Santos S, et al. - Performing individual participant data meta-analysis of 39 cohorts, maternal pre-pregnancy BMI and gestational weight gain were assessed separately or in combination for their associations with the risks of pregnancy complications and their population impact. Findings support the association of maternal pre-pregnancy BMI and gestational weight gain, across their full ranges, with the risks of pregnancy complications. The highest risk of pregnancy complications was observed for obese mothers with high gestational weight gain. The burden of pregnancy complications and ultimately the risk of maternal and neonatal morbidity could be reduced via promoting a healthy pre-pregnancy BMI and gestational weight gain.