Body mass index outperforms the Rotterdam criteria in defining phenotypic heterogeneity in polycystic ovary syndrome: a multicenter study from the Italian PCOS registry (PCOSOUTCOME.net)

Purpose: Polycystic ovary syndrome (PCOS) is a common and highly heterogeneous endocrine-metabolic disorder. The Rotterdam criteria identify four diagnostic phenotypes; however, it remains unclear whether these phenotypes or body mass index (BMI) better predict metabolic risk. The PCOSOUTCOME.net registry collects data from multiple Italian centers and provides an opportunity to compare the effectiveness of Rotterdam phenotypes versus BMI in characterizing the clinical, metabolic, and psychological heterogeneity of women with PCOS. Methods: We included 1,314 Caucasian women of reproductive age with PCOS. Participants were stratified according to Rotterdam phenotypes and BMI categories (normal weight, overweight, and obesity; and BMI < 27 kg/m² vs. ≥ 27 kg/m²). Clinical, hormonal, metabolic, gynecological, and psychological parameters were assessed and compared across subgroups. Results: No significant differences in BMI or in the prevalence of metabolic complications (dyslipidemia, glucose intolerance, hypertension, and metabolic syndrome) were observed among the four Rotterdam phenotypes, although anxiety scores were highest in phenotype A. In contrast, BMI-based stratification identified clear differences in metabolic markers: women with obesity or a BMI ≥ 27 kg/m² showed a higher prevalence of all metabolic complications, as well as higher free androgen index (FAI) and hirsutism scores. Conclusions: In this multicenter cohort, Rotterdam phenotypes failed to discriminate metabolic risk, whereas BMI-based stratification proved more informative in identifying cardiometabolic complications. Moreover, obesity in PCOS identifies a distinct hyperandrogenic phenotype. These findings underscore the need to integrate BMI into the classification of PCOS to better capture patient heterogeneity, with potential implications for metabolic assessment and risk stratification.