What is the role of metformin for the management of gestational diabetes mellitus (GDM)?

Updated: Apr 29, 2020
  • Author: Thomas R Moore, MD; Chief Editor: George T Griffing, MD  more...
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Metformin is a biguanide, which functions mainly by decreasing hepatic glucose output. Metformin crosses the placenta, and umbilical cord levels have been shown to be even higher than maternal levels. [90]

An initial retrospective study comparing glyburide, metformin, and insulin in pregnancy raised concern, because of increased rates of preeclampsia and perinatal mortality when metformin was used in the third trimester. [91] It should be noted that in this study the patients on metformin had a higher body mass index and were older than the patients on glyburide or insulin. Since this initial study, however, several other prospective and retrospective studies involving over 300 pregnant patients have not confirmed the increased rates of preeclampsia or perinatal mortality. [92, 93, 94, 95, 96] These subsequent studies have demonstrated similar efficacy, safety, and maternal and fetal outcomes with metformin.

Moore et al compared the effect of metformin and glyburide in women with gestational diabetes who did not achieve glycemic control with diet. Between the 2 groups, patients who achieved glycemic control did not differ with regard to mean fasting and 2-hour postprandial blood glucose level. However, the percentage of women who did not achieve glycemic control and required insulin was 2.1 times higher with metformin (34.7%) than with glyburide (16.2%). [8]

According to results from the PregMet 2 study, which involved pregnant women with PCOS from centers in Norway, Sweden, and Iceland, metformin does not prevent gestational diabetes. The report found that although the drug appeared to reduce the risk for late miscarriage and preterm birth in PCOS, the percentage of women taking metformin who developed gestational diabetes (25%) approximately matched that of women taking a placebo (24%). [97]

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