TNF and polycystic ovary syndrome: Study design: Observational studies (cross-sectional, case-control, cohort baseline comparisons) from hospital-based or community-based settings and peer-reviewed original articles in English published between January 1, 2014, and August 2025 that compared circulating TNF-α levels in women with PCOS and non-PCOS controls and provided extractable quantitative data were included.