The ongoing epidemics of obesity and diabetes have led to higher incidence of gestational diabetes mellitus and pregestational diabetes. GDM is diabetes diagnosed in the second or third trimester of pregnancy that is not clearly overt diabetes. Therefore, women in whom diabetes is detected in the first trimester would be classified as having type 2 diabetes. Women with GDM should be screened for persistent diabetes or prediabetes at 6∼12 weeks postpartum. All women of childbearing age with diabetes should be counseled about the importance of strict glycemic control prior to conception. During pregnancy, treatment with angiotensin-converting enzyme inhibitors and angiotensin receptor blockers is contraindicated because their ability to cause fetal damage. Women with diabetes of any kind should be supported in attempts to breastfeed, as it is related to long-term metabolic benefit to both mother and child.