PROJECT SUMMARY / ABSTRACT A large volume of research has shown that excessive pregnancy weight gain contributes to maternal postpartum weight retention, child obesity, cesarean delivery, gestational diabetes and preeclampsia, while low gestational weight gain is linked with fetal growth restriction, preterm birth, and perinatal death. However, major gaps remain in our ability to convert these findings into evidence-based recommendations on optimal pregnancy weight gain. The status quo is to evaluate each outcome separately, and without regard to its perceived severity. Further, subjective approaches have been used to select the cut-points of recommended weight gain ranges. Policy-makers urgently need evidence on the optimal range of pregnancy weight gain that considers multiple adverse outcomes simultaneously, accounts for differences in the relative severity of different outcomes, and establishes cut-points using systematic and reproducible methods. In this application, we will develop and apply advanced methodologies that support the creation of robust, evidence-based public health recommendations for weight gain in pregnancy. First, we will generate weights reflecting stakeholder perspectives on the relative severity of competing maternal and child health outcomes associated with gestational weight gain. A Delphi-consensus process will summarize the perceived severity of competing maternal and child health outcomes from diverse panels of 60 women and 60 content experts. Second, we will use a large, diverse cohort of U.S. pregnant women to determine the relationship between gestational weight gain and a composite outcome of adverse events for mothers (preeclampsia, gestational diabetes, cesarean delivery, longer-term obesity, subclinical cardiovascular disease) and children (perinatal death, preterm birth, and small- and large-for-gestational-age birth), with each component weighted to account for its relative severity. Then, we will use our previously-published quantitative approach to identify the optimal range of pregnancy weight gain for women according to different body mass index values, defined as the weight gain associated with the lowest risks of combined, severity-weighted maternal and child outcomes. Successful completion of these aims will provide policy makers with evidence on the complex trade-offs between low and high weight gain on short- and longer-term maternal and child health in order to inform pregnancy weight gain guidelines. Our innovative approach to study multiple adverse outcomes simultaneously and account for their relative severity will enable us to overcome challenges that have previously impeded the synthesis of existing research studies into a systematic, evidence-based weight gain guideline. Our work will impact public health and medical practice by providing high quality evidence for optimizing the nutritional care of pregnant mothers and children.