Gestational diabetes mellitus (GDM) is defined as carbohydrate intolerance with onset or first recognition during pregnancy. If insulin resistance and hyperglycemia are recognized before pregnancy, the term pregestational diabetes (PGD) is used. In the last years, much has been invested to uniformly define worldwide the diagnostic criteria and the management of gestational diabetes. A general screening in a low risk population should be implemented into routine prenatal care. Similarly, pregnant women at high risk for metabolic disorders should be screened in the early pregnancy.