Metformin is a common treatment for women who have insulin resistance manifesting as type 2 diabetes or polycystic ovarian syndrome (PCOS). With an increasing number of these patients conceiving, it is expected that the use of metformin in and around the time of pregnancy will increase. This article reassesses the mechanisms, safety, and clinical experience of metformin use in obstetrics and gynecology. Metformin is an attractive therapeutic option because administration is simple, hypoglycemia rare, and weight loss promoted. There is a large volume of research supporting the use of metformin treatment in diabetes mellitus, androgenization, anovulation, infertility, and recurrent miscarriage. Although metformin is known to cross the placenta, there is, as yet, no evidence of teratogenicity. Metformin has an array of complex actions, accounting for the varied clinical roles, many of which are still to be fully evaluated. Much research is still needed.
Target Audience: Obstetricians & Gynecologists, Family Physicians
Learning Objectives: After completion of this article, the reader should be able to explain the pharmacokinetics of metformin, to describe the mechanisms of action of metformin, to list the potential applications of metformin use, and to outline the potential adverse effects of metformin.
There is a clinical impression that metformin use during and around the time of pregnancy is increasing. A survey by the Australasian Society for Diabetes in Pregnancy found that 25% to 50% of members would consider oral hypoglycemic agents in this setting (1). These Australasian clinicians favored metformin over glyburide or glibenclamide as alternatives to or additional treatment with insulin (1). This is despite arguably “higher-grade evidence” for the safety of glyburide than metformin (2, 3).
Given the clinical impression of increasing metformin use in pregnancy, a Medline search for English language papers using the terms “metformin” and “pregnancy” published between 1971 and December 2002 was conducted. Sixty publications were obtained, supplemented with articles from the reference lists of these 60 publications and papers in the authors’ personal libraries. Readers are also advised to consult the product information before prescribing.