['Gestational diabetes mellitus (GDM), defined by two abnormal glucose values on a 3-h oral glucose tolerance test (OGTT), is associated with insulin resistance and a low serum concentration of adiponectin. The metabolic implications of impaired glucose tolerance (IGT) of pregnancy (i.e., a single abnormal value on an OGTT), however, are not well established. We sought to evaluate the metabolic phenotype of pregnant women with IGT in relation to the timing of their isolated hyperglycemia.', 'A cross-sectional study was performed in pregnant women undergoing a 3-h, 100-g OGTT. The OGTT stratified participants into four groups: 1) GDM (n = 48), 2) 1-h IGT (single elevated value at 1 h) (n = 15), 3) 2-h/3-h IGT (single elevated value at either 2 or 3 h) (n = 23), and 4) normal glucose tolerance (NGT) (n = 93). Insulin sensitivity was measured by the validated insulin sensitivity index (IS(OGTT)) of Matsuda and DeFronzo.', 'Measures of severity of glycemia (fasting glucose, area under the glucose curve from the OGTT, and glucose challenge test result) were highest in the GDM group, followed by the 1-h IGT, 2-h/3-h IGT, and NGT groups, respectively (each trend P < 0.0001). Consistent with this finding, IS(OGTT) was highest in the NGT group (5.1), followed by the 2-h/3-h IGT (4.6), 1-h IGT (3.8), and GDM (3.2) groups (trend P < 0.0001). Furthermore, on multiple linear regression analysis of IS(OGTT), both GDM and 1-h IGT were independently associated with reduced insulin sensitivity (whereas 2-h/3-h IGT was not). Mean adjusted adiponectin was highest in the NGT group (15.7 microg/ml), followed by the 2-h/3-h IGT (15.6 microg/ml), 1-h IGT (13.7 microg/ml), and GDM (12.0 microg/ml) groups (trend P = 0.0024).'] Is impaired glucose tolerance of pregnancy a heterogeneous metabolic disorder as defined by the glycemic response to the oral glucose tolerance test?