Severe Maternal Morbidity by Race and Ethnicity and Birth Mode Among Individuals With a Prior Cesarean Birth.

Importance: Given that nearly one-third of US births are cesarean deliveries, subsequent births after a cesarean delivery are common. Racial and ethnic disparities in severe maternal morbidity (SMM) have been well-documented, and prior studies have identified differences in birth mode after prior cesarean delivery by race and ethnicity. Objective: To examine variation by race and ethnicity in the association between SMM and birth mode for individuals with a prior cesarean delivery. Design, Setting, and Participants: This cross-sectional study used Massachusetts linked birth certificate and hospital discharge data from 2012 to 2021. The analytic sample was limited to births to individuals with 1 prior cesarean delivery. Data were analyzed from August 23, 2024, to March 31, 2025. Exposures: Race and ethnicity and birth mode (vaginal birth after cesarean delivery, planned repeat cesarean delivery, and unplanned repeat cesarean delivery). Main Outcome and Measures: SMM was measured using Centers for Disease Control and Prevention indicators. Associations of race and ethnicity and birth mode with SMM were calculated using logistic regression, then an interaction term was added between race and ethnicity and birth mode. Models controlled for covariates. Results: The study population included 72 836 individuals (mean [SD] age, 32.40, [5.03] years), of whom 8022 (11.0%) were Black, 14 664 (20.1%) were Latinx, and 41 350 (56.8%) were White. Approximately one-third of individuals were born outside the US (25 119 individuals [34.5%]). In adjusted analyses, Black individuals had higher odds of SMM compared with White individuals (adjusted odds ratio [AOR], 1.60; 95% CI, 1.25-2.05). Odds of SMM were higher for unplanned repeat cesarean birth (AOR, 3.05; 95% CI, 2.23-4.18) compared with vaginal birth after cesarean delivery, and higher for planned repeat cesarean birth compared with vaginal birth after cesarean delivery (AOR, 1.57; 95% CI, 1.20-2.06). Including an interaction term identified variation in the association between birth mode and SMM by race and ethnicity. Planned repeat cesarean birth vs VBAC was associated with an increase in the likelihood of SMM of 0.56 (95% CI, 0.21-0.90) percentage points (P = .001) among Black birthing people and 0.46 (95% CI, 0.16-0.76) percentage points (P = .003) among Latinx birthing people, while among White individuals, the likelihood of SMM did not differ between planned repeat cesarean birth and VBAC. Conclusions and Relevance: In this cross-sectional study of births among individuals with a prior cesarean birth, patterns of SMM by birth mode varied by race and ethnicity, with elevated rates of SMM among those from marginalized racial and ethnic groups with planned cesarean births. Future work should identify interventions to improve quality of care and promote equity for this population.