Infant macrosomia is a classic feature of a gestational diabetes mellitus (GDM) pregnancy and is associated with increased risk of adult obesity and type II diabetes mellitus, however mechanisms linking GDM and later disease remain poorly understood. The heterozygous leptin receptor-deficient (Lepr db/Ļ© ) mouse develops spontaneous GDM and the fetuses display characteristics similar to infants of GDM mothers. We examined the effects of GDM on maternal insulin resistance, fetal growth, and postnatal development of hepatic insulin resistance. Fetal body weight on d 18 of gestation was 6.5% greater (p Ļ½ 0.05) in pups from ad libitum-fed db/Ļ© mothers compared with wild-type (WT) controls. Pair-feeding db/Ļ© mothers to the intake of WT mothers normalized fetal weight despite less than normal maternal insulin sensitivity. More stringent caloric restriction reduced insulin and glucose levels below WT controls and resulted in fetal intrauterine growth restriction. The level of hepatic insulin receptor protein was decreased by 28% to 31% in both intrauterine growth restriction and fetuses from ad libitum-fed GDM mothers compared with offspring from WT mothers. In 24-wkold adult offspring from GDM mothers, body weight was similar to WT offspring, however, the females from GDM mothers were fatter and hyperinsulinemic compared with offspring from WT mothers. Insulin-stimulated phosphorylation of Akt, a key intermediate in insulin signaling, was severely decreased in the livers of adult GDM offspring. Hepatic glucose-6-phosphatase activity was also inappropriately increased in the adult offspring from GDM mothers. These results suggest that spontaneous GDM in the pregnant Lepr db/Ļ© mouse is triggered by overfeeding, and this effect results in obesity and insulin resistance in the livers of the adult offspring. The specific decrease in Akt phosphorylation in livers of adult offspring suggests that this may be a mechanism for reduced insulin-dependent physiologic events, such as suppression of hepatic glucose production, a defect associated with susceptibility to type II diabetes mellitus. Abbreviations GDM, gestational diabetes mellitus IGT, impaired glucose tolerance Lepr db/Ų , leptin receptor deficient WT, wild-type IUGR, intrauterine growth retardation IR-ā£, insulin receptor ā£ IRS-1, insulin receptor substrate-1 GLUT, glucose transporter PI 3-kinase, phosphotidylinositol-3-kinase Akt (c-PkB), related to A kinase, protein kinase B G-6-Pase, glucose-6-phosphatase HGP, hepatic glucose production Fetal growth and development are primarily determined by the fetal genome, however, the genetic regulation of fetal growth is influenced by different maternal factors, which can exert a stimulatory or an inhibitory effect. Epidemiologic studies have revealed strong statistical links between nutritional experiences during pregnancy and later development of diseases such as obesity and type II diabetes in adulthood (1, 2). Most convincing are the studies in Pima Indians demonstrating that, besides a genetic transmission of diabetes, the...