Threshold value of glucose screening tests in pregnancy: could it be standardized for every population?

We aimed to determine a threshold value that perfectly demarcates women at high risk for gestational diabetes mellitus (GDM) in the Turkish population. One thousand gravid women of 24 to 32 weeks of gestation were given 50 g, 1-hour glucose screening tests. A 100 g, 3-hour glucose tolerance test (GTT) was performed on all patients whose screening test plasma glucose value was 130 mg/dL or greater. The sensitivity and specificity of each screening test value was found, and the GDM rate of each value was calculated. Three-hundred-and-five patients were identified for GTT and 66 were shown to have GDM with two or more abnormal values in GTT. The incidence of GDM was found to be 6.6%. The maximum specificity and sensitivity were met at 140 mg/dL. However, this value underestimated 12% of patients with GDM, and the lowest value for a positive GTT appeared to be 134 mg/dL. We recommend a 135 mg/dL threshold for GTT since this threshold accurately diagnoses almost all women with GDM while eliminating unnecessary GTT.