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Background Epidemiologic evidence on the association between infertility and thyroid cancer risk remains inconsistent. We conducted a systematic review and meta-analysis to synthesize available observational evidence and quantify this association. Methods We systematically searched PubMed, Web of Science, and Scopus from inception to February 10, 2026, to identify observational studies evaluating the association between infertility and thyroid cancer risk. Eligible cohort and case–control studies reporting relative effect estimates with 95% confidence intervals (CIs) were included. Summary risk estimates were pooled using random-effects models. Between-study heterogeneity was assessed using the I² statistic. Prespecified subgroup analyses were conducted by sex and study design. Sensitivity analyses and assessments of publication bias were also performed. Results Nine studies met the inclusion criteria, including seven cohort studies and two case–control studies, comprising a total of 4,563,090 participants. In the pooled analysis, infertility was associated with a significantly higher risk of thyroid cancer (relative risk RR, 1.37; 95% CI, 1.15–1.63), with substantial heterogeneity across studies ( I² = 81.9%). Sex-stratified analyses suggested a stronger association among men (RR, 1.53; 95% CI, 1.43–1.65) than among women (RR, 1.31; 95% CI, 1.04–1.66), although the test for interaction was not statistically significant. The findings were robust across sensitivity analyses. Evidence of small-study effects was observed; however, the association remained statistically significant after adjustment using the trim-and-fill method. Conclusions This study suggests that infertility is associated with an increased risk of thyroid cancer. Although substantial heterogeneity was observed, the association remained consistent across multiple sensitivity analyses. However, further well-designed research is needed to verify and clarify this association and its underlying mechanisms.
Qiao et al. (Mon,) studied this question.