Diabetes during pregnancy has considerable adverse effects on the mother and her fetus or neonate. Mother’s hyperglycemia may induce hyper insulinemia and pancreatic Beta cells hyperplasia in fetus. Excess Insulin secretion in fetus blood may cause macrosomia, increase basal metabolism rate, increase oxygen consumption and even fetus hypoxemia. Fetal hypoxia may fallow by erythropoietin over production, red blood cell hyperplasia and increased hematocrit level. Polycythemia may enhance blood circulation and cause hyper bilirubinemia. On the other hand hyperglycemia may cause exaggerated production of oxygen radicals in mitocondrias and produce hydroperoxides which are prostacyclin inhibitors. Erythropoietin excess and polycythemia induce catecholamine release, hypertension and myocardial hypertrophy respectively. The last may be one of the etiology of still birth in poor control diabetic pregnancies. Rigorous glycemic control before and during pregnancy may decrease the prevalence of these complications.