Metformin May Reduce Weight Gain, Risk of Preeclampsia in Obese Pregnant Women

The oral medicine metformin is the most commonly prescribed diabetes drug in the world, with more than 61 million prescriptions filled in 2012 in the United States alone. And according to new research out of King’s Hospital in London, although the medicine does not appear to reduce the risk of having a large baby for obese women, it may help reduce weight gain during pregnancy and cut the risk of a dangerous condition known as preeclampsia.

Metformin works by decreasing the amount of glucose made by the liver and by improving insulin sensitivity in the liver, muscle, and fat cells. Because of this effect on insulin sensitivity and previous research indicating that metformin can reduce weight gain in pregnant women with gestational diabetes, the investigators theorized that the medicine might lower the odds of having a large newborn in obese women (a body-mass index of 35 or more) without diabetes, who are at higher risk of having large babies. About one in three women in the United States is obese.


To test this hypothesis, the researchers randomly assigned obese women in the 12th through 18th week of pregnancy to take either 3.0 grams of metformin or a placebo (inactive treatment) daily until delivery. A total of 202 participants received metformin and 198 received placebo.

The researchers found that the medicine did not reduce the odds of the women having a large baby, with nearly 17% of those receiving metformin having a “large for gestational age” baby (a birth weight in at least the 90th percentile), compared to 15% of those receiving placebo. However, the medicine was found to decrease weight gain during pregnancy by an average of nearly 4 pounds, and those taking metformin also had a substantially lower risk of preeclampsia, with 3% of the metformin users developing the condition compared to 11% of the placebo users. Preeclampsia is a serious pregnancy complication defined by high blood pressure and signs of damage to organ systems such as the kidneys. Left untreated, the condition can be fatal for mother and baby.

“Preeclampsia is one of the important pregnancy complications that we’ve been trying to reduce for decades, with variable success,” noted study author Hassan Shehata, MD.

The researchers note that the study did not have enough participants to definitively prove that metformin cuts preeclampsia risk, and they hope to conduct a future study to address that question.

For more information, see the article “Diabetes Drug May Not Help Obese Women Have Normal-Weight Babies” or the study’s abstract in The New England Journal of Medicine. And to learn more about metformin, see “Metformin: The Unauthorized Biography” by diabetes educator Wil Dubois, BS, AAS, CPT, TPT.

If you live in the area of Anchorage, Alaska, you’ll want to check out the upcoming “Taking Control of Your Diabetes” Health Fair. Bookmark and tune in tomorrow to learn more.

  • So, what is the bioavailability of Metformin during gestation? Will it guarantee that the newborn will not contract gestational diabetes?

    • Stephanie Hill

      Newborns do not contract gestational diabetes: gestational diabetes is a condition which primarily affects the mother. However, if mom has elevated blood sugar levels frequently during her pregnancy, the baby can become macrosomic, which means the baby is unusually large and that the baby’s abdomen can be larger than its head (usually the head is the largest part of the newborn’s body). This can cause problems during delivery. The baby can also have some difficulties shortly after delivery regulating its blood sugar.

      Sorry, I don’t know the answer to the bio-availability question.

      This is one of the better sources of information on gestational diabetes I’ve come across. Maybe it will be helpful.