Tehran University of Medical Sciences Journal of Family and Reproductive Health 1735-8949 4 4 2010 12 15 165 168 Shirin Niroomanesh Department of Obstetrics and Gynecology, Mirza Koochackkhan Women's Hospital, Tehran University of Medical Sciences, Tehran, Iran Masoumeh Dadashaliha Department of Obstetrics and Gynecology, Mirza Koochackkhan Women's Hospital, Tehran University of Medical Sciences, Tehran, Iran Farahnaz Ahmadi Department of Obstetrics and Gynecology, Mirza Koochackkhan Women's Hospital, Tehran University of Medical Sciences, Tehran, Iran Fatemeh Rahimi Sherbaf Department of Obstetrics and Gynecology, Mirza Koochackkhan Women's Hospital, Tehran University of Medical Sciences, Tehran, Iran Forough Forghani Department of Obstetrics and Gynecology, Mirza Koochackkhan Women's Hospital, Tehran University of Medical Sciences, Tehran, Iran 2015 10 04 Objective: This study evaluated the efficacy and safety of metformin on prevention of gestational diabetes mellitus in women with high risk of GDM. Materials and methods: Total number of 189 pregnant women aged between 25 to 35, and 10 to 14 weeks pregnancy,admitted to  Mirza Koochakkhan Hospital, Tehran in January 2008 - January 2009 entered to this randomized controlled clinical trial. The women had one of the three risk factors; history of GDM, family history of diabetes, or BMI ≥ 30 kg/m2, with normal results in the glucose challenge test (GCT) or the glucose tolerance test (GTT). Subjects were randomly split to two groups; 63 women (group A) who received metformin (500 mg, twice a day) and 126 women (group B) did not use metformin. Incidence  of gestational diabetes was compared between two groups. Results: The incidence  of gestational diabetes was significantly different between two groups (%1.4 in group A, %15.4 in group B) (p<0.001). The study also showed that the insulin requirement was significantly different between two groups after developing GDM (group A %3.6, group B %9.5, p=0.001). Conclusion: Using Metformin can effectively reduce the incidence of GDM in pregnant women at risk. https://jfrh.tums.ac.ir/index.php/jfrh/article/view/109 https://jfrh.tums.ac.ir/index.php/jfrh/article/download/109/109