While the routine approach for the diagnosis of gestational diabetes is 50-g glucose tolerance test and 100-g OGTT in cases of a positive screen, a new approach was brought to agenda after it was found in the study of Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study that there is a linear relationship between blood glucose levels and gestational outcomes, and this was found to be closely associated with each value increase. It was shown that the approach of establishing diagnosis based on a single value at once with 75-g OGTT which is recently common in clinical practice helps 18% of pregnant population to get diagnosed, and the diet and exercise following the diagnosis improved gestational outcomes and affected gestational outcomes even in obese cases without gestational diabetes. Pregestational obesity having effect on gestational outcomes even though there is no diagnosis of gestational diabetes and finding that keeping weight gain during pregnancy under control is improving gestational outcomes reveal the importance of this matter. While 75-g OGTT procedure based on single value increases the number of cases who are established the diagnosis of gestational diabetes compared to the two-step screening and diagnosis test, diet-exercise practice in cases with such diagnosis is a condition which keeps weight gain during pregnancy under control and also has a positive impact on gestational outcomes. Glycemia being above the desired range with 1–2 weeks of follow-up of the blood glucose will require medical treatment. This is an expected and desired target. Therefore, applying 75-g OGTT based on single value has become the new clinical practice and it is recommended. This clinical practice guideline was prepared by the Diabetes and Pregnancy Study Group of Turkish Perinatology Society.