Intrauterine growth restriction (IUGR) remains a major problem for both human health and animal production due to its association with high rates of neonatal morbidity and mortality, low efficiency of food utilization, permanent adverse effects on postnatal growth and development, and long-term health and productivity of the offspring. However, the underlying mechanisms for IUGR are largely unknown. In this study, one IUGR fetus and one normal body weight (NBW) fetus were obtained from each of 9 gilts at each of 2 gestational ages (d 90 and 110). Metabolomes of umbilical vein plasma in IUGR and NBW fetuses were determined by MS, while hormones, amino acids, and related metabolites in maternal and fetal plasma were measured using assay kits and chromatographic methods. Metabolites (including glucose, urea, ammonia, amino acids, and lipids) in umbilical vein plasma exhibited a cluster of differences between IUGR and NBW fetuses on d 90 and 110 of gestation. These changes in the IUGR group are associated with disorders of nutrient and energy metabolism as well as endocrine imbalances, which may contribute to the retardation of fetal growth and development. The findings help provide information regarding potential mechanisms responsible for IUGR in swine and also have important implications for the design of effective strategies to prevent, diagnose, and treat IUGR in other mammalian species, including humans. J. Nutr. 142: 990-998, 2012.