Objective To determine the normal response to a 75 g glucose challenge in the context of an oral glucose tolerance test in the third trimester of pregnancy. Design Prospective observational study. Setting Antenatal clinic, Kandang Kerbau Hospital, Singapore. Subjects Sixty‐four normal pregnant women with a low risk for diabetes. Interventions Glucose (75 g) challenge following an overnight fast after 28 weeks of gestation. Main outcome measure Venous plasma glucose levels taken before and 2 h after the glucose challenge. Results Upper limits of normality were found to be fasting glucose 4·9 mmol/l and 2 h glucose 9·2 mmol/l. Conclusion The WHO (1980) criteria should not be used in pregnancy.