Pregnancies complicated with diabetes mellitus, either previously diagnosed, or appearing during pregnancy, gestational diabetes , present an increased maternofetal risk. An additional risk of fetal malformations exists when diabetes is present before the beginning of pregnancy. Hyperglycemia plays a role in the occurrence of these complications but other factors, more or less identified, could also be implicated. Pregnancy may favor the occurrence or aggravation of diabetic retinopathy and/or nephropathy in patients with pre-existing diabetes. The pathophysiology of gestational diabetes includes insulin resistance and decreased insulin secretion, suggesting some commune aspects with type 2 diabetes. There is no international consensus about screening for gestational diabetes nor for diagnostic criteria. For gestational diabetes as in cases of pre-existing diabetes, treatment principles relay on dietetics and insulin. The improvement in medical care of pregnancies complicated by diabetes includes improvement in scientific knowledge and a specialized medical care of these patients.