Objective: To determine the prevalence of gestational diabetes mellitus (GDM) and gestational impaired glucose tolerance (GIGT) using National Diabetes Data Group (NDDG), and Carpenter and Coustan (CC) criteria. Method: Retrospective study of the prevalence of GDM and GIGT in 21 531 pregnant women screened for GDM between 2005 and 2007 using NDDG and CC criteria. Linear trends in prevalence of GDM and GIGT by age were calculated using logistic regression. Results: Mean prevalence rates for GDM were 3.17% (95% CI, 3.05-3.29; n = 683) and 4.48% (95% CI, 4.36-4.6; n = 964) according to NDDG and CC criteria, respectively. Mean prevalence rates for GIGT were 1.97% (95% CI, 1.85-2.09; n = 426) and 2.46% (95% CI, 2.34-2.58; n = 529) according to NDDG and CC criteria, respectively. Prevalence of GDM and GIGT increased with increasing age with both criteria (P < 0.001). The prevalence of GDM increased by 41.1% and GIGT increased by 24.2% using the CC criteria compared with the NDDG criteria. Conclusion: The prevalence of GDM and GIGT was higher when CC criteria were used compared with NDDG criteria, particularly in younger age groups. The prevalence of both GIGT and GDM increased with increasing age with both criteria. © 2009 International Federation of Gynecology and Obstetrics.