The prevalence of preexisting diabetes in pregnancy is increasing largely because of an increase in type 2 diabetes. Outcomes of diabetic pregnancies for mother and newborn have improved greatly in recent decades from advances in understanding the disease process, improved education, and new treatment modalities delivered in a team approach. Nausea and vomiting from pregnancy and pregnancy-associated insulin resistance can make glycemic control a challenge. Care of women with preexisting diabetes demands careful monitoring in the preconception, prenatal, and peripartum periods.