We examined antepartum clinical characteristics along with measures of glucose tolerance, insulin sensitivity, pancreatic -cell function, and body composition in Latino women with gestational diabetes mellitus (GDM) for their ability to predict type 2 diabetes or impaired glucose tolerance (IGT) within 6 months after delivery. A total of 122 islet cell antibody-negative women under- went oral and intravenous glucose tolerance tests ( O G T T; IVGTT), hyperinsulinemic-euglycemic clamps, and measurement of body fat between 29 and 36 weeks' gestation and returned between 1 and 6 months post- partum for a 75-g OGTT. Logistic regression analysis was used to examine the relationship between antepar- tum variables and glucose tolerance status postpartum. At postpartum testing, 40% of the cohort had normal glu- cose tolerance, 50% had IGT, and 10% had diabetes by American Diabetes Association criteria. Independent antepartum predictors of postpartum diabetes were the 30-min incremental insulin:glucose ratio during a 75-g OGTT (P = 0.0002) and the total area under the diag- nostic 100-g glucose tolerance curve (P = 0.003). Inde- pendent predictors of postpartum IGT were a low first- phase IVGTT insulin response (P = 0.0001), a diagnosis of GDM before 22 weeks' gestation (P = 0.003), and weight gain between prepregnancy and the postpartum examination (P = 0.03). All subjects had low insulin sen- sitivity during late pregnancy, but neither glucose clamp nor minimal model measures of insulin sensitivity in the 3rd trimester were associated with the risk of IGT or dia- betes within 6 months' postpartum. These results high- light the importance of pancreatic -cell dysfunction, detectable under conditions of marked insulin resis- tance in late pregnancy, to predict abnormalities of glu- cose tolerance soon after delivery in pregnancies com- plicated by GDM. Moreover, the association of postpar- tum IGT with weight gain and an early gestational age at diagnosis of GDM suggests a role for chronic insulin resistance in mediating hyperglycemia outside the 3rd trimester in women with such a -cell defect. Diabetes 47:1302-1310, 1998