Data from previous studies show that the incidence of GDM in Iran is between 4.8-7.4% (7, 9, 10). We have estimated incidence of GDM in pregnant women at low risk for GDM according to ADA recommendation (5). Our results showed if we did not screen low risk pregnant women for GDM we would have missed one woman with GDM. In agreement with other studies (11-14), this group included few women with a low risk of GDM, resulting in a very low incidence. This would provide evidence for an acceptable performance of the selective screening, because it would miss no more than 2.1% of GDM in a low risk population. In the present population, about 97.2% were at medium/high risk for GDM, showing an acceptable indication for screening.