Adverse Pregnancy Outcomes and Risk of Subarachnoid Hemorrhage: A 50-Year Population-Based Cohort Study in Sweden

BACKGROUND: Adverse pregnancy outcomes (APOs) are increasingly recognized as early indicators of maternal cardiovascular risk. However, their associations with nontraumatic subarachnoid hemorrhage (SAH) remain poorly understood. METHODS: We conducted a nationwide cohort study of 1 785 088 primiparous women in the Swedish Medical Birth Register between 1973 and 2014, followed from first birth through December 31, 2023. APOs included hypertensive disorders of pregnancy, gestational diabetes, placental abruption, preterm birth, abnormal fetal growth, and stillbirth. SAH was the primary outcome, with aortic aneurysm rupture or dissection and spontaneous coronary artery dissection as secondary outcomes. Hazard ratios (HRs) and 95% CIs were estimated using Cox regression, adjusting for calendar year, parity, maternal sociodemographic characteristics, and psychiatric disorders, with sibling analyses to account for shared familial and genetic factors. RESULTS: Mean maternal age was 28.2 years, and abnormal fetal growth was the most common APO category. Over up to 50 years, 759 722 (42.6%) women experienced at least 1 APO; there were 5751 (0.32%) events of SAH. Women with APOs had increased risks of SAH compared with those without, particularly after placental abruption (HR, 1.62 [95% CI, 1.29-2.04]), hypertensive disorders of pregnancy (HR, 1.58 [95% CI, 1.41-1.77]), gestational diabetes (HR, 1.40 [95% CI, 1.04-1.90]), preterm birth (HR, 1.35 [95% CI, 1.24-1.47]), and small for gestational age (HR, 1.34 [95% CI, 1.26-1.43]). The associations were consistent in sibship analyses. The excess SAH risk was greatest in the first years after delivery and attenuated over time. Increased risks of aortic aneurysm rupture or dissection were observed after hypertensive disorders of pregnancy, preterm birth, and severely large for gestational age (HRs ranged from 1.43 to 1.66), whereas associations with spontaneous coronary artery dissection differed in direction. CONCLUSIONS: APOs were associated with increased maternal risk of SAH, with variation by the timing, severity, and accumulation of pregnancy complications, suggesting underlying vascular vulnerability.