Background: Overweight and high parity are two of the many risk factors for gestational diabetes mellitus that affect women in Saudi Arabia. In order to minimize complications for both the mother and the fetus, care of gestational diabetes mellitus should involve keeping the patient's plasma glucose levels within normal ranges and avoiding significant weight gain. Insulin was the first line of therapy for diabetes during pregnancy. Metformin safety was approved recently, and it was administered more frequently to pregnant diabetes patients when insulin cannot be provided. Method: We conducted a thorough search of the Cochrane database, Embase, and PubMed (from 2015 to 2022). We looked for randomized controlled trials that contrasted metformin with insulin. Results: In the systematic review, we considered 6 studies with 996 patients overall. Five studies excluded mothers with pre-gestational diabetes, and one research did not state whether pre-gestational diabetes was present. In these six RCTs, 498 participants got insulin therapy, and 498 patients got metformin treatment. In Ashoush et al., (2016) study, 22% of the metformin group needed insulin throughout the follow-up period. In most of the included studies the two groups differed statistically significantly regarding gestational age at birth. Conclusion:our study shows that, when compared to insulin treatment, metformin can provide some benefits and acceptable glycemic control without increasing the risk of certain outcomes for mothers and neonates. More researches were needed in Middle East and especially in Saudi Arabia.