Vegetarianism and veganism are increasingly popular. However, veganism
risks development of vitamin B12 deficiency as it is not available from
plant sources. Moreover, its impact may be slow to be detected because
body stores of vitamin B12 can last years. There is currently no UK
guidance on antenatal diagnosis and management of vitamin B12
deficiency. This paper reviews the metabolism, diagnosis and treatment
of vitamin B12 in pregnancy. It concludes that prophylactic vitamin B12
supplementation should be given to high risk groups around the time of
pregnancy.