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Date of issue: December 2023, Version: 3

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A corresponding patient information leaflet on USE OF VITAMIN B12 IN PREGNANCY is available.

Vitamin B12 refers to a group of cobalt-containing vitamers including, hydroxocobalamin and cyanocobalamin. Both of these forms of vitamin B12 have been used in the prophylaxis and treatment of anaemia due to vitamin B12 deficiency. Hydroxocobalamin is also used in much higher doses as an antidote for cyanide poisoning. No specific UK guidelines regarding vitamin B12 supplementation during pregnancy currently exist. The Royal College of Obstetricians and Gynaecologists (RCOG) does not recommend routine supplementation of B vitamins (with the exception of folic acid) during pregnancy.

Vitamin B12 is naturally occurring in many foods derived from animal sources. Women who follow a vegan diet may be at an increased risk of being vitamin B12 deficient and should ensure adequate intake of vitamins and minerals.

There are limited published data regarding the use of supplemental vitamin B12 (in any form) during pregnancy; however, there is no evidence or reason to expect that use would be associated with an increased risk of congenital malformation or other adverse fetal effects. High maternal vitamin B12 concentrations have been associated with autism spectrum disorder in the offspring; however, further studies are required. Maternal vitamin B12 deficiency has been associated with increased risks of adverse pregnancy outcome, such as miscarriage, neural tube defects, low birth weight, and adverse neurodevelopment. In a woman with a varied diet, the use of additional vitamin supplements in pregnancy would not usually be required; however, where a deficiency state exists, or where vitamin B12 is required in the management of maternal illness or poisoning, treatment should not be withheld.

The use of supplemental vitamin B12 at any stage in pregnancy would not be regarded as medical grounds for termination of pregnancy or any additional fetal monitoring. Where use of high-dose vitamin B12 has been administered as an antidote during pregnancy in maternal poisoning, enhanced antenatal surveillance may be warranted and should be decided on a case-by-case basis. Discussion with UKTIS is recommended in all such cases.

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.