Endometriosis and Adverse Pregnancy Outcomes: A Dual-Cohort Study of Over 4 Million California Births

Abstract Although endometriosis is increasingly recognized as a risk factor for adverse pregnancy outcomes, large-scale analyses in U.S. populations remain limited. In this retrospective dual-cohort study, we analyzed over 4 million singleton births in California (2011–2020) and a complementary academic electronic medical record (EMR) dataset to evaluate adverse pregnancy outcomes in individuals with endometriosis. Adjusting for use of assisted reproductive technology, prenatal care, and comorbidities, we found consistent significant associations between endometriosis and placenta previa (aRR 4.9, 95% CI 4.4 to 5.4), placental abruption (aRR 1.9, 95% CI 1.6 to 2.3), preterm birth (aRR 1.5, 95% CI 1.4 to 1.6), hypertensive disorders of pregnancy (aRRs 1.3–1.4, 95% CI 1.1 to 1.5), gestational diabetes (aRR 1.2, 95% CI 1.1 to 1.3), cesarean delivery (aRR 1.6, 95% CI 1.6 to 1.7), and severe maternal morbidity (aRR 2.3, 95% CI 2.1–2.6). Findings were directionally consistent across both population-level and institutional cohorts, supporting the robustness of observed associations. This underscores the systemic impact of endometriosis beyond conception and calls for its integration into pregnancy risk assessment models. We also demonstrate the ability to leverage two complementary data sources (birth records and EMR) to better understand relationships and outcomes in reproductive health. Recognizing endometriosis as a chronic condition with obstetric consequences may offer new avenues for prevention and early intervention to improve maternal, fetal, and neonatal outcomes.