Diabetes mellitus is a chronic metabolic disease which is characterized with chronic hyperglycemia and disturbed metabolism of carbohydrates, proteins and fats. There are four types of diabetes mellitus depending on the etiology. The most common are type 1 and type 2 diabetes mellitus. Women with pregestational diabetes mellitus have high-risk pregnancies due to the possible development of maternal, fetal and neonatal complications. Poor metabolic control of glucose levels in pregnant women is associated with an increased risk of miscarriage, preeclampsia, birth of children with congenital malformations, stillbirths, asphyctic, premature and macrosomic children, and increased neonatal mortality. Good metabolic control during pregnancy significantly reduces the incidence of complications and approaches the level of incidence in the normal population of pregnant women. The optimal metabolic control of pregnant women is achieved with intensive insulin therapy, adequate nutrition, frequent glucose control and good antenatal care. Pregnant women with diabetes should be monitored and treated in regional centers for the treatment of diabetes in pregnancy. The supervision and care of such pregnancies involve a team of experts composed of obstetricians, diabetologists, neonatologists, dietitians, nurses and social workers.