Objective: To examine if addition of metformin to insulin is an effective alternative to insulin alone, to lower insulin dose, hospital stay, maternal and neonatal complications in pregnant women at third trimester with uncontrolled type I Diabetes Mellitus, particularly in a resource-poor setting.  Material and method: Our randomized controlled trial included 80 patients, who were distributed into two equal groups; group A treated with metformin and insulin and group B treated with insulin alone, in Beni-suef and Cairo University hospitals. Results: We found that metformin and insulin group (Group A) showed significant outcomes regarding shortened hospital stay, lower insulin dose and lower maternal weight gain during pregnancy (p values: 0.04, 0.02 and 0.03 respectively). Most of maternal and neonatal complications were non-significantly lower in group A. Conclusion: Oral metformin therapy is an effective and safe additional treatment option for diabetic women with type I diabetes during pregnancy to lower insulin requirements, hospital stay and most maternal and fetal complications, especially in settings with limited economic resources.