Diabetes mellitus is classified as a type 1 diabetes mellitus which occurs when the body fails to produce insulin. In type 2 diabetes mellitus, insulin is produced either in insufficient quantities or the cells are insulin resistant. The gestational diabetes is diagnosed for the first time in pregnancy. According to population surveys, the incidence of gestational diabetes is 2 to 6% of pregnant women and varies extensively across ethnic groups. The strongest risk factor is age. Diabetes mellitus is caused by absolute or relative lack of insulin or by its inefficacy. Diabetes in pregnancy can cause many problems for both mother and a child. Pregnant women with gestational diabetes have an increased risk of spontaneous miscarriage, preeclampsia, childbirth with congenital malformations and macrosomic babies. Fetal macrosomia is defined as an increase in body mass above 4000 g on the due date, or when the baby is greater than 90th percentile for its age. Intrauterine fetal growth is the result of the action of the gene potential and the growth support which the fetus receives over the mother's placenta. There is symmetric and asymmetric fetal growth. Most common complications that can affect mother are infections, preeclampsia, diabetic nephropathy and retinopathy. Fetal complications are usually anomalies of development, hypoxia, hypoglycemia, respiratory distress symptom, etc. OGTT (a two-hour, 75-gram oral glucose tolerance test) is caused as a criteria for diagnosis of GDM. Treatment is mainly carried out by basic measures and pills, and insulin is given only when the results are not satisfying. It is only administered parenterally, intramuscularly or intravenously. Midwife, as a part of education and the treatment of gestational diabetes, is obliged to inform about possible complications and risks