Paternal exposure

(Date: April 2018. 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 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.

Medicines used by men around the time of conception

Although an increasingly common question, very little research has been carried out to answer whether medicines taken by a man around the time of conception can impact on a baby’s development.

Sperm cells take around three months to fully develop. Therefore, in theory, use of medicines by a man during the previous three months could cause changes to the genetic code in sperm. It has long been questioned as to whether these genetic changes could alter the health of a baby during development in the womb, or later on in life.

Concerns have also been raised about the possibility that medicines that are known to be harmful to a developing baby when taken during pregnancy could be passed on to a pregnant women and therefore her baby via semen during sexual intercourse.

Encouragingly, the small amount of information that is available does not suggest that medication used by the father at the time of conception causes any major harm to a baby. There are, however, some medicines that are considered to be risky, mostly because they are known to cause genetic faults. Attempting pregnancy is not advised while these medicines are being taken by the father, and for six months after he stops taking them. It is therefore important that a man planning on fathering a pregnancy requests information specific to the medicine that he is taking, or if there are concerns regarding pregnancy following a paternal exposure. A section on paternal exposure is included in each of our bumps leaflets. 

Can medicine use affect male fertility?

Some medicines can affect male fertility by reducing the sperm count or affecting the way that sperm move and swim (sperm motility); other medicines affect the amount of semen produced. Some medicines can also affect a man’s libido (sex drive) or cause erectile dysfunction. These effects usually disappear once the medicine is stopped.

Which medicines may be unsafe to use in men planning to father a pregnancy?

Men using certain medicines that are known to alter the genetic code (DNA) are usually advised by their doctor or specialist to wait at least six months after stopping the medicine before attempting to father a pregnancy. Such medicines include chemotherapy drugs, medicines used in the treatment of inflammatory or auto-immune disease, or to prevent the rejection of a transplanted organ (for example, methotrexate, mycophenolate mofetil, leflunomide, azathioprine and mercaptopurine).

Waiting for six months before attempting pregnancy is advised so that conception occurs by sperm that have not been exposed to the drug. Fortunately, no clear adverse effects on pregnancy outcomes have been shown among the small number of pregnancies to men who were still taking their medication at the time of conception or in the six months before. However, because only small numbers of men taking these medicines have been studied, further research is still required before this guidance can be challenged.

What if my partner is already pregnant?

If conception occurred while the father was taking a medicine for which a six month waiting period is advised, you should tell your doctor. Although it is unlikely that any additional monitoring of the pregnancy/baby will be required, it may be important for future knowledge that this information is recorded in your notes.

A number of medicines are known or suspected to increase the risk of birth defects in babies born to women who use them in early pregnancy. Examples include thalidomide, mycophenolate mofetil and leflunomide. Men taking these medicines during a partner’s pregnancy may be advised by their doctor/specialist to use condoms or avoid sexual contact. This is because, in theory, these drugs could pass into the semen and be absorbed into the mother’s bloodstream, or pass through her cervix following sexual contact and could reach the baby in the womb. In practice, it is considered very unlikely that drugs in semen could reach a baby in the womb in amounts large enough to cause damage.

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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