Gestational diabetes mellitus (GDM) is the onset of impaired glucose or carbohydrate metabolism that is diagnosed during pregnancy. In the past GDM had a high maternal mortality rate. Approximately 30% of pregnant women died due to diabetic ketoacidosis, and the perinatal mortality rate was between 60% and 70%. Today, complications due to GDM have dramatically declined because of advances in research and successful management of blood glucose levels during pregnancy.

Impaired glucose metabolism is influenced by the hormones of pregnancy but may have been present before pregnancy. Gestational diabetes is diagnosed during the 24th to 28th week of pregnancy, and values generally return to normal after delivery. GDM is the most common medical complication in pregnancy and affects approximately 3-8% of all pregnancies in the United States. Any woman who has had GDM in a previous pregnancy has a 60-70% risk for developing it with subsequent pregnancies or to develop adult-onset diabetes in the future.

GDM carries certain risks to both the woman and her fetus. Those risks increase if the woman does not have adequate blood sugar control during the perinatal period. The American Diabetes Association recommends that all pregnant women be screened for GDM by gestational weeks 24-28 by using a 50-g glucose tolerance test. It is also recommended that women with GDM undergo reclassification of the disease 6 weeks postpartum.