Gestational diabetes mellitus (GDM) was originally defined using statistics. It is appropriate to examine the current state of screening for gestational diabetes using a similar approach. This article reviews data supporting current recommendations for universal screening of pregnant women for GDM at 24-28 weeks using the 50-g 1-h oral glucose challenge. The advantages and disadvantages of several thresholds for abnormality are discussed, as are possible alternatives to the 50-g 1-h oral glucose challenge. Finally, recent improvements in the precision of portable blood glucose meters are reviewed, and recommendations for their use are advanced.