Gestational Diabetes Mellitus (GDM) is a growing epidemiological problem, and it is currently the most common metabolic disorder in pregnancy, as it affects approximately 2-6% of all pregnant women. In 2014, the Polish Diabetic Association introduced significant changes in the diagnosis of hyperglycemia as first diagnosed in pregnancy, based on the recommendations of the IADPSG of 2010 and WHO of 2013. There are now two categories: diabetes in pregnancy, and GDM. These involve different degrees of severity of metabolic complications for the mother and the growing fetus. Establishing a new diagnostic criterion is significant because of the negative impact of hyperglycemia on the fetus (especially in the first trimester), the increased prevalence of malformations or the possibility of spontaneous abortions in early pregnancy.