(Date: May 2017. 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.

What is it?

Pyridostigmine is a medicine that is most commonly used to treat an illness called myasthenia gravis.

Can myasthenia gravis affect my pregnancy?

Myasthenia gravis (MG) is an auto-immune illness which causes muscle weakness. This is due to molecules in the immune system called antibodies mistakenly blocking communication between muscles and nerves. During pregnancy these antibodies can cross the placenta and have a similar effect in the developing baby. If the baby cannot move freely in the womb due to muscle weakness the development of its joints and muscles may be permanently affected. Babies of women with MG may therefore be born with their limb joints fixed in a bent position, a condition called arthrogryposis multiplex congenita (AMC). Babies with AMC are more likely to be stillborn.

In the UK, women with MG should be offered specialist care during pregnancy. Medicines that suppress the immune system, such as corticosteroids or azathioprine, may be recommended both to treat the mother and to reduce the risk of AMC in the baby. For more information on use of these medicines see the bump leaflets on use of corticosteroids in pregnancy and use of azathioprine in pregnancy.

Is it safe to take pyridostigmine in pregnancy?

It is not possible to answer this question as pyridostigmine use in pregnancy has not been well studied. However, myasthenia gravis can be a serious illness and it is important that women with the condition receive appropriate treatment. Any assessment of safety needs to weigh up the risks and benefits of stopping the treatment against those of continuing treatment. The outcome of this assessment will vary from person to person and will depend on the severity of the mother’s illness and the complications that could arise if her treatment is altered.

When deciding whether to use pyridostigmine during pregnancy it is therefore important to weigh up how necessary it is to your health against any possible risks to you or your baby, some of which might depend on how many weeks pregnant you are.

This leaflet summarises the available information relating to the effects of pyridostigmine on a baby in the womb.

What if I have already taken pyridostigmine during pregnancy?

If you are taking 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 or whether you might need to switch to a different medicine.
If you have myasthenia gravis it is important to let your doctor know as soon as possible that you are pregnant so that any additional monitoring of you and your pregnancy can be arranged if needed, and additional medicines can be prescribed if necessary.

Can taking pyridostigmine 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 pyridostigmine use during the first trimester of pregnancy can cause birth defects in the baby. We have been able to identify case studies of 29 babies who were born to pregnant women who took pyridostigmine in the first trimester. Four of these babies had birth defects, but these were thought to have been due to myasthenia gravis itself rather than to any medicines taken by the mother. Although these reports do not raise any concerns, information on many more pregnancies needs to be collected before it is possible to accurately assess whether pyridostigmine causes birth defects.

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

No studies have specifically analysed whether these outcomes are more or less common in pregnant women taking pyridostigmine.

Can taking pyridostigmine 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 pyridostigmine exposure in the womb might affect a child’s learning and behaviour. This is the case for most medicines.

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 pyridostigmine in early pregnancy are largely unknown, your doctor may suggest extra monitoring of your baby, including more detailed or earlier scans to detect birth defects, and more frequent review of your baby’s growth in the womb.

Women with myasthenia gravis will also be more closely monitored during pregnancy to assess their health throughout and to check that their baby is growing and moving as expected. 

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

There are no scientific reports of babies born to men who were treated with pyridostigmine around the time of conception. 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 pyridostigmine 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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