A comparison between a 75-g and 100-g oral glucose tolerance test in pregnant women.

OBJECTIVES: To test the validity of a 75-g, 2-h oral glucose tolerance test (OGTT) for diagnosing gestational diabetes mellitus (GDM) using the criteria and reference values suggested by the American Diabetes Association for the 100-g, 3-h OGTT. METHODS: The results of a 75-g, 2-h OGTT were compared with those of a 100-g, 3-h OGTT in 42 pregnant women. The women's mean+/-S.D. age and gestational age were 33.6+/-5.4 years and 28.2+/-4.2 weeks, respectively. Each subject was randomly scheduled within 1 week for both the 75-g and 100-g OGTTs. RESULTS: The mean plasma glucose concentrations at 1, 2, and 3 h during the 100-g OGTT were significantly higher than those during the 75-g OGTT. Using the Carpenter and Coustan criteria, the prevalence of GDM was 21.4% when using the 100-g, 3-h OGTT, whereas it was found to be at only 7.1% when using the 75-g, 2-h OGTT. CONCLUSIONS: Plasma glucose responses during the 75-g OGTT were found to be lower than those during the 100-g OGTT. When using the same diagnostic criteria, the prevalence of GDM was also found lower using the 75-g glucose load. It would therefore not be appropriate to use the 75-g OGTT for diagnosing GDM using the criteria and reference values of the 100-g OGTT. To give a comparable prevalence of GDM, the threshold of abnormal plasma glucose levels of the 75-g OGTT would need to be lower than that of the 100-g OGTT.