Prevalence of hyperthyroidism in infertile women referred to assisted reproductive technology centers affiliated with Urmia University of Medical Sciences: a retrospective cross-sectional study

Background Thyroid dysfunction, particularly hyperthyroidism, is a recognized modulator of female fertility, yet its prevalence among infertile women remains inadequately characterized. This study aimed to determine the prevalence of biochemical hyperthyroidism among infertile women referred to assisted reproductive technology (ART) centers in West Azerbaijan, Iran. Methods In this retrospective cross-sectional study, medical records of 712 infertile women (aged 18–45 years) evaluated between 2020 and 2024 were analyzed. Thyroid function was assessed using serum Thyroid-Stimulating Hormone (TSH) and Free Thyroxine (FT4). The primary outcome was the prevalence of overt biochemical hyperthyroidism (TSH < 0.4 mIU/L with elevated FT4). Secondary outcomes included prevalence of subclinical hyperthyroidism (suppressed TSH with normal FT4) and any suppressed TSH phenotype. Demographic and clinical data were collected. Statistical analyses included descriptive statistics, chi-square tests, t-tests, and binary logistic regression. Results The prevalence of overt hyperthyroidism was 2.8% (95% CI: 1.8–4.2), and subclinical hyperthyroidism was 4.5% (95% CI: 3.2–6.2). Overall, 7.3% of women had suppressed TSH. Women with any suppressed TSH (combined overt and subclinical) were significantly older (33.5 ± 5.1 vs. 31.2 ± 5.8 years, p = 0.004) and more frequently had secondary infertility (59.6% vs. 40.5%, p = 0.031) compared to euthyroid women. Logistic regression confirmed that older age (aOR = 1.07, 95% CI: 1.02–1.13) and secondary infertility (aOR = 2.12, 95% CI: 1.17–3.84) were independently associated with the combined outcome. Conclusion A significant proportion of infertile women had biochemical evidence of thyroid hormone excess, with older age and secondary infertility as key associated factors. These findings may support the benefit of systematic thyroid assessment in women undergoing infertility evaluation.