Metformin and its effects in pregnancy

Marian Aldhous, Rebecca Reynolds, Jane Norman

Scientists have found that there are no harmful effects on mums who take the drug metformin during pregnancy.

This research is now complete

One of the effects of obesity during pregnancy is giving birth to heavy babies. Earlier work supported by Tommy’s showed that large babies can be more likely to be obese or have heart disease when they grow up. A large baby may also be difficult to deliver.

Scientists have been trying to understand how obesity during pregnancy causes effects in children. A previous trial that was carried out in a Tommy's centre, called EMPOWaR (Effect of Metformin on maternal and fetal outcomes in Pregnant Obese Women: a Randomised double-blind, placebo controlled trial, tested whether a drug called metformin could help obese women give birth to lighter babies and so reduce complications at birth.

Metformin is usually used to treat diabetes that is diagnosed during pregnancy (gestational diabetes). Women with diabetes have something in common with pregnant obese women: the level of glucose in their blood is often too high. Scientists thought that metformin might help lower the amount of glucose in the blood of obese pregnant women, and in turn help lower the birth weight of their babies. 

Even though the EMPOWaR trial did not show a difference in babies' birth weights, it is possible that metformin has had other effects that on the babies' health. Scientists took samples of placenta from 125 women and looked to see if the samples from women who had taken metformin were different from those who hadn't. They found no difference between women who took metformin and those who didn't. However, there were differences in the activity of genes depending on how the baby was delivered, whether the mother developed diabetes, and the gender of the baby.

The results suggest that there are no harmful effects from metformin on which genes are active in the placenta. This is reassuring, as metformin is widely used in pregnancy.

What we’re doing next

Following on from our previous research, we want to understand more about the effects of metformin on child development.  

We will be looking at children born to mothers who took metformin during pregnancy, to see if there are any long term effects. 

To do this, we will be following up with the women who took part in our EMPOWaR trial when they were pregnant. We will be inviting the participants and their children (who are now around five years old) to take part in our follow-up study.  

Our findings will give us a great insight into the long-term effects of metformin on child development.



Thanks for your interest in our research

Tommy's funds research across the UK investigating the reasons for pregnancy complications and loss. Maternal and fetal research is underfunded and we need your support to continue. There are many small and large ways you can support us, find out more here.


This study takes place in a Tommy's centre and is funded by Tommy's and the Medical Research Council and National Institute for Health Research's Efficacy and Mechanism Evaluation Programme

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