The glucose challenge test: a screening test for gestational diabetes mellitus

The 50g glucose challenge test (GCT) was evaluated as a method to screen for gestational diabetes in 540 low-risk pregnant women to establish its sensitivity and specificity, as well as to establish a relevant threshold plasma glucose value above which a diagnostic 75g oral glucose tolerance test (OGTT) would be indicated. If a threshold of 140 mg/dl is used, the diagnostic yield would be 28.5%. At a threshold of 130 mg/dl, the diagnostic yield fell to 25.4%; the sensitivity rose to 87.7% and the specificity declined to 67.1%. There was progressive increase in diagnostic sensitivity when the GCT was performed after 24 weeks without significant decrease in specificity. In low-risk populations, a 50g GCT should be performed between 24-28 weeks gestation.