Gestational diabetes, also known as gestational diabetes mellitus or GDM, is diabetes that women develop during pregnancy. It occurs in about 135,000 cases, or 4 percent, of U.S. pregnancies annually. Some women with GDM will go on to develop type 2 diabetes later in life; it's been estimated that having GDM in pregnancy increases your type 2 risk by up to 50 percent. For this reason, regular diabetes screening is important for women with a history of GDM.