(Date: April 2022. Version: 3)

This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by the UK Health Security Agency (UKHSA) on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during pregnancy.

What is it?

Metformin is mainly used to treat type 2 diabetes and gestational diabetes.

What are the benefits of using metformin in pregnancy?

Metformin helps to control blood sugar levels in people with diabetes. Good blood sugar control is essential to reduce the likelihood of ill-effects caused by diabetes including damage to the blood vessels, nerves, and eyes.

Poorly controlled type 2 diabetes in pregnancy increases the chance of miscarriage, birth defects in the baby, stillbirth, and death of the baby just after delivery.

Poorly controlled gestational diabetes is linked to having a bigger baby, delivery complications and problems with the baby’s blood sugar levels after birth.

What are the risks of using metformin during pregnancy?

There are no known risks of using metformin in pregnancy.

Are there any alternatives to using metformin in pregnancy

Not usually — metformin is generally the first-choice drug for treatment of diabetes in pregnancy.

Women who are taking metformin before pregnancy will likely be advised to continue, as this tends to be safest for both mother and baby.

Some women may also need to use insulin alongside metformin to ensure good blood sugar control.

Women using metformin who are planning a pregnancy or become pregnant should let their doctor know — they will assess whether it needs to be continued and ensure the dose is correct.

What if I prefer not to use metformin in pregnancy?

It is very important that blood sugar levels are well-controlled in pregnancy to avoid adverse effects for both mother and baby. Using metformin is often the safest way to ensure this.

Are there any risks to my baby if the father uses metformin?

A study published in 2022 found a possible link between use of metformin by the father around the time of conception and genital malformations in male babies. However, diabetes itself is known to affect sperm quality and further research is required to find out if the effects seen in male babies are caused by metformin or by diabetes/poor blood sugar control in the father.

Will I or my baby need extra monitoring during pregnancy?

Use of metformin during pregnancy is not expected to cause any problems that would require extra monitoring of the baby.

Pregnant women with diabetes are more likely to have a larger than average baby — extra monitoring of their baby’s growth will therefore be offered.

Who can I talk to if I have questions?

If you have any questions regarding the information in this leaflet, please discuss them with your health care provider. They can access more detailed medical and scientific information from

How can I help to improve drug safety information for pregnant women in the future?

Our online reporting system allows women with a current or previous pregnancy to create a digitally secure ‘my bumps record’. You will be asked to enter information about your health, whether or not you take any medicines, and your pregnancy outcome. You can update your details at any time during pregnancy or afterwards. This information will help us better understand how medicines affect the health of pregnant women and their babies. Please visit to register.

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General information 

Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks.  They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.

Medicines use in pregnancy

Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby.  There are, however, some medicines that can harm a baby’s normal development.  How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.

If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.

When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.   

Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider. It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.

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