Fetal glucose exposure and consequent fetal insulin secretion is normally tightly regulated by glucose delivery from the mother during pregnancy. Maternal hyperglycaemia and gestational diabetes (GDM) are known to be detrimental to offspring, although defining the criteria for diagnosis of GDM is controversial. Recent data suggest that the risk of poor fetal outcome appears to be a continuous variable across the range of glucose control, and that the level of maternal blood glucose for a diagnosis of gestational diabetes needs to be reviewed. After birth, rapid adaptation is necessary for infants to be able to maintain independent glucose homeostasis. This adaptation is compromised in infants who are small for gestational age (SGA), premature, or large for gestational age (LGA). Interestingly, the infants who are born at the extremes of birth weight are also at increased risk of impaired glucose tolerance and diabetes in later life.