BACKGROUND/OBJECTIVES: The objective of this study was to examine the relationship between upper distribution levels of glucose values in the 75 -g oral glucose tolerance test (OGTT) and recommended diagnostic criteria for gestational diabetes mellitus (GDM) and adverse pregnancy outcomes. SUBJECTS/METHODS: The distribution of the OGTT 2-h values of 13 501 pregnant women, which were below the World Health Organization (WHO) threshold for overt diabetes mellitus (DM), and managed in one teaching hospital in China, was reviewed and related to maternal characteristics and pregnancy outcomes. RESULTS: For the entire group, the 90th and 95th percentile values of the OGTT 2-h glucose level, respectively, were close to the diagnostic cutoff values of the WHO and International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria. For adverse maternal outcomes, glucose level above the 90th percentile value was associated with increased hypertensive disorders, whereas no difference was seen with cutoff using the 95th percentile value. For perinatal outcomes, the 90th percentile was associated with increased neonatal intensive care unit admission and hypoglycemia, whereas the 95th percentile showed in addition association with phototherapy for jaundice and 5th-minute Apgar score < 7. Although no differences in the incidence of adverse pregnancy outcomes were found using the different cutoffs, the > 95th percentile cutoff value would have missed out 33.3-56.7% of the cases of adverse outcomes that would otherwise have been attributed to GDM. CONCLUSIONS: Further studies are warranted to clarify which diagnostic criterion is most appropriate universally to identify adverse pregnancy outcomes attributed to GDM, and which could be mitigated with treatment specific for GDM.