Metabolic characteristics of physiological and diabetic pregnancies are discussed. The basic factor of these changes is the increasing insulin resistance throughout pregnancy, which in case of diabetes may result in hyperglycemia with undesirable clinical consequences and complications for both the mother and the fetus. Prevention of these complications by maintaining physiological metabolic state of diabetic pregnant women is possible, which is similar to that of healthy women. The aim of treatment of pregnant diabetics is to achieve normoglycemic state during the whole gestation that is possible by early diagnosis in case of gestational diabetes and by adequate preconception care in case of pregestational diabetes. To obtain desirable glycemic conditions insulin treatment is necessary in most of the cases together with adequate, quantitative nutrition therapy, while oral antidiabetic drugs during pregnancy and lactation are to be avoided. For adequate care of the cases with diabetes and pregnancy interdisciplinary diabetes centers with well-trained experts are required.