Criteria for screening tests for gestational diabetes.

A 50 gm, 1-hour glucose screening test was given to 381 gravid women 25 years of age or older. All women with plasma glucose values greater than or equal to 130 mg/dl (119 mg/dl, whole blood) were given a 100 gm, 3-hour glucose tolerance test to diagnose gestational glucose intolerance using O'Sullivan's diagnostic criteria. On the basis of the distribution of screening test values, three diagnostic zones could be identified: a zone below 135 mg/dl plasma glucose, with less than 1% probability of diabetes; a zone above 182 mg/dl plasma glucose, with more than 95% probability of diabetes; and a central zone of uncertainty (135 to 182 mg/dl, plasma glucose), where further testing is required. These test results suggest that thresholds for further testing be lowered from 143 to 135 mg/dl of plasma glucose.