ObjectivesThis study aimed to assess the prevalence of gestational diabetes mellitus (GDM) based on two sets of criteria, namely the old criteria suggested in 2009 by the American Diabetes Association and new criteria of the International Association of Diabetes in Pregnancy Study Group. We also evaluated the predictive power of the risk factors of GDM.MethodsPregnant women from three outpatient clinics in Tehran, Iran, participated in this cross-sectional observational study. During the first perinatal visit, demographic data, medical histories, weight, and height of mothers were recorded. The mother’s fasting glucose and glycosylated hemoglobin were measured. An oral glucose tolerance test was also performed. The prevalence of GDM, based on the two criteria, was estimated and its predictive factors were investigated.ResultsOf 1,117 pregnant women, 156 (15.6%) and 71 (7.1%) patients had GDM based on the new and old criteria, respectively. Multivariate analysis showed that older age at pregnancy (OR = 1.05; 95% CI: 1.006 - 1.107; P = 0.03), higher body mass index (OR = 1.2; 95% CI: 1.15 - 1.3; P < 0.001), family history of diabetes (OR = 1.97; 95% CI: 1.11 - 3.5; P = 0.02), and history of macrosomia (OR = 7.8; 95% CI: 1.96 - 30.9; P = 0.004) were independent predictive factors for GDM.ConclusionsUsing the new criteria, the prevalence of GDM increases by 2.2 folds compared to the old criteria. Several factors can independently predict the occurrence of GDM.