Pregnancy affects both the maternal and fetal metabolism and even in nondiabetic women exerts a diabetogenic effect. Among pregnant women, 2 to 17.8% develop gestational diabetes. Pregnancy can also occur in women with preexisting diabetes, that can predispose the fetus to many alterations in organogenesis, growth restriction and the mother to some diabetes-related complications like retinopathy and nephropathy or accelerate the course of these complications if they are already present. Women with gestational diabetes generally start their treatment with diet and lifestyle modification; when these changes fail in keeping an optimal glycemic control, then insulin therapy must be considered. Women with type 2 diabetes in use of oral hypoglycemic agents are advised to change to insulin therapy. Those with preexisting type 1 diabetes must start an intensive glycemic control, preferably before conception. All these procedures are performed aiming to keep glycemic levels normal or near-normal as possible to avoid the occurrence of adverse perinatal outcomes to the mother and to the fetus. The aim of this review is to reinforce the need to improve the knowledge on reproductive health of women with diabetes during gestation and to understand what are the reasons for them failing to attend for prepregnancy care programs, and to understand the underlying mechanisms of adverse fetal and maternal outcomes, which in turn may lead to strategies for its prevention.