(Date: May 2015. Version: 1)

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?

Ustekinumab (Stelara®) is a type of medicine called a monoclonal antibody and may also be referred to as a biologic. It works by blocking molecules in the immune system that cause inflammation. It is therefore prescribed to treat certain auto-immune conditions including psoriasis and psoriatic arthritis (a type of arthritis that develops in some people with psoriasis).

Is it safe to take ustekinumab in pregnancy?

There is no yes or no answer to this question. Ustekinumab is quite a new medicine and so far no studies have investigated whether it is safe to use during pregnancy. When deciding whether to take ustekinumab during pregnancy it is important to weigh up how necessary ustekinumab is to your health against any possible risks to you or your baby, some of which may 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.

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

What if I have already taken ustekinumab 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 ustekinumab 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.

There are currently no scientific studies that have investigated whether ustekinumab use during pregnancy increases the risk of birth defects in the baby. Although there are case reports of six non-malformed babies being born to pregnant women who took ustekinumab, large scientific studies need to be carried out before we can say whether ustekinumab is safe to use in pregnancy.

It is known that ustekinumab cannot cross the placenta in early pregnancy and is therefore unlikely to have any direct effects on a developing baby. However, some medicines can indirectly affect the way that an unborn baby grows and develops, for example by affecting the mother’s circulatory system or the function of the placenta. Studies of the pregnancy safety of ustekinumab are therefore required.

Can taking ustekinumab in pregnancy cause miscarriage?

Studying miscarriage rates in women taking ustekinumab and other monoclonal antibodies is complex as some of the mother’s illnesses that these medicines are used to treat are known to increase the chance of miscarriage.

To date, no studies have specifically assessed miscarriage rates in pregnant women taking ustekinumab and scientific research into this subject is therefore required.

Can taking ustekinumab in pregnancy cause stillbirth?

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

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

Some of the underlying illnesses that ustekinumab and other monoclonal antibodies are used to treat may themselves increase the chance of preterm birth (before 37 weeks) and/or of a baby having a low birth weight. It is therefore very difficult to say whether ustekinumab might have an effect on these outcomes and no studies have investigated this so far.

Can taking ustekinumab in pregnancy cause other health problems in the child?

Learning and behavioural problems
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 link with learning and behavioural problems e.g. autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) is known about in children who were exposed to ustekinumab while in the womb, however no studies have been carried out to specifically investigate this.

Infections and live vaccines in the baby after birth 
Monoclonal antibodies such as ustekinumab work by reducing or inactivating molecules in the body that are important to fight off infections. There are therefore concerns that babies who are exposed to ustekinumab in the womb may be more likely to develop infections after birth. No studies have assessed infection risk in babies specifically exposed in the womb to ustekinumab. One study of babies exposed to a similar medicine did not find any evidence that exposure was linked to an increased risk of infection in the child after birth, but the findings of this study may not be directly relevant to women taking ustekinumab. Studies of babies who were exposed in the womb to ustekinumab are therefore required.

There are also concerns that babies who are exposed to ustekinumab in the womb could become ill if they receive a live vaccine. Live vaccines (e.g. rubella, measles, mumps, rotavirus) contain modified versions of the live viruses or bacteria that they protect against. They do not cause illness in people with healthy immune systems but are often not advised in people with low immunity. As a precaution, your doctor may suggest that your baby does not receive any live vaccines for a few months after your final pregnancy dose of ustekinumab.

Will 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 ustekinumab is a new medicine and the effects of taking it in pregnancy are 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. Women with some of the illnesses that ustekinumab 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 ustekinumab?

Most experts agree that the majority of medicines used by the father are unlikely to harm the baby through affects on the sperm. However, more research on the effects of ustekinumab 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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