<b>Association of BMI With Estrogen–Progesterone Imbalance and Menstrual Irregularity in Obese Women: Cross-Sectional Analytical Evidence From 80 Participants</b>

Background: Obesity is a major determinant of reproductive dysfunction, exerting adverse effects on hypothalamic–pituitary–ovarian axis function and ovarian steroidogenesis. Excess adiposity increases peripheral aromatization of androgens into estradiol while impairing luteal progesterone production, creating a hormonal imbalance that predisposes to menstrual irregularity. Despite evidence from Western populations, data from South Asia remain limited, where women are prone to visceral adiposity and metabolic risk at lower BMI thresholds. Objective: This study aimed to examine the association between body mass index, estradiol and progesterone imbalance, and menstrual irregularity in obese women, and to assess how gradients of BMI class correspond with reproductive risk. Methods: A cross-sectional analytical study was conducted among 80 obese women aged 18–45 years in Sialkot, Pakistan. Participants were classified into BMI classes I–III, and menstrual history was obtained through structured interviews. Serum estradiol and progesterone were measured using standardized immunoassays. Group differences were assessed using ANOVA, Kruskal–Wallis, and chi-square tests, while linear and logistic regression models evaluated continuous associations and adjusted odds of menstrual irregularity, controlling for age, diabetes, thyroid disorder, and physical activity. Results: Menstrual irregularity increased progressively with BMI, affecting 25.0% of class I, 40.7% of class II, and 72.0% of class III women (p < 0.001). Estradiol rose from 92.1 to 178.2 pg/mL across classes, while progesterone declined from 5.4 to 0.8 ng/mL. Low progesterone prevalence increased from 14.3% to 60.0%, and high estradiol from 7.1% to 36.0%. Each 5 kg/m² rise in BMI increased estradiol by 27.4 pg/mL and reduced progesterone log-values by 0.42 units. In multivariable models, class III obesity was associated with a 6.5-fold higher risk of menstrual irregularity compared with class I (p = 0.01). Conclusion: Higher BMI in obese women is strongly linked to an estrogen–progesterone imbalance and a greater likelihood of menstrual irregularity, with risks escalating across obesity classes. These findings emphasize the need for BMI stratification and dual hormone profiling in clinical assessment and call for interventional studies targeting weight reduction and hormonal restoration to improve reproductive outcomes