(Date: November 2017. 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 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?

Metronidazole (Flagyl®) is an antimicrobial medicine commonly prescribed to treat vaginal infections, skin and dental infections, and Helicobacter pylori, the bacterium that is linked to stomach ulcers.

Is it safe to use metronidazole in pregnancy?

The timely and correct treatment of potentially severe bacterial infections during pregnancy may be crucial to the health of both mother and baby. Additionally, some untreated vaginal infections during pregnancy may increase a woman’s chance of going into premature labour.

When deciding whether or not to take metronidazole during pregnancy it is important to weigh up how necessary this is to your health against the possible risks to you or your baby, some of which will depend on how many weeks pregnant you are. Your doctor is the best person to help you decide what is right for you and your baby.

What if I have already taken metronidazole during pregnancy?

If you have taken 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 and to make sure that you are taking the lowest dose that works.

Can taking metronidazole in 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.

No increased chance of birth defects overall was shown in seven of eight large studies of children exposed to metronidazole in the womb. Taken together, the information from three studies that investigate the chance of specific birth defects following exposure in the womb to metronidazole does not provide convincing evidence of any links. However, to confirm this, more studies of this type ideally need to be carried out.

Can taking metronidazole in pregnancy cause miscarriage?

While no increased chance of miscarriage in pregnant women who had taken metronidazole was identified in one study, one further study did identify a possible link between miscarriage and use of metronidazole in early pregnancy. It is unclear whether this might have been due to the infections that the women were taking metronidazole to treat rather than to a specific effect of the medicine. Because limited numbers of women taking metronidazole have been studied, more information is needed before firm conclusions can be drawn.

Can taking metronidazole in pregnancy cause preterm birth?

No increased chance of having a premature baby (born before 37 weeks) in mothers who had taken metronidazole during pregnancy was found in all of the three studies that have looked at this.

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

Three out of four studies have shown no link between taking metronidazole during pregnancy and reduced birth weight in the baby.

Can taking metronidazole in pregnancy cause stillbirth?

No increased chance of stillbirth in the babies of mothers taking metronidazole during pregnancy was found in the two studies that have investigated this outcome.

Can taking metronidazole in pregnancy 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.

No studies of learning and behaviour in children exposed in the womb to metronidazole have been carried out.

Will my baby need extra monitoring during pregnancy?

As part of their routine antenatal care, most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects and to check the baby’s growth.

There is no evidence that taking metronidazole during pregnancy causes any problems that would require extra monitoring for your baby.

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

We would not expect any problems for your baby caused by the father taking metronidazole before or around the time you became pregnant.

Alcohol and metronidazole

Consumption of even tiny amounts of alcohol while taking metronidazole can result in unpleasant side effects including nausea, vomiting, flushing of the skin, increased heart rate and shortness of breath. Anyone taking metronidazole should avoid alcohol completely, and this is especially important during pregnancy.

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 healthcare 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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