vitamin B12 deficiency and pregnancy

Last edited 05/2022 and last reviewed 06/2022

Seek expert advice.

  • There are no published studies looking into congenital malformations following use of vitamin B12 during pregnancy.
    • 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
    • although low levels of maternal vitamin B12 are common during pregnancy, in most cases treatment is not necessary
      • clinically significant vitamin B12 deficiency can cause megaloblastic anaemia and/or neurological problems in the mother and neural tube defects in the newborn, and therefore needs to be treated
  • 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.
  • Intramuscular (IM) hydroxocobalamin is the preferred treatment choice for clinical conditions caused by vitamin B12 deficiency, including during pregnancy, and should usually be prescribed according to the current recommendations in the BNF.
  • 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)
      • with neurological involvment
        • intramuscular hydroxocobalamin: 1mg daily on alternate days until no further improvement, then 1mg every 2 months

The use of vitamin B12 at any stage in pregnancy would not usually be regarded as grounds for additional foetal monitoring.

Reference: