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(Date of issue: November 2017, Version: 3)

This is a UKTIS monograph for use by health care professionals. For case-specific advice please contact UKTIS on 0344 892 0909. To report an exposure please download and complete a pregnancy reporting form. Please encourage all women to complete an online reporting form.

A corresponding patient information leaflet on metronidazole use in pregnancy is available at


Metronidazole is an antimicrobial agent that is used for prophylaxis and treatment of anaerobic, protozoal, Helicobacter pylori and skin infections. It is commonly prescribed orally or as a gel for treatment of bacterial vaginosis and trichomonal infections. Where oral treatment is deemed appropriate, the manufacturer advises against a single high-dose regimen during pregnancy.

Metronidazole was shown to be mutagenic and carcinogenic in some animal studies. However, available data, which are almost exclusively based on oral exposure, do not indicate an increased risk of congenital malformation, low birth weight, intrauterine death, or neonatal complications with metronidazole use in human pregnancy. Preterm delivery has been reported in women with bacterial vaginosis or trichomoniasis, however the relative contribution of the underlying maternal infection and metronidazole exposure to pregnancy outcome is uncertain and recent studies have not found an association between metronidazole use and preterm delivery. Data on spontaneous abortion are conflicting; a cohort study found no significant increase in risk, whereas a nested case control analysis suggests a possible association with metronidazole treatment in pregnancy.

Where possible, the results of culture and sensitivity tests should be available before making a treatment choice in accordance with local prescribing guidelines. 

Exposure to metronidazole 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 document is regularly reviewed and updated. Only use full UKTIS monographs downloaded directly from to be sure you are using the most up-to-date version. The summaries of these monographs are openly available on

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 health care professionals at

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 or to ensure you are using the most up-to-date version.