Introduction: Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance 
with onset or first recognition during pregnancy. Aim of the work: The aim of this study is to 
compare the efficacy of metformin with that of insulin in treatment of gestational diabetes mellitus.
Patients and Methods: This two armed clinical trial was conducted prospectively on 100 pregnant 
women on regular antenatal care in the Diabetic Clinic of Minia Maternity Hospital during the period 
from January 2016 to September 2017. Results: This study included 95 pregnant women having 
GDM, 47 of them were treated with metformin, and the remaining number (48) were treated with 
insulin. Conclusion: Approximately 80% of women with GDM could be successfully and safely 
treated with metformin when diet therapy and exercise fail to reduce blood glucose values sufficiently.