Treatment of threadworms during pregnancy

(Date: January 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 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 are threadworms?

Threadworms are parasitic worms that live in the bowel and lay their eggs around the anus at night, causing itching. Threadworms are common in young children. Because threadworms are extremely contagious, if one member of your household has threadworms, everyone in the household should be treated, even if they are not showing symptoms.

How are threadworms spread?

Scratching or touching an infected anus can spread threadworms eggs onto surfaces, clothes and bed linen, where they can survive for up to three weeks. These eggs can infect others who unknowingly touch them and transfer them to their mouths. Swallowed eggs hatch into worms inside the bowel. After about two weeks the hatched worms begin to lay their own eggs, starting the cycle again.

How do I treat threadworms during pregnancy?

Threadworm infection during pregnancy is not known to put your unborn baby at any risk. Pregnant women may be able to avoid taking medicines to treat threadworms by using strict hygiene measures to clear themselves. Threadworms already in the bowel die within approximately six weeks. If you or someone you live with is diagnosed with threadworms, the following measures should be followed strictly for at least six weeks to ensure that you do not swallow any new eggs:

• Wash all soft toys, clothes, bed linen and night clothes in one go. Avoid shaking these items as you handle them and wash your hands carefully afterwards.
• Regularly vacuum and damp-dust your home, particularly the bedrooms.
• Regularly clean the kitchen and bathroom thoroughly.
• Don’t eat in the bedrooms.
• Keep fingernails short and avoid putting your (or your children’s) fingers in your mouth.
• Ensure everyone washes their hands frequently and scrubs under fingernails, particularly before eating, after going to the toilet, and after changing nappies.
• Wear close-fitting underwear at night and change your underwear every morning.
• Bathe or shower each morning and do not share wash cloths or towels.
• Keep toothbrushes in a closed cupboard and rinse before use.

What if hygiene measures don’t clear my threadworms on their own?

If the above measures do not clear up a threadworm infection your doctor may suggest a medicine that treats parasitic worm infections. The only such medicine currently available in the UK is mebendazole (Vermox,® Ovex,® Benda®).

Mebendazole kills adult worms but not the eggs, so when you are treated for threadworms, the hygiene measures described above still need to be followed for at least three weeks to ensure that you are not re-infected with new eggs.

Is there any risk to my baby from use of mebendazole in pregnancy?

Studies that included around 1,650 women taking mebendazole during the first trimester of pregnancy found that these women do not seem to have a higher chance of having a baby with a birth defect.

Studies of a small number of pregnant women taking mebendazole in early pregnancy have shown no link with miscarriage.

A study of around 2,500 pregnant women taking mebendazole did not shown any links with stillbirth, premature delivery (before 37 weeks of pregnancy), very low birth weight in the baby (less than 1,500g), or the baby dying soon after birth.

While these studies are reassuring, more information about women who have taken mebendazole in early pregnancy and their babies needs to be collected. Because there is little information on the safety of mebendazole in pregnancy, where possible, hygiene measures should be tried first to treat threadworms in early pregnancy and mebendazole only used after the first 12 weeks of pregnancy.

Will my baby need extra monitoring during pregnancy?

As part of their routine antenatal care, most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects and to check the baby’s growth.

Taking mebendazole during pregnancy is not expected to cause any problems that would require extra monitoring of your baby. 

Are there any risks to my baby if the father has used anthelmintics?

We would not expect any increased risk to your baby if the father used mebendazole before or around the time your baby was conceived.

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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