This investigation is a randomized controlled clinical trial to determine the effect of OAT bran on blood glucose profile in gestational diabetes Mellitus. Inclusion criteria consists of: Eligible participants were 20-40 years singleton pregnant women with <34 weeks gestation, whose GDM were detected by an endocrinologist based on one-step approach, as proposed by the IADPSG, that is, fasting blood glucose ≥ 92 mg/dl or one hour glucose after ingestion of 75 g glucose ≥180 mg/dl, or two hour glucose ≥ 153 mg/dl. Women with pre-gestational diabetes and chronic medical conditions including heart, kidney and gestational diseases or high blood pressure were excluded from the study. Other exclusion criteria included having celiac or allergic reactions to oat bran, lactation during the past three months, and unwillingness to follow the prescribed diet.This clinical trial was conducted on 90 women visiting the clinics that were randomly divided into two groups, control and intervention. Three modes treatment are (treatment with insulin, metformin, the treatment regimen). Patients treated with insulin and metformin after 2 weeks run-in which blood sugar is to achieve stability. All patients entering the study were randomly divided into two groups, control and intervention. Interventions in the control group will receive only diet based on ADA individuals in addition to diet control, 30 grams of Oat bran daily receive weather. At the beginning and end of the study, weight, glucose, glucose 2 hours after a meal, fructosamine and HbA1C is measured. According to the doctor if the patient is in need of special treatment the patient is excluded (but not including insulin)