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Date of issue: January 2023, Version: 3.1

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A corresponding patient information leaflet on TREATMENT OF THREADWORM/PINWORM IN PREGNANCY is available.

Threadworm/pinworm infestation (enterobiasis), unless overwhelming, is not usually considered a serious threat to health, therefore infestation in pregnancy should, if possible, be eradicated by rigorous attention to hygiene for at least six weeks.

Data on first trimester mebendazole use are provided from studies which collectively describe ~1,200 first trimester exposures. The results of these studies do not suggest mebendazole use in pregnancy is associated with an increased risk of congenital malformations overall, or of any specific malformations. No increase in the rate of miscarriage, perinatal death, small for gestational age, or differences in gestational age at delivery were found between exposed and unexposed infants. No studies were identified which investigated neurodevelopment, neonatal complications or carcinogenicity in the offspring.

In the treatment of threadworm/pinworm in pregnancy, mebendazole could be considered after first attempting rigorous hygiene measures. When used in the treatment for hookworm, and if required during the first trimester, the benefits of treatment with mebendazole likely outweigh the risks.

Exposure to mebendazole at any stage in pregnancy would not usually be regarded as medical grounds for termination of pregnancy or any additional fetal monitoring. However, other risk factors may be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments.

This is a summary of the full UKTIS monograph for health care professionals and should not be used in isolation. The full UKTIS monograph and access to any hyperlinked related documents is available to NHS health care professionals who are logged in.

If you have a patient with exposure to a drug or chemical and require assistance in making a patient-specific risk assessment, please telephone UKTIS on 0344 892 0909 to discuss the case with a teratology specialist.

If you would like to report a pregnancy to UKTIS please click here to download our pregnancy reporting form. Please encourage all women to complete an online reporting form.

Disclaimer: Every effort has been made to ensure that this monograph was accurate and up-to-date at the time of writing, however it cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes of the measures recommended. The final decision regarding which treatment is used for an individual patient remains the clinical responsibility of the prescriber. This material may be freely reproduced for education and not for profit purposes within the UK National Health Service, however no linking to this website or reproduction by or for commercial organisations is permitted without the express written permission of this service. This document is regularly reviewed and updated. Only use UKTIS monographs downloaded directly from to ensure you are using the most up-to-date version.