Weight gain during pregnancy is related to pregnancy outcomes that include preterm delivery, fetal macrosomia, and intrauterine growth restriction. The former two are common in women with diabetes; the latter one has become rare with better care and lower incidence of vascular complications in these women. 1 , 2 Optimal weight gain differs according to the maternal body mass index (BMI) and is lower in women with a high BMI. Weight loss during pregnancy is usually associated with an impaired outcome. In this chapter, optimal weight gain during pregnancy in women with diabetes is discussed.