(Date: October 2022. Version: 4)

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.

Quick read

It is very important to correctly treat an infection in pregnancy. Metronidazole may be recommended for some types of infection where the benefits of treatment are thought to outweigh the possible risks.

What is it?

Metronidazole (Flagyl®) is used to treat a number of infections, including skin infections, dental infections, and bacterial vaginosis. It is also used to eradicate a type of stomach bacteria called Helicobacter pylori, which can cause stomach ulcers.

What are the benefits of taking metronidazole in pregnancy?

Metronidazole treatment can reduce unpleasant symptoms and prevent serious complications from an infection, including some pregnancy problems.

Are there any risks of taking metronidazole in pregnancy?

Metronidazole use in pregnancy has been well studied and is not known to cause birth defects, stillbirth, low birth weight, or preterm delivery. Although some studies have shown that miscarriage might be more common in women taking metronidazole in early pregnancy, it is unclear if the increased risk might be caused by the infections that metronidazole was being used to treat.

Are there any alternatives to taking metronidazole in pregnancy?

Possibly, although alternative antibiotics may not work as well as metronidazole for some types of infection. A doctor or midwife will be able to discuss why a particular antibiotic is advised as the best treatment.

What if I prefer not to take medicines in pregnancy?

It is important that an infection in pregnancy is well-treated as it can lead to very unpleasant symptoms, as well as serious complications for both mother and baby.

A doctor will only prescribe medicines when necessary and will be happy to talk about any concerns.

Will I or my baby need extra monitoring?

As part of routine antenatal care in the UK, women are invited for a very detailed scan at around 20 weeks of pregnancy to check the baby’s development. No further monitoring is required for women taking metronidazole.

Are there any risks to my baby if the father has used metronidazole?

There is no evidence that metronidazole used by the father can harm the baby through effects on the sperm.

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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