Vitamin B12 deficiency and pregnancy

Seek expert advice.

• there are no published studies looking into congenital malformations following use of vitamin B12 during pregnancy (1)
  • there is no evidence that treatment with vitamin B12 is associated with an increased risk of congenital malformations or other adverse foetal effects due to in utero exposure
    
    
• there is evidence to suggest that maternal vitamin B12 deficiency increases the risk of neural tube defects in the newborn:
  • a total serum cobalamin level below 148 picomol/L (200 nanograms/L) has been suggested as a threshold to indicate deficiency, but this level alone can be an unreliable indicator of vitamin B12 deficiency in pregnancy (1)
    • because active transport of vitamin B12 to the foetus usually causes total serum vitamin B12 concentrations to fall to around half pre-pregnancy level by 6 months, and total serum vitamin B12 may not reflect active B12 levels or indicate depletion in maternal tissues or liver stores
    • levels of other biochemical markers (for example, holotranscolbalamin (active vitamin B12), homocysteine and methylmalonic acid) and clinical symptoms that suggest deficiency may also need to be considered based on the advice of a haematologist
      
• if vitamin B12 deficiency is diagnosed in pregnancy or during breastfeeding
  • offer an anti-intrinsic factor antibody test if
    • if autoimmune gastritis is suspected and they have not previously had a positive anti-intrinsic factor antibody test at any time or
    • an operation that could affect vitamin B12 absorption (such as total gastrectomy or complete terminal ileal resection)
  • and
    • start treatment with intramuscular vitamin B12 treatment
      
      
• hydroxocobalamin can be used during pregnancy to treat conditions caused by vitamin B12 deficiency including megaloblastic anaemia, pernicious anaemia, and neurological problems
  
  
• There are no specific UK guidelines for the treatment of vitamin B12 deficiency during pregnancy and no specific UK dosing recommendations are available.
  • Prescribers should seek urgent advice from a haematologist on treating vitamin B12 deficiency anaemia in a pregnant woman (2).
  • UK Teratology Information Service (UKTIS) has safety information on the use of vitamin B12 in pregnancy
    
    
• treatment options (3)
  • continue vitamin B12 replacement if treatment was started prior to conception
  • prescribing in pregnancy should be considered on an individual basis, particularly if there are unusual circumstances, such as complicated obstetric history.
  • hydroxocobalamin are naturally occurring analogues of vitamin B12 used in the treatment of vitamin B12 deficiency
    • cyanocobalamin injection should not be prescribed as the NHS considers this formulation less suitable for prescribing
      
• when vitamin B12 deficiency state exists AND vitamin B12 is clinically indicated for management of maternal illness in pregnancy, treat with IM hydroxocobalamin (2).
  • Dosing regimes (2):
    • UK recommendations the treatment of pernicious anaemia and other macrocytic anaemias due to vitamin B12 deficiency in the general population can also be considered for use in pregnancy
    • without neurological involvement
      • intramuscular hydroxocobalamin: 1 mg three times a week for 2 weeks initially, then 1 mg every 2 to 3 months thereafter (if the deficiency is not diet related); or
      • if using oral cyanocobalamin then consider a dose of at least 1mg a day when prescribing during pregnancy (3)
    • with neurological involvment
      • seek urgent advice (3)
        • consider intramuscular hydroxocobalamin if specialist advice is not immediately available. Administer 1mg daily on alternative days until no further improvement, then 1mg every 2 months
          
  • monitoring in pregnancy (3)
    • reassess symptoms 1 month after starting treatment, instead of the usual recommended period of 3 months.
    • use of vitamin B12 at any stage in pregnancy is not regarded as grounds for additional foetal monitoring

A Nepal based study showed that there was no improvement in infant growth or neurodevelopment associated with vitamin B12 supplementation or difference in infant haemoglobin concentrations despite a substantial biomarker response and improved vitamin B12 status among mothers and infants (3)

Reference:

• (1) NHS Specialist Pharmacy Service (June 2020).How should vitamin B12 deficiency in pregnancy be treated?
• (2) NHS Specialist Pharmacy Service (April 2022). Vitamin B12 deficiency: treatment during pregnancy
• (3) NHS Specialist Pharmacy Service (December 2024). Vitamin B12 deficiency: treatment during pregnancy Available from: https://www.sps.nhs.uk/articles/vitamin-b12-deficiency-treatment-during-pregnancy/
• (4) Chandyo RK et al. The effect of vitamin B12 supplementation during pregnancy on infant growth and development in Nepal: a community-based, double-blind, randomised, placebo-controlled trial. Lancet April 6th 2023 https://doi.org/10.1016/S0140-6736(23)00346-X