Can Cobalamins Be Used to Treat Low Vitamin B12 Levels in Pregnancy?
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Medicines Q&As
Q&A 388.1c Can cobalamins be used to treat low vitamin B12 levels in pregnancy?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals Before using this Q&A, read the disclaimer at www.ukmi.nhs.uk/activities/medicinesQAs/default.asp Published: November 2011
Background
Vitamin B12, a water-soluble B complex vitamin, is essential for red blood cell production 1. Lack of vitamin B12 can cause megaloblastic anaemia 2. Hydroxocobalamin and cyanocobalamin are naturally occurring analogues of vitamin B12 used in the treatment and prophylaxis of megaloblastic anaemia 3.
Vitamin B12 concentrations in the maternal serum fall, from around 205-1025 microgram/L to 50-510 microgram/L, but there is no reduction in the vitamin B12 stored in the mother's liver (about 3000 micrograms)4;5. The fall in vitamin B12 serum concentration is due to several factors: The normal daily requirement increases from 2 micrograms to 3 micrograms in pregnancy 4. Levels can be falsely low because of the increased plasma volume of pregnancy (rather than actual vitamin B12 deficiency) and this may become more pronounced during the latter stages 6.
These factors can make it difficult to diagnose true vitamin B12 deficiency in pregnancy. Long-standing vitamin B12 deficiency can cause megaloblastic anaemia in the mother and may cause neural tube defects or other developmental problems in the infant 1;5;7;8. True vitamin B12 deficiency needs to be treated 4.
Answer The increased daily requirement of vitamin B12 could be met by a diet which contains animal products, but strict vegans may have an insufficient intake of vitamin B12 5. Dietary supplementation with vitamin B12 is not normally required in pregnancy, but if a true deficiency is seen, then it should be treated 3;4. Although not recommended by the manufacturer9, hydroxocobalamin injections can be started or continued during pregnancy1;3;4 10.
There are no epidemiological studies of the use of vitamin B12 during pregnancy3. Data supporting the use of vitamin B12 during pregnancy are limited to case reports in pregnant women who have methylmalonic acidemia, an autosomal recessive disorder diagnosed at birth which is treated with vitamin B12 in responsive patients 11.
A patient diagnosed with methylmalonic acidemia at 4 years of age was treated with 1mg hydroxocobalamin every 4 weeks, which was increased to every 2 weeks at the age of 16. Shortly afterwards she became pregnant, and hydroxocobalamin 1mg every 2 weeks was continued throughout pregnancy. A healthy baby was born by caesarean section at 36 weeks gestation 12. A second patient with methylmalonic acidema was treated with hydroxocobalamin 5mg/week from the 12th week of pregnancy. A healthy baby was born at 38 weeks gestation, by caesarean section. The baby was followed up over 2 years and showed normal development 13.
Intramuscular hydroxocobalamin has replaced oral cyanocobalamin as the form of vitamin B12 of choice for therapy. Oral cyanocobalamin can only be prescribed on the NHS for treating or preventing vitamin B12 deficiency in a patient who is a vegan or who has a proven vitamin B12 deficiency of dietary origin 2. Hydroxocobalamin is retained in the body longer than cyanocobalamin, allowing for 3- monthly maintenance dosing 3;13.
From the NHS Evidence website www.evidence.nhs.uk 1
Medicines Q&As
Summary
Vitamin B12 can be used during pregnancy provided that the anaemia is caused by vitamin B12 deficiency. Intramuscular hydroxocobalamin is the preferred treatment choice; oral cyanocobalamin is not prescribable on the NHS unless it is to treat or prevent vitamin B12 deficiency in a patient who is a vegan or who has a proven vitamin B12 deficiency of dietary origin. The use of vitamin B12 at any stage in pregnancy would not usually be regarded as grounds for additional foetal monitoring.
Limitations No controlled human studies have been carried out. The above outline is presented for guidance. In general, prescribing in pregnancy should be considered on an individual basis, particularly if there are unusual circumstances (e.g. complicated obstetric history, requirement for high doses etc). In these instances, further advice can be sought from your local (or Regional) medicines information service.
References
Quality Assurance
Prepared by Ranu Ali, Pharmacist, London Medicines Information Service (Northwick Park Hospital)
Date Prepared 15/11/11
Checked by Alexandra Denby, Pharmacist, London Medicines Information Service (Northwick Park Hospital)
Email contact [email protected]
Date of check 01/12/11
Search strategy
EMBASE; HYDROXOCOBALAMIN AND PREGNANCY/. EMBASE: HYDROXOCOBALAMIN AND FIRST TRIMESTER PREGNANCY/ OR SECOND TRIMESTER PREGNANCY/ OR THIRD TRIMESTER PREGNANCY/; Medline: HYDROXOCOBALAMIN/; AND PREGNANCY/; In-house past enquiries: 95096, 94431, 94465, 92558, 92056, 91904, 91138, 88253, 87047
From the NHS Evidence website www.evidence.nhs.uk 2