(Date: July 2015. 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?

Trastuzumab (Herceptin®) is a type of medicine called a monoclonal antibody and may also be referred to as a biologic. It is used to treat certain types of breast and stomach cancers and works by blocking molecules on the surface of the cancer cells that are important for their growth.

Is it safe to take trastuzumab in pregnancy?

Any woman who is taking trastuzumab and is planning a pregnancy should speak to her doctor to discuss the possibility of switching to a different medicine before she conceives. Use of trastuzumab in the second and third trimesters is not generally advised but may be considered necessary for the treatment of very serious illnesses if other treatments have not worked. Your doctor will be able to help you to weigh up how necessary trastuzumab is to your health against the possible risks to you or your baby, which will depend on how many weeks pregnant you are.

This leaflet summarises the scientific studies relating to the effects of trastuzumab on a baby in the womb. 

What if I have already taken trastuzumab 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 trastuzumab 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.

There are currently no large scientific studies that have investigated whether trastuzumab use during the first trimester of pregnancy can cause birth defects in the baby. There is a small study of 12 babies and case reports of a further five who were born to pregnant women who took trastuzumab in the first trimester, none of whom had birth defects. Although this is reassuring, large scientific studies need to be carried out before we can say whether trastuzumab is safe to use in early pregnancy.

What problems can taking trastuzumab after the first trimester of pregnancy cause in my baby?

Case reports have indicated that taking trastuzumab during the second and third trimesters can cause a reduction in the levels of amniotic fluid around the baby in the womb (oligohydramnios). Reduced amniotic fluid can lead to a number of problems in the baby including:

• Underdevelopment of the skull bones

• Reduced growth in the womb

• Poor development of lungs (because inhaling amniotic fluid while in the womb helps to expand and develop the lungs)

• Kidney problems

• The bladder being underdeveloped (because urine expands and develops the bladder)

• The baby’s skull and leg bones being misshapen and the baby having ‘flattened’ facial features (as a result of there not being enough amniotic fluid to ‘cushion’ the baby in the womb)

Because very few women take trastuzumab during the second and third trimesters of pregnancy, no large studies have been carried out that might tell us what the chances are of a baby exposed to trastuzumab during this period developing the above problems.

Some of the complications described above can be serious and there are reports of babies exposed to trastuzumab during the second or third trimesters dying after birth. However, pregnant women being treated for cancer may be receiving a number of different (often toxic) medicines, and may also be more likely to have very premature babies if induced early delivery is required because of the mother’s health. This may also contribute to the risk of a baby dying after birth.

Low levels of amniotic fluid can be detected by ultrasound scans. If low amniotic fluid levels are identified early enough and treatment with trastuzumab is able to be stopped, the effects listed above may be prevented and some may be reversible. Regular monitoring of your baby will therefore be required to allow ongoing decisions to be made about the best treatment for you and your baby’s health. Please discuss any concerns that you may have with your doctor.

Can taking trastuzumab in pregnancy cause miscarriage?

To date, no large scientific studies have specifically assessed miscarriage rates in pregnant women taking trastuzumab. Early reports to the manufacturer of 271 pregnant women who took trastuzumab do not suggest that the occurrence of miscarriage was increased. Although a clinical trial found that 16 women who took trastuzumab during the first trimester of pregnancy had a higher chance of miscarriage compared to women who did not take trastuzumab, the chance of having a miscarriage in women taking trastuzumab was still similar to that in the background population. Further scientific research is, however, required to determine whether use of trastuzumab in early pregnancy increases the chance of miscarriage.

Can taking trastuzumab in pregnancy cause stillbirth?

No studies have specifically analysed stillbirth rates in pregnant women taking trastuzumab.

Can taking trastuzumab in pregnancy cause preterm birth, or my baby to be small at birth (low birth weight)?

No studies have specifically analysed whether preterm birth or low birth weight babies are more common in pregnant women taking trastuzumab. There are case reports of babies who were exposed to trastuzumab in the womb being born preterm (which itself increases the chance of a baby having a low birth weight), but many of these babies were born by induced early delivery, either due to illness in the mother or because reduced amniotic fluid had been detected. It is therefore unclear whether taking trastuzumab in pregnancy can directly cause premature birth or low birth weight in the baby.

Can taking trastuzumab in pregnancy cause learning and 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 have been carried out to specifically investigate whether exposure to trastuzumab while in the womb increases the chance of learning and behavioural problems in the child. A handful of case reports describe normal development up to five years of age in children who were exposed to trastuzumab in the womb, but larger scientific studies are needed to study this accurately.

Will I or my baby need extra monitoring during pregnancy?

Most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects as part of their routine antenatal care.

Because the effects of taking trastuzumab in early pregnancy are largely unknown, your doctor may suggest extra monitoring of your baby, including more detailed scans for birth defects and monitoring of your baby’s growth in the womb. If you have taken trastuzumab during the second or third trimesters, extra scans to monitor levels of amniotic fluid will be required. 

Pregnant women taking trastuzumab are likely to receive heart monitoring as treatment with trastuzumab is associated with an increased risk of heart failure. Women with the illnesses that trastuzumab is used to treat may also be more closely monitored during pregnancy to ensure that they remain well throughout, and that their baby is growing and developing as expected. 

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

Most experts agree that the majority of medicines used by the father are unlikely to harm the baby through effects on the sperm. However, more research on the effects of trastuzumab specifically and medicine use in men around the time of conception generally is needed.

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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