TNF and polycystic ovary syndrome: Subgroup analyses were also performed according to 1) BMI, 2) diagnostic definitions applied, 3) assay method, and 4) country. To assess whether obesity status influenced TNF-α levels in PCOS, studies were stratified according to the mean BMI of PCOS cohorts: lean (mean BMI < 25 kg/m2) and obese (mean BMI ≥ 25 kg/m2).