(Date: May 2016. 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?

Sirolimus is a medicine that suppresses the immune system. It is most commonly used to prevent organ rejection in people who have had a kidney transplant.

Is it safe to take sirolimus in pregnancy?

There is very little information available about whether it is safe to use sirolimus in pregnancy (see below). Any woman who is taking sirolimus and is planning a pregnancy should therefore speak to her doctor to discuss the possibility of switching to a different medicine before she conceives. However, this may not be advisable for everyone and use of sirolimus in pregnancy may sometimes be considered necessary to prevent the rejection of a transplanted organ.

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

What if I have already taken sirolimus 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, that you are taking the lowest dose that works, or whether you might need to switch to a different medicine.

Can taking sirolimus 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 sirolimus use during the first trimester of pregnancy can cause birth defects in the baby. The only information available at present consists of case reports in medical journals of 23 babies who were born to pregnant women who took sirolimus in the first trimester. Two of these babies had different types of birth defect. Although this provides no evidence that sirolimus use in early pregnancy causes birth defects in the baby, it also does not provide evidence that it does not. Large, carefully designed scientific studies need to be carried out before we can say whether sirolimus is safe to use in early pregnancy.

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

No studies have specifically analysed rates of these outcomes in pregnant women taking sirolimus.

Can taking sirolimus 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 investigate whether sirolimus exposure in the womb might affect a child’s learning and behaviour. Research is required to determine whether exposure in the womb might affect a child’s learning or behaviour.

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 sirolimus 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.

Women who have previously received an organ transplant will 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 sirolimus?

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 sirolimus specifically, and the fetal effects of 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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