This is an observational prospective cohort study conducted in our Department of Obstetrics. All women are tested for HbA1c at the first antenatal visit during the first trimester. First trimester was defined as up to 12 6/7 weeks of gestation. Between 24 and 28 weeks of gestation the women are screened, as internationally proposed, by a "one-step" standardized 75g oral glucose tolerance test (oGTT). Venous blood samples were collected at 0, 1, and 2h after the glucose load. Women with pre-existing diabetes mellitus or a first trimester HbA1c ≥6.5% are excluded from the study und medical care for pregestational diabetes is provided.