Introduction
Glycaemic control in women with gestational diabetes mellitus (GDM) has typically been achieved with diet, exercise and insulin therapy. Controversy exists in the literature about a potential role for metformin.

Methods
A literature review was completed aiming to compare the glycaemic control, maternal and fetal out comes of metformin therapy with insulin. Searches were completed on databases, including Medline, PubMed and ScienceDirect. Seven randomised control trials (RCTs) fit the inclusion criteria, with a total sample size of 1514 women.

Results
The majority of studies found no difference in glycaemic control between metformin and insulin groups. When comparing maternal outcomes, those receiving metformin therapy recorded less maternal weight gain in four studies. A number of studies reported lower rates of neonatal hypoglycaemia, and one reported higher rates of preterm birth in the metformin group. There were no other differences in the recorded maternal and fetal outcomes.

Discussion
The Jadad score for assessing risk of bias for most included studies was either 3 or 4. The criteria for diagnosis of GDM, maternal and neonatal complications varied between studies. Only one study has published follow‐up data, and most are single‐centre trials with relatively small sample sizes.

Conclusion
Though there is a growing body of evidence to suggest a role for metformin in GDM management, further large‐scale, multicentre RCTs are needed before guidelines can be altered.