Background: The definitions and approaches used to diagnose gestational diabetes (GD) are varied. The two-step approach recommended by the American College of Obstetricians and Gynecologists (ACOG) combines the sensitivity of a glucose challenge test (GCT) with the specificity of a 3-hour oral glucose tolerance test (OGTT). We investigated if minor modification of the two-step procedure can provide improved detection of GD by identifying a risk group of pregnant women with high risk of GD. Methods: We conducted a prospective cohort study of pregnant women enrolled early during pregnancy and followed till delivery. All participants underwent the ACOG-recommended two-step procedure for GD diagnosis. Based on GCT and OGTT results, the participants were divided into four risk groups (RG)s: GCT negative (RG0), GCT positive but OGTT normal (RG1), single abnormal value on OGTT or raised HbA1c (RG2) and diagnosed GD (RG3). Baseline evaluation included dietary history (24-hour recall) and physical activity. A series of multivariable logistic regression analyses were conducted to estimate the odds of maternal and fetal outcomes. Results: A total of 1,041 pregnant women were included in the study of who 16 (1.6%) were diagnosed as GD. Our two-step approach identified 48 (4.6%) women as GD while the RG2, RG1 and RG0 groups comprised 75 (7.2%), 218 (20.9%) and 700 (67.2%), respectively. Compared to RG0, the RG2 group showed a higher likelihood of antepartum complications [odds ratio and 95% confidence interval 2.38 (1.16-4.15)], any adverse outcome without [2.04 (1.17-3.55)] or with cesarean section [2.09 (1.21-3.61)], and primary cesarean section [1.68 (1.01-2.81)] after adjustment for potential confounders. The RG2 group was also significantly associated with pregnancy induced hypertension, meconium-stained amniotic fluid and premature rupture of membranes. Conclusions: In the study participants, we identified a subgroup (RG2) at high risk of GD with perinatal outcomes showing profile consistent with that of GD.