How reliable is the fifty-gram, one-hour glucose screening test?

The Second International Workshop-Conference on Gestational Diabetes recommended screening all pregnant women with a 1-hour 50 gm oral glucose screening test, given without regard to time of day or time elapsed from the last meal. This study was designed to evaluate the reproducibility of that test, given under those clinical conditions. Thirty women with gestational diabetes and 80 control volunteers between 24 and 28 weeks' gestation were tested at the same time of day on two successive days. Of the 30 women with diabetes, three (10%) had glucose screening test results below the 135 mg/dl threshold on both days and 10 (33%) had results that straddled the threshold on successive days. Test results of 11 control women also straddled the threshold. Among these 21 women with results that straddled the threshold, there was no difference in mean glucose screening test results in diabetic women compared with nondiabetic ones. We conclude that, as currently recommended, the 1-hour glucose screening test is moderately reproducible. Reliance should not be placed on a single normal test result, particularly among patients with risk factors.