Date: January 2018, Version 2

Quick read

Having threadworms in pregnancy does not harm the baby. Threadworms in pregnancy can be treated using hygiene measures, or with a medicine called mebendazole. Hygiene measures may be preferred in early pregnancy while the baby is developing.

What are threadworms?

Threadworms infect the bowel and cause itching of the anus (bottom). They are common in young children and spread very easily between household members. Threadworms during pregnancy can be unpleasant and might affect sleep due to itching but do not directly harm the baby.

How do I treat threadworms during pregnancy?

Pregnant women may be able to avoid taking medicines to treat threadworms by using strict hygiene measures to clear them. For details of these hygiene measures, please see the NHS information on Threadworms.

If hygiene measures do not clear up threadworms, or medicine use is preferred, mebendazole (Vermox®, Ovex®) can be used. There is no evidence that mebendazole harms the baby, and it is only absorbed into the body in small amounts. However, some women may prefer to try hygiene measures first and delay mebendazole treatment until the baby is fully developed at around 12 weeks of pregnancy.

Will my baby need extra monitoring?

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.

Having threadworms or 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 mebendazole?

We would not expect any increased risk to your baby if the father had threadworms or 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

How can I help to improve drug safety information for pregnant women in the future?

Our online reporting system (MyBump Portal) allows women who are currently pregnant to create a secure record of their pregnancy, collected through a series of questionnaires. You will be asked to enter information about your health, whether or not you take any medicines, your pregnancy outcome and your child's development. You can update your details at any time during pregnancy or afterwards. This information will help us better understand how medicines affect the health of pregnant women and their babies. Please visit the MyBump Portal to register.

General information
Sadly, miscarriage and birth defects can occur in any pregnancy.

Miscarriage occurs in about 1 in every 5 pregnancies, and 1 in every 40 babies are born with a birth defect. This is called the ‘background risk’ and happens whether medication is taken or not.

Most medicines cross the placenta and reach the baby. For many medications this is not a problem. However, some medicines can affect a baby’s growth and development.

If you take regular medication and are planning to conceive, you should discuss whether your medicine is safe to continue with your doctor/health care team before becoming pregnant. If you have an unplanned pregnancy while taking a medicine, you should tell your doctor as soon as possible.

If a new medicine is suggested for you during pregnancy, please make sure that the person prescribing it knows that you are pregnant. If you have any concerns about a medicine, you can check with your doctor, midwife or pharmacist.

Our Bumps information leaflets provide information about the effects of medicines in pregnancy so that you can decide, together with your healthcare provider, what is best for you and your baby.