Gestational diabetes mellitus (GDM) is defined as carbohydrate intolerance that begins or is first recognized during pregnancy. 1 Although it is a well-known cause of pregnancy complications, a systematic review of its epidemiology has become more complex following the introduction of new World Health Organization (WHO)/International Association Diabetes in Pregnancy Study Group (IADPSG) international criteria that are for the first time based on the risk of adverse perinatal outcomes. 2 A further problem is the distinction of GDM from preexisting but undiagnosed diabetes, so that the degree of clinical surveillance may have a major impact on the estimated prevalence of GDM in a given population. This is especially true in high-risk populations in which the onset of type 2 diabetes mellitus (type 2 DM) occurs at an early age. 3 Further, investigators have used different screening programs and diagnostic criteria for GDM, making comparisons among studies difficult.