Objective. To determine the contribution of maternal lipids in predicting large-for-gestational age (LGA) newborns born to women with gestational diabetes mellitus (GDM). Design. Retrospective study. Setting. Yonsei University Health System, Korea. Population. A total of 104 women diagnosed with GDM between January 2000 and June 2008. Methods. Women who were positive on the 50 g oral glucose challenge test (24–28 weeks' gestation) and who were referred patients suspected of GDM underwent a 3 hours, 100 g oral glucose tolerance test for GDM diagnosis. Maternal fasting serum triglycerides and total, high-density lipoprotein (HDL), and low-density lipoprotein cholesterol levels were determined at 24–32 weeks' gestation. Logistic regression analysis was performed to determine maternal parameters independently associated with delivering LGA newborns at term. Main outcome measures. Risk contributions for LGA newborns. Results. Maternal fasting serum triglyceride levels were significantly higher in mothers of LGA newborns compared with other mothers; however, no significant correlations were found between newborn birthweight and maternal fasting glucose, total cholesterol, or HDL cholesterol levels. After adjusting for confounding variables including prepregnancy body mass index, weight gain during pregnancy, age, and parity, maternal hypertriglyceridemia at 24–32 weeks' gestation remained an independent parameter for identifying term LGA newborns. Conclusions. In GDM pregnancies, determining maternal serum triglyceride levels during midpregnancy may help identify women likely to give birth to LGA newborns.