Treatment of type 2 diabetes in pregnancy: Do we need to use metformin?

Maternal type 2 diabetes (T2D) is associated with an increased risk of several pregnancy complications and its prevalence is rising globally. Metformin, an oral medication that is first-line therapy for T2D outside of pregnancy, has the potential to improve glycemic control and reduce insulin requirements, without contributing to maternal hypoglycemia or weight gain. However, it crosses the placenta, and up until recently, very few clinical trials existed that studied its role in T2D pregnancies. Furthermore, concerns exist regarding potential effects of in utero metformin exposure on the offspring in the long-term. In this review we summarize available evidence to date on this topic, propose reasons for heterogeneity across studies, and discuss ongoing gaps in knowledge that will need to be addressed by future research.