Background/Objectives: 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. Methods: 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 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. Results: Both early (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. Conclusions: 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.

Early menarche has been recognized as an early-life marker of metabolic vulnerability, yet its link to gestational diabetes mellitus (GDM) remains unclear. We investigated this association in a retrospective case–control study of 71 cases and 355 controls from a tertiary hospital in Mexico City. Age at menarche was evaluated both in categories and using restricted cubic splines to capture potential non-linear trends. Mediation analysis explored the contribution of pregestational body mass index (BMI) to the relationship between variables. Women who experienced menarche before age 12 had more than twice the odds of developing GDM compared with those whose menarche occurred between 12 and 15 years (adjusted OR = 2.51, 95% CI 1.40–4.50). In contrast, late menarche showed a minor, non-significant increase in risk. The spline models revealed a subtle U-shaped pattern, suggesting that both very early and delayed pubertal timing may carry metabolic disadvantages. The mediation analysis showed that pregestational BMI accounted for only a minor share of this association. Overall, the findings indicate that early pubertal onset may influence glucose regulation during pregnancy through pathways beyond adiposity, highlighting early menarche as a valuable marker for identifying women at higher risk of GDM.