Diabetes in pregnancy is unique because of the diversity of problems that can affect the embryo/fetus beginning with conception. Considerable effort has been devoted to understanding the basic developmental biology from observing young embryos in vitro or in vivo. Maternal glucose control has been identified as an important event. The preponderance of evidence indicates that rigid glucose control will minimize the incidence of anomalies incurred before 9 weeks of pregnancy. Later events are related to fetal hyperinsulinemia. These include fetal macrosomia, respiratory distress syndrome, neonatal hypoglycemia, neonatal hypocalcemia, and neonatal hypomagnesemia. Control of maternal metabolism can have a significant impact on each of the above. Finally, the long-term effects of maternal diabetes are as diverse as the pathogenetic events during pregnancy. Surprisingly, there is a significant transmission rate of 2% of type I diabetes if the mother has insulin-dependent diabetic mother, whereas the rate is 6% for the father. The Diabetes in Early Pregnancy Study showed that good maternal control was associated with normal neurodevelopmental outcome.