1. A screening test is done at 24 to 28 weeks of gestation by measuring blood glucose one hour after a non-fasting patient consumes a 50-gram dose of glucose. A result greater than 140 mg/dL is usually used as the cutoff, although a lower cutoff of 130 mg/dL may also be used. Those with a result greater than the cutoff undergo diagnostic testing.
2. The diagnostic test is the three-hour oral glucose tolerance test (OGTT). This test requires the collection of a fasting blood sample followed by consumption of a 100-gram dose of glucose with additional blood samples obtained every hour for four hours. The test is considered positive, and GDM confi rmed, if two or more of the four glucose test results are above designated cutoffs. There are two sets of cutoffs currently used: those of the National Diabetes Data Group or the Carpenter-Coustan cutoffs.