(Date: September 2017. Version: 2)

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 Public Health England 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 a medicine that lowers blood sugar. It is used in the treatment of type 2 diabetes, gestational diabetes (diabetes that occurs during pregnancy), and infertility due to polycystic ovary syndrome (PCOS).

Is it safe to use metformin in pregnancy?

The available studies do not suggest that metformin is harmful to a developing baby in the womb. Poorly controlled diabetes in pregnancy increases the chance of miscarriage, birth defects in the baby, stillbirth, and death of the baby just after delivery. It is therefore important that pregnant women with diabetes receive the correct medication to regulate their blood sugar. The National Institute of Health and Care Excellence (NICE) in the UK recommends that metformin (used either on its own or alongside insulin if necessary) is the medicine of choice to treat diabetes in pregnancy.

The published studies that have investigated the possible effects of metformin use in pregnancy on a baby in the womb are summarised below. 

What if I have already used metformin during pregnancy?

If you have been prescribed metformin do not stop taking it without speaking to your doctor first. If you are taking any medicines it is always a good idea to let your doctor know that you are pregnant so that you can decide together whether you still need the medicines that you are on, or whether you might need to switch to a different medicine.

Can using metformin in early pregnancy cause my baby to be born with birth defects?

A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that some medicines are known to cause birth defects.

Studies of over 800 women who received metformin during the first trimester for diabetes or PCOS have not provided any evidence that it increases the likelihood of birth defects in the baby. In fact, studies have shown that use of metformin to establish good diabetic control lowers the chance of birth defects that occur in babies of women with diabetes.  

Can using metformin in early pregnancy cause miscarriage?

Studies which together included over 800 women with PCOS who were taking metformin in early pregnancy have not shown that they were more likely to have a miscarriage than women not taking metformin.

Can using metformin in pregnancy cause stillbirth?

No studies have specifically investigated the chance of stillbirth following use of metformin in pregnancy. However, a study of over 850 women taking metformin to treat diabetes showed that their babies did not have a higher chance of death either just before or just after delivery compared to babies born to women not using metformin. 

Can using metformin in pregnancy cause preterm birth?

Studies which together included over 1,300 pregnant women with diabetes or PCOS who were taking metformin in pregnancy have not shown that they were more likely to have a preterm birth than women not taking metformin.

Can using metformin in pregnancy cause my baby to be small at birth (low birth weight)?

Studies have investigated over 900 babies born to pregnant women with diabetes or PCOS who were taking metformin in pregnancy. Babies exposed to metformin were no more likely to have a birth weight lower than expected for the stage of pregnancy than babies born to women not taking metformin.

Can metformin cause learning or behavioural problems in the child?

A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

A study of over 230 children who had been exposed in the womb to metformin found that their development at age 2.5 years or younger did not differ from that of children not exposed in the womb to metformin. Problems with learning may not always be picked up until children are older. Larger studies specifically designed to assess learning and behaviour in children exposed to metformin in pregnancy are therefore required to answer this question.

Will 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 your baby. However, if you have diabetes during pregnancy your baby’s growth may be more closely monitored as babies born to diabetic women are more likely to be larger than average. Women who were diabetic before becoming pregnant should be under the care of specialist obstetricians with expertise in this area.

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

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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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