Date: May 2022, Version 4

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.

No treatment

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 (MyBump Portal) allows women who are currently pregnant to create a secure record of their pregnancy, collected through a series of questionnaires. You will be asked to enter information about your health, whether or not you take any medicines, your pregnancy outcome and your child's development. 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 the MyBump Portal to register.

General information
Sadly, miscarriage and birth defects can occur in any pregnancy.

Miscarriage occurs in about 1 in every 5 pregnancies, and 1 in every 40 babies are born with a birth defect. This is called the ‘background risk’ and happens whether medication is taken or not.

Most medicines cross the placenta and reach the baby. For many medications this is not a problem. However, some medicines can affect a baby’s growth and development.

If you take regular medication and are planning to conceive, you should discuss whether your medicine is safe to continue with your doctor/health care team before becoming pregnant. If you have an unplanned pregnancy while taking a medicine, you should tell your doctor as soon as possible.

If a new medicine is suggested for you during pregnancy, please make sure that the person prescribing it knows that you are pregnant. If you have any concerns about a medicine, you can check with your doctor, midwife or pharmacist.

Our Bumps information leaflets provide information about the effects of medicines in pregnancy so that you can decide, together with your healthcare provider, what is best for you and your baby.