The growing number of obese women worldwide has many implications for the reproductive health outcomes of mothers and their children. Specifically, prepregnancy obesity has been associated with certain major birth defects. Provided here is a summary of the most recent and comprehensive meta-analysis of reports of associations between prepregnancy obesity and birth defects, along with an update that includes a brief overview of reports of similar associations published since that meta-analysis. The possible reasons for the observed association between prepregnancy obesity and birth defects are explored, and knowledge gaps that suggest possible avenues for future research are highlighted.