Abstract
OBJECTIVES: Women with prepregnancy polycystic ovary syndrome (PCOS) may face higher risks during pregnancy, yet evidence on its link to severe maternal morbidity (SMM) is limited. This population-based study addresses these gaps. DESIGN: This was a population-based cohort study using linked administrative health data from Ontario, Canada. All hospital livebirths and stillbirths 2006-2021, in women aged 15-50 years were included. PARTICIPANTS/MATERIALS, SETTING, METHODS: PCOS was identified using a validated algorithm combining diagnostic codes for PCOS or hirsutism with irregular menses. Among 1,596,228 pregnancies, 110,910 (6.9%) had prior PCOS, diagnosed a median 11 years before delivery. RESULTS: Women with PCOS were older and more often obese. SMM occurred in 2.6 vs. 2.2 per 100 births among women with and without PCOS, respectively (adjusted relative risk 1.10, 95% CI: 1.06-1.15). LIMITATIONS: Limitations include potential residual confounding and misclassification inherent in administrative data. CONCLUSIONS: PCOS confers a modest but significant increase in SMM, underscoring the need for targeted risk assessment and preventive strategies. Awareness of this association may inform clinical risk assessment and management strategies to mitigate serious maternal complications.