OBJECTIVE To discover the risk factors for developing hypoglycemia in newborns born to diabetic mothers and to characterize the rates of glucose concentrations in the first two days of life. METHODS Retrospective recordings of medical charts of 576 healthy term infants of diabetic mothers during an 18-month period. We determined the following pre-feeding glucose concentrations: 'normoglycemia' (> or =47 mg/dl = 2.6 mmol/l), 'mild hypoglycemia' (40-46 mg/dl = 2.2- 2.5 mmol/l), 'moderate hypoglycemia' (30-39 mg/dl = 1.7-2.1 mmol/l) and 'severe hypoglycemia' (<30 mg/dl = 1.7 mmol/l). RESULTS Glucose concentrations below 'normoglycemia' and 'severe hypoglycemia' were observed in 280 (48.6%) and 23 (4%) of the infants, respectively. The main risk factors for developing glucose concentrations below 'normoglycemia' in the first day of life were large size for gestational age and maternal insulin-dependent diabetes mellitus. 'Severe hypoglycemia' was more common among infants born to mothers who needed insulin (either type A2 or insulin-dependent diabetes mellitus). Infants born to mothers with insulin-dependent diabetes mellitus were less mature, heavier, large for their gestational age and exhibited more 'severe and moderate hypoglycemia' in the first day of life as compared to infants born to diabetes type A1 and A2 mothers. In addition, infants who were large for gestational age tended to have more 'moderate hypoglycemia' when born to diabetes type A1 mothers compared to small and appropriate-for-gestational-age infants. Thirty infants (5%) still had hypoglycemia on the second day of life. This subgroup of infants did not differ with regard to maternal-type diabetes. CONCLUSIONS Infants born to diabetic mothers tend to have a high rate of hypoglycemia on the first day of life when a relatively high cut-off point (> or =47 mg/dl = 2.6 mmol/l) is used. Infants born large for gestational age as well as those born to mothers with juvenile diabetes mellitus are at higher risk and should be closely monitored.