(Date: May 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.

What is it?

Trastuzumab is an antibody therapy used to treat breast and stomach cancers.

What are the benefits of using trastuzumab in pregnancy?

Trastuzumab can reduce certain types of tumour growth. It is only used in pregnancy when the benefits to the mother’s health outweigh the possible risks to the baby.

What are the risks of using trastuzumab in pregnancy?

Very few pregnant women taking trastuzumab have been studied. The available information does not link trastuzumab use to miscarriage or birth defects. Ongoing data collection is needed to determine whether trastuzumab is safe to take in early pregnancy.

Trastuzumab used in later pregnancy can reduce the amount of fluid around the baby in the womb. This can be linked to problems with the baby’s lungs and kidneys. It also increases the chance of the baby being born preterm, which itself poses some risks.

Are there any alternatives to using trastuzumab in pregnancy?

Possibly. Switching to a different drug or having a break from treatment may be an option for some women. However, if trastuzumab was working before pregnancy and there is a high chance of relapse without trastuzumab, it may be advisable to continue taking it.

Women who accidentally conceive while taking trastuzumab should arrange to see their doctor or specialist as soon as possible to make sure that trastuzumab is still the best treatment and the dose is correct.

What if I prefer not to take trastuzumab during pregnancy?

If a woman is advised to continue trastuzumab in pregnancy, this is because she could become seriously unwell without it.

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

Will I or my baby need extra monitoring?

As part of routine antenatal care, most women will be offered a very detailed scan at around 20 weeks of pregnancy to check the baby’s development. No further scans to check for birth defects will be required. However, because trastuzumab used in later pregnancy can affect the amniotic fluid level, additional monitoring of this, along with the baby’s growth and wellbeing, will be recommended.

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

There is currently no evidence that trastuzumab 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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