Mode of Birth and Stroke Risk After Childbirth Among Women With Moyamoya Disease.

Importance: There is limited large-scale evidence to guide the optimal mode of birth for patients with moyamoya disease (MMD). Objective: To evaluate whether the mode of birth (cesarean vs vaginal) is associated with stroke risk after childbirth for women with MMD. Design, Setting, and Participants: This cohort study evaluated stroke outcomes up to 3 years after childbirth. A nationwide, population-based analysis was performed using data from the Health Insurance Review and Assessment Service of South Korea. Individuals with MMD from January 1, 2002, to December 31, 2023 were identified. Among 31 750 patients, those with birth-related procedure codes were selected. The study population was restricted to women aged 19 to 49 years, and those with a diagnosis of malignant neoplasm within 3 years before the index date (date of childbirth) were excluded. Data were analyzed from June 11 to September 8, 2025. Exposure: Mode of birth. Main Outcomes and Measures: The primary outcome was any stroke, defined as a composite of ischemic or hemorrhagic stroke. Secondary outcomes included ischemic stroke, hemorrhagic stroke, and transient ischemic attack. Results: Of 1683 women analyzed (mean [SD] age, 33.6 [7.8] years), 1077 (64.0%) had cesarean births, and 606 (36.0%) had vaginal births. Post partum (3 months), any stroke incidence was 63.49 and 33.33 per 1000 person-years for cesarean and vaginal births, respectively. Multivariable analyses showed no significant risk differences for any stroke by birth mode at 3 months (adjusted hazard ratio [aHR], 0.71 [95% CI, 0.26-1.97]; P = .52) or 3 years (aHR, 0.90 [95% CI, 0.55-1.47]; P = .67). A significant interaction was observed between the mode of birth and the clinical onset type of MMD for the risk of any stroke (interaction P = .04 after Bonferroni correction); the adjusted HR for vaginal vs cesarean birth was 0.10 (95% CI, 0.01-0.79) in the asymptomatic or nonvascular onset subgroup, 1.49 (95% CI, 0.73-3.03) in the ischemic onset subgroup, and 0.94 (95% CI, 0.50-1.77) in the hemorrhagic onset subgroup. Notably, stroke incidence peaked in the early postpartum period (≤6 months: 35.7 per 1000 person-years), decreased at 1 year, and thereafter remained at a similar level. Conclusions and Relevance: In this cohort study of women with MMD, MMD itself was not found to be an absolute indication for cesarean birth; birth planning should be individualized based on obstetric factors and clinical onset type rather than routine preference for cesarean birth. In addition, vigilant monitoring and preventive strategies during the early postpartum period are warranted.