Objective To compare the ability of customized versus normalized population fetal growth norms in identifying neonates at risk for adverse perinatal outcomes (APOs) associated with fetal overgrowth and gestational diabetes (GDM). Study Design Secondary analysis of a multicenter treatment trial of mild GDM. The primary outcome was a composite of neonatal outcomes associated with fetal overgrowth and GDM. Birth weight percentiles were calculated using ethnicity- and gender-specific population and customized norms (Gardosi). Results Two hundred three (9.8%) and 288 (13.8%) neonates were large for gestational age by population (LGApop) and customized (LGAcust) norms, respectively. Both LGApop and LGAcust were associated with the primary outcome and neonatal hyperinsulinemia, but neither was associated with hypoglycemia or hyperbilirubinemia. The ability of customized and population birth weight percentiles for predicting APOs were poor (area under the receiver operating characteristic curve < 0.6 for six of eight APOs). Conclusion Neither customized nor normalized population norms better identify neonates at risk of APOs related to fetal overgrowth and GDM. © 2013 by Thieme Medical Publishers, Inc.