% (aOR 1.259, 95%CI 1.202–1.319) higher odds of failure, respectively, compared to 18–23 months. IDI ≤ 5 or 6–11 months showed no significant association. A longer IDI, particularly ≥ 60 months, is an independent risk factor for VBAC failure among high-risk women.