Gestational Diabetes Mellitus (GDM) is one of the most frequent complications of pregnancy and is characterized by a carbohydrate intolerance which is diagnosed with the oral glucose tolerance test. The prevalence of GDM in our population is about 12%, but risk factors like a previous GDM, ethnicity, a parent with diabetes mellitus type 2 and maternal overweight may increase its occurrence. Complications of GDM are a pre-term birth (before 37 wk gestation), macrosomia (birth weight ≥4 kg) and gestational hypertension. Actually, GDM is principally treated with diet and, if it is necessary, with insulin; but the challenge is the prevention of GDM. Among the measures used, changes in life-style (diet+exercise) failed to prevent GDM whereas metformin showed conflicting results. A promising supplement is myo-inositol (MI) which was given from first trimester until delivery to women at risk for GDM reporting a significant decrease in GDM occurrence by more than 60% comparing to the placebo group. Recently, a secondary analysis from 3 randomized controlled trials demonstrated that MI may also significantly reduce some of GDM complications such as pre-term birth and macrosomia with a favorable impact on mother and fetus well being.