Gestational diabetes mellitus (GDM) is defined as diabetes that is first recognized during pregnancy, and occurs in about 3 % - 5 % of all pregnancies. GDM is a heterogeneous metabolic disorder that may be associated with an increased perinatal morbidity and perinatal mortality rates. When not diagnosed or when treated incorrectly, GDM is associated with adverse maternal and fetal outcomes. GDM is typically asymptomatic, and the diagnosis must be sought actively. WHO suggests all women be screened between 24th and 28th gestational week. The aim of the therapy is to prevent complications of GDM. The most devasting complications are macrosomia and stillbirth. Macrosomia may predispose infants to childhood obesity and probably to adult obesity. Treatment as well as the aim of the treatment remain the same as in diabetic women during pregnancy. 10 – 30 % of GDM require insulin treatment Gestational diabetes resolves after delivery, but may reccur in subsequent pregnancies, and the life time risk of developing type 2 diabetes is 30 %.