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(Date of issue: July 2015, Version: 2)

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 natalizumab use in pregnancy is available at


Natalizumab is a recombinant humanised anti-α4-integrin antibody licensed for the treatment of highly active relapsing remitting multiple sclerosis.

A critical step in the inflammatory process underlying multiple sclerosis (MS) involves immune cell trafficking into the CNS via the blood-brain barrier. The presence of the α4-integrin protein on the surface of immune system lymphocytes is integral to assisting such diffusion. Treatment with natalizumab inhibits α4-integrin activity, thereby reducing the rate of lymphocyte transfer into the CNS.

Data on the use of natalizumab in pregnancy is extremely limited and is currently insufficient to evaluate any risks posed to the fetus. Current pregnancy data consists of only 31 first trimester exposures. Although there is currently no signal that natalizumab is a major structural teratogen, the available data are too limited to exclude an increased risk of malformation or other adverse pregnancy outcome.

Use of natalizumab amongst non-pregnant patients has been associated with an increased risk of progressive multifocal leukoencephalopathy (PML) as a result of reactivation of the commonly carried dormant Polyomavirus JC. Given that maternal physiological immunosuppression occurs naturally during pregnancy, pregnant patients being treated with natalizumab may be at even greater risk of PML. The subsequent transmission of the Polyomavirus JC to the fetus may be of further concern. Due to the limited experience of natalizumab use in pregnancy, data investigating both the risk of PML development amongst pregnant patients and the risk of viral transmission to the fetus is currently unavailable.

Where treatment with natalizumab is clinically indicated during pregnancy, close monitoring of maternal neurological function is advised. Should maternal symptoms of PML present during pregnancy, enhanced fetal and neonatal monitoring may also be warranted.

This document is regularly reviewed and updated. Only use UKTIS monographs downloaded directly from or to be sure you are using the most up-to-date version.

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.