OBJECTIVE -To determine the contribution of maternal glucose and lipids to intrauterine metabolic environment and fetal growth in pregnancies with gestational diabetes mellitus (GDM).RESEARCH DESIGN AND METHODS -In 150 pregnancies, serum triglycerides (TGs), cholesterol, free fatty acids (FFAs), glycerol, insulin, and glucose were determined in maternal serum and cord blood during the 3rd trimester. Maternal glucose values came from oral glucose tolerance testing and glucose profiles. Measurements of fetal abdominal circumference (AC) were performed simultaneously with maternal blood sampling and birth weight, and BMI and neonatal fat mass were obtained following delivery.RESULTS -Maternal TGs and FFAs correlated with fetal AC size (at 28 weeks: triglycerides, P ϭ 0.001; FFAs, P ϭ 0.02), and at delivery they correlated with all neonatal anthropometric measures (FFA: birth weight, P ϭ 0.002; BMI, P ϭ 0.001; fat mass, P ϭ 0.01). After adjustment for confounding variables, maternal FFAs and TGs at delivery remained the only parameters independently related to newborns large for gestational age (LGA) (P ϭ 0.008 and P ϭ 0.04, respectively). Maternal FFA levels were higher in mothers with LGA newborns than in those with appropriate for gestational age (AGA) newborns (362.8 Ϯ 101.7 vs. 252.4 Ϯ 10.1, P ϭ 0.002). Maternal levels of TGs, FFAs, and glycerol at delivery correlated with those in cord blood (P ϭ 0.003, P ϭ 0.004, and P ϭ 0.005, respectively). Fetal triglyceride and cholesterol levels were negatively correlated with newborn birth weight (P ϭ 0.001), BMI (P ϭ 0.004), and fat mass (P ϭ 0.001). TGs were significantly higher in small for gestational age (SGA) newborns compared with AGA or LGA newborns, while insulin-to-glucose ratio and FFAs were the highest in LGA newborns.CONCLUSIONS -In well-controlled GDM pregnancies, maternal lipids are strong predictors for fetal lipids and fetal growth. Infants with abnormal growth seem to be exposed to a distinct intrauterine environment compared with those with appropriate growth.