Prevalence of anti-thyroid peroxidase antibodies among women with polycystic ovary syndrome

Shared genetic, environmental, metabolic, and immunological factors may underlie both polycystic ovary syndrome (PCOS) and autoimmune thyroid disease (AITD), suggesting a potential causal association between the two conditions. This study aimed to evaluate the prevalence of AITD in women with PCOS compared to age-matched controls. A total of 1047 women diagnosed with PCOS based on the Rotterdam criteria and 1047 age-matched control women attending the Infertility Research and Clinical Center in Yazd, Iran, were enrolled. Detailed medical histories were obtained from all participants. Anthropometric measurements, hormonal profiles, and thyroid function tests were assessed. Women with PCOS exhibited significantly higher serum anti-thyroid peroxidase antibody (anti-TPO Ab) levels than controls. The median (interquartile range) anti-TPO Ab level was notably higher in PCOS patients (e.g., 12.0 [4.0-45.0] IU/mL) than in controls (4.0 [1.0-20.0] IU/mL; p = 0.002). No significant difference in serum thyroid-stimulating hormone (TSH) concentrations was observed between the groups, although TSH tended to be higher in PCOS (p = 0.073). AMH levels were significantly elevated in the PCOS group. Anti-TPO antibodies were positive in 135 of 1047 women with PCOS (12.89%). Among PCOS patients, those who were anti-TPO positive had lower BMI (mean 26.24 vs 27.65 kg/m²; p = 0.004) and lower TSH (mean 2.89 vs 3.45 mIU/L; p = 0.010) than AITD-negative patients. In multivariable logistic regression (complete-case, n = 784), higher BMI (adjusted OR per 1 kg/m² = 0.944; 95% CI 0.904-0.986; p = 0.0098) and higher AMH (adjusted OR per 1 ng/mL = 0.937; 95% CI 0.883-0.995; p = 0.033) were associated with lower odds of anti-TPO positivity; age, TSH, and prolactin were not significant. Women with PCOS exhibit a higher prevalence of AITD compared to those without PCOS. These findings underscore the importance of screening for anti-TPO antibodies and assessing TSH in PCOS patients, even in the absence of overt thyroid dysfunction. The borderline TSH observed (p = 0.073) suggests a possible trend toward thyroid axis alteration in PCOS.