Age at Menarche and Risk of Hypertensive Disorders of Pregnancy: A Retrospective Cohort Study

<b>Background/Objectives</b>: Hypertensive disorders of pregnancy (HDP) remain a major contributor to maternal morbidity and mortality worldwide, yet early-life reproductive factors such as age at menarche have been insufficiently explored in relation to HDP. Therefore, we aimed to evaluate the association between age at menarche and the risk of HDP in a cohort of Mexican pregnant women. <b>Methods</b>: We conducted a retrospective cohort study among 1344 women with singleton pregnancies receiving care at a tertiary hospital in Mexico City in 2024. Age at menarche was categorized as <12, 12-14, and >14 years. HDP diagnoses were extracted from clinical records. Poisson regression with robust variance was used to estimate adjusted risk ratios (RRs). Sensitivity analyses included alternative menarche categorizations and restricted cubic spline models. Counterfactual mediation analyses assessed indirect effects through reconstructed prepregnancy BMI and gestational diabetes. <b>Results</b>: Both early (<12 years) and late (>14 years) menarche were associated with higher HDP risk than the 12-14-year reference (adjusted RR = 1.81; 95% CI 1.42-2.30, and 1.74; 95% CI 1.27-2.38, respectively). Spline models confirmed a U-shaped association. Mediation analyses indicated that prepregnancy BMI did not meaningfully mediate the association for either early or late menarche (<5% mediated). Gestational diabetes explained a modest proportion of the association for early menarche (≈14%), but not for late menarche. <b>Conclusions</b>: Age at menarche showed a robust U-shaped association with HDP, mostly independent of adiposity and gestational diabetes, within the limits of the available measurements. Incorporating pubertal timing into routine reproductive history taking may enhance contextual risk assessment for HDP.