The aim of the paper was to present data that enable us to determine whether treatment of hyperglycemia diagnosed during pregnancy, in the era of a steadily growing number of women with gestational diabetes mellitus (GDM) and an ongoing debate about new criteria and diagnostic strategies, is a valid option. GDM is the main metabolic disorder developing during pregnancy, complicating around 6% of all pregnancies. Mistreatment of hyperglycemia during pregnancy may cause several fetal complications, especially neonatal overgrowth (macrosomia or LGA). The risk of macrosomia is directly related to maternal hyperglycemia (twice as high as in the control group with glucose levels exceeding 130 mg/dl). Apart from maternal hyperglycemia and fetal hyperinsulinemia, insulin-like growth factors and selected adipocytokines produced by adipose tissue and placenta are among the factors contributing to the development of diabetic fetopathy, whose risk increases by 2-fold with glucose levels exceeding 130 mg/dl. The role of hyperglycemia as a factor inducing several perinatal complications was confirmed by the HAPO study, but it is not the sole reason of adverse effects. Also, maternal obesity, weight gain during pregnancy and maternal hyperlipidemia seem to be involved in the pathogenesis of feto-maternal complications. Changes in fetal growth, disturbances in the perinatal period, there just some of the negative consequences of maternal GDM. Disturbance of carbohydrate metabolism during pregnancy causes long-lasting consequences for both, the mother and the child, including increased risk of overt diabetes, metabolic syndrome and cardiovascular complications. Children born to GDM mothers are at a significant risk of psycho-motoric disability and a higher risk of schizophrenia. ACHOIS and MFMU studies have confirmed that even mild hyperglycemia, detected and treated in a timely manner, significantly improves maternal and fetal outcome. Various meta-analyses have revealed a positive effect of GDM treatment. To the best of our knowledge, no clinical study has revealed negative effects of such treatment, with the exception of an increased number of perinatal visits.