Aim: To determine the incidence of gestational diabetes mellitus (GDM) and assess the fetal birth weight and occurrence of fetal macrosomia using 75gram oral glucose tolerance test (OGTT) World Health Organisation (WHO) criteria and 100gram OGTT Carpenter and Coustan criteria. Method: A comparative prospective study of pregnant women with risk factors for GDM. At 24 to 28 weeks of gestation, 400 pregnant women with risk factors for GDM were screened with 50gram glucose challenge test (GCT). All ‘screened positive’ women (i.e.1 hour plasma glucose level ≥ 7.8mmol/l) were subjected to have both 75gram and 100gram OGTT within 1 week apart. Diagnosis of GDM was made based on the result of either test, and pregnancy outcome observed.