Background: Recently, the American Diabetes Association (ADA) concluded that pregnant women with low risk factors for gestational diabetes need not to be tested. The aims of this study was to determine the prevalence of gestational diabetes in a Spanish low risk pregnant women population, to analyze the criteria that define low risk pregnancies for gestational diabetes, and to compare the differences in morbidity between pregnant women with and without gestational diabetes., Design and Methods: Cohort study of 2,262 gestations (2,085 Caucasians) during a period of 7 years in a reference hospital., Results: The gestational diabetes prevalence was 15%. Two-hundred and seventy-four (12.1%) women were considered as a low risk group for gestational diabetes. Among these, 13 (4.7%) presented gestational diabetes in comparison with 16.6% in the remaining women (p = 0.0001). Gestational diabetes in the low risk pregnant women constituted the 3.8% of all gestational diabetes. We did not find differences in gestational outcomes or fetal antropometry between the groups. The relative risk of macrosomia in the low risk pregnant was 0.9% (95% confidence interval for the mean: 0.86-0.94)., Conclusions: In spite of their capacity of identifying current complications, 4% of gestational diabetes would not have been diagnosed with the new ADA criteria. The misdiagnosis will prevent in this small group of women the adoption of preventive measures for subsequent pregnancies and for diabetes in later life.