Introduction Maternal obesity is associated with an increased risk for adverse perinatal outcomes. Obesity is also associated with a chronic inflammatory state and metabolic derangements that affect the newborn. The additional use of cardiopulmonary bypass during the neonatal period could impact the systemic inflammatory response in the immediate postoperative period that manifests as cardiac depression and multi-organ dysfunction. This study aimed to determine the association of maternal obesity and excessive weight gain during pregnancy with the immediate postoperative morbidity of neonatal patients undergoing cardiopulmonary bypass.A retrospective review of neonates who underwent cardiopulmonary bypass within the first 30 days of life at our institution between 2011 and 2013 was conducted. Postoperative variables investigated included the duration of length of mechanical ventilation, length of stay in the ICU, peak vasoactive inotrope scores, and peak lactate level. Maternal obesity was defined as 1st trimester body mass index ⩾30 kg/m2. Excessive weight gain was defined as ⩾12 kg gained during pregnancy. In order to determine the association between maternal obesity or excessive weight gain and postoperative variables, we used multiple linear regression, adjusting for birth weight and risk adjustment for congenital heart surgery score.Records from 58 mother-baby dyads were examined. After controlling for birth weight and risk adjustment for congenital heart surgery score, there were no significant associations between maternal obesity and excessive weight gain during pregnancy versus all postoperative outcomes measured.Despite the known negative impact of maternal obesity on perinatal outcomes, we were unable to find associations between maternal obesity and excessive weight gain during pregnancy versus postoperative outcomes.