Strengths and limitations
This study has several advantages: (i) The strengths of this study
include the comprehensive search strategies, a double review process,
and stringent selection criteria. The study also used a standardized
tool to evaluate the quality of the literature. (ii) In our systematic
review, we included only studies that were conducted in the
community-based population so that our results could be more accurate
and representative. (iii) We strictly limited the definition of
infertility in our study to ensure the comparability of the combined
prevalence. The standardized definitions of infertility subtypes and an
adequate subgroup analysis reduced heterogeneity.
Several limitations of this study should also be recognized. First,
although we unified the definitions of the prevalence of infertility and
its subtypes before pooling the prevalence estimates, substantial
heterogeneity was detected. Besides, even for the prevalence of
infertility, for which the contributing data points successfully covered
all the 6 WHO regions, the prevalence estimation at the regional level
was not optimal given that more than half of the included studies were
concentrated in only 2 regions (Asian Region and European Region), and
the small number of studies in some countries which may not represent
the true estimate in that countries.