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Metformin During Pregnancy Does Not Lower Infant Birth Weight

Jul 24, 2015

Study finds diabetes drug does not prevent macrosomia when given to obese women during pregnancy….

Maternal obesity increases the risk of higher infant birth weights as well as complications such as preeclampsia, cesarean section delivery, maternal hemorrhage, infant mortality and stillbirth. Additionally, infants born with higher fat mass are at risk later in life for obesity, diabetes, and all-cause mortality.


Researchers at the University of Edinburgh postulated that maternal insulin resistance and hyperglycemia along with infant hyperinsulinemia were the cause of obese women’s tendency to have large babies. They designed a study to determine if metformin given during pregnancy could reduce maternal blood sugar, and in turn reduce infant birth weight and pregnancy complications.

Between February 3, 2011 and January 16, 2014, 449 pregnant women with a BMI of 30 or greater and normal glucose tolerance were randomly assigned to receive 500 milligrams of metformin up to five times daily from 16 weeks gestation to delivery or placebo. Results showed that while the maternal blood glucose of the metformin group was lower, there was ultimately no difference in birth weight between the metformin group and the control group (p = 0.7597). Additionally, there was no difference in miscarriage, stillbirth, and neonatal death between the two groups (p = 0.11).

The study did find significant differences in the inflammatory blood markers C-reactive protein, IL-6, and serum cortisol between the two groups (p values 0.04, 0.01, and 0.05, respectively). The researchers suggest that reducing these inflammatory markers, which are often higher in obese pregnant women than their normal weight counterparts, may be beneficial to reducing other pregnancy complications.

Jane Brewin, Chief Executive at the Tommy’s Center for Maternal and Fetal Health at the University of Edinburgh said, “This study shows us there are no easy answers and we must re-double our efforts to find effective ways to help women who are overweight in pregnancy. We must find ways to encourage women to manage their weight before they become pregnant to minimize the potential for adverse impact on their children.”

The researchers plan to continue to follow the infants born during the study to determine if metformin during pregnancy can reduce the risk factors associated with higher birth weight later in life.

Practice Pearls:

  • Obesity is associated with higher birth weight infants, even to glucose-tolerant mothers.
  • Macrosomia can produce complications during pregnancy, delivery, and post-natal.
  • Metformin does not prevent macrosomia when given to obese women during pregnancy.

Chiswick C, Reynolds RM. “Effect of metformin on maternal and fetal outcomes in obese pregnant women (EMPOWaR): a randomised, double-blind, placebo-controlled trial.” The Lancet Diabetes and Endocrinology. Published online 09 July 2015. University of Edinburgh.

“Obesity drug has no effect on baby birth weights, study finds.” Science Daily. 10 July 2015.