Our objective was to assess the impact of gestational weight gain (GWG) outside the Institute of Medicine (IOM) recommendations on perinatal outcomes among women with pregestational and gestational diabetes (GDM). We conducted a secondary analysis of the NICHD Consortium on Safe Labor study inclusive of deliveries >23 gestational weeks of non-anomalous singletons with either pregestational diabetes or GDM. The exposure was GWG within (reference), less than, or greater than IOM recommendations for total pregnancy weight gain per pre-pregnancy BMI. Consistent with the 2020 Delphi core outcome set for diabetes in pregnancy, maternal outcomes were cesarean delivery (CD) and preeclampsia, and neonatal outcomes were small for gestational age (SGA, 90th percentile), macrosomia (>4000 g), preterm birth (PTB) <37 weeks, stillbirth, and neonatal death. We used generalized estimating equations, adjusted for age, race, parity, prior CD, chronic hypertension, tobacco use, U.S. region, and delivery year. Of 8,366 deliveries to 8,128 women with pregestational diabetes or GDM, 47% were in excess, 27% within, and 26% less than IOM GWG recommendations. Women with excess GWG were at higher odds of CD (49% vs. 40%; adjusted odds ratios, aOR: 1.58) and preeclampsia (16% vs. 9%; aOR: 1.69), as well as LGA (31% vs. 19%; aOR: 1.97) and macrosomia (18% vs. 9%; aOR: 2.22), but not SGA (5% vs. 8%; aOR: 0.55), compared to those within IOM GWG recommendations. However, women with less GWG were at lower odds of CD (35% vs. 49%; aOR: 0.80), but at higher odds of SGA (10% vs. 8%; aOR: 1.44). GWG was not associated with PTB <37 weeks, stillbirth, and neonatal death. The above associations between GWG and perinatal outcomes persisted when pregestational diabetes and GDM were modeled separately. Women with pregestational and gestational diabetes should be counseled about the increased risk of adverse perinatal outcomes with excess weight gain, in particular CD, preeclampsia, and LGA at birth.View Large Image Figure ViewerDownload Hi-res image Download (PPT)