Study selection
Inclusion criteria were original studies that reported the community-based prevalence of infertility. The following exclusion criteria were applied: (i) irrelevant to prevalence of infertility; (ii) unable to access full text; (iii) editorials, animal studies, conference papers, short newsletters, reviews, conference papers, or brief communications; (iv) conducted in special groups or not population based; (v) unclear or inconsistently applied definitions of infertility; (vi) did not distinguishing infertility from childlessness; (vii) studies that were unclear or no available and numerator denominator. If several publications used the same dataset, the publication that provided the most data was selected.
Duplicated studies were removed from the list of literature retrieved in the first step using Endnote 20.0 software (Clarivate, PA, USA). Second, two reviewers (Zhou and Li) screened the literature independently in two stages: title and abstract screening, full-text retrieval followed by screening according to the inclusion and exclusion criteria. Disagreements were resolved through discussions between the two reviewers, or with the help of a third reviewer (Hao).