Data extraction and risk of bias assessment
The items of each eligible study were extracted by two reviewers (Zhou and Li), including the first author, year of publication, year of investigation, study settings, research type, study population, sample size, definition of infertility, and prevalence of infertility and subtypes (primary and secondary). In parallel, the two reviewers assessed the relevant studies using the 10-item Hoy risk of bias tool (Table S2), designed for prevalence studies. Each item was rated on a dichotomous scale, with 1 indicating low risk of bias and 0 indicating high risk of bias. An overall score was calculated for each study as the mean score of the two reviewers, ranging from 0 to 10, with a score of at least 9 indicating a low risk of bias, 7–8 indicating a moderate risk, and less than 7 indicating a high risk. We calculated inter-rater reliability using the kappa coefficient for each item (Table S3).