In this large, multinational study, glucose levels that were increased during pregnancy but were below levels diagnostic of diabetes were significantly associated with increased risks of birth weight above the 90th percentile and C-peptide levels above the 90th percentile, as well as with other adverse pregnancy outcomes. These results indicate the need to reconsider current thresholds for diagnosing and treating hyperglycemia during pregnancy. Glucose levels that were increased during pregnancy but were below levels diagnostic of diabetes were significantly associated with increased risks of birth weight above the 90th percentile and C-peptide levels above the 90th percentile, as well as with other adverse pregnancy outcomes. Gestational diabetes mellitus, defined as “glucose intolerance with onset or first recognition during pregnancy,” 1 , 2 has been the subject of considerable controversy. Criteria for the diagnosis were initially established more than 40 years ago 3 and, with minor modifications, remain in use today. These criteria are not designed to identify pregnant women who are at increased risk for adverse perinatal outcomes but rather women who are at high risk for the development of diabetes after pregnancy, 3 , 4 or they are the criteria used for the general population. 5 Overt diabetes mellitus during pregnancy is associated with significantly increased risks of adverse perinatal . . .