Women with preexisting diabetes are at increased risk of adverse pregnancy outcomes and birth defects. Women with gestational diabetes are at increased risk for adverse outcomes, including neonatal hypoglycemia, hyperbilirubinemia, macrosomia, increased risk of obesity and diabetes in the offspring later in life, and increased risk for other maternal comorbidities. Studies have shown that tight glycemic control before and during pregnancy can decrease the risk for adverse outcomes, congenital malformations, and maternal complications resulting from maternal preexisting diabetes. It is important to identify women with gestational diabetes and provide interconception care to minimize the risk of a future pregnancy complicated by type 2 diabetes. To reduce the risk of adverse consequences for both the woman and her baby, it is important to effectively manage diabetes before, during, and after pregnancy. Several professional organizations have developed guidelines in an effort to establish some consistency in the diagnosis and treatment of diabetes and to decrease the risk of adverse outcomes. The objectives of this paper are to (1) compare the guidelines for women with preexisting (types 1 and 2) and gestational diabetes available to healthcare providers in the United States, highlighting the similarities and differences among them, and (2) discuss how differences among the guidelines might affect efforts to address the challenges of controlling and preventing diabetes and resulting complications during pregnancy.