Are vitamin B12 injections safe during pregnancy?

From the Guidelines

Vitamin B12 injections are safe during pregnancy and are often recommended for pregnant women with B12 deficiency to ensure adequate levels for fetal development. The typical dosage for B12 deficiency during pregnancy is 1,000 mcg of cyanocobalamin or hydroxocobalamin given intramuscularly, with frequency depending on severity (daily or weekly initially, then monthly for maintenance) 1. According to the guidelines for pregnancy after bariatric surgery, postsurgery vitamin B12 regimens should be continued preconception at a dose of 1 mg every 3 months via intramuscular depot injection 1.

Key Considerations

• Vitamin B12 deficiency can lead to anemia, fatigue, and neurological issues in the mother, and developmental problems in the baby 1.
• Pregnant women with conditions affecting absorption, such as pernicious anemia, Crohn's disease, or after gastric bypass surgery, may require B12 injections 1.
• Oral supplements are an alternative for mild deficiency, but injections provide more reliable absorption for those with severe deficiency or absorption issues 1.
• The British Obesity and Metabolic Surgery Society guidelines recommend measuring vitamin B12 levels during the preconception period before additional folic acid supplements are given 1.

Monitoring and Supplementation

• Serum levels of vitamin B12 should be checked at least once per trimester and use pregnancy-specific ranges 1.
• Additional vitamin B12 supplementation should be given as needed to maintain serum concentrations within normal limits 1.
• A multivitamin and mineral supplement should be taken daily prior to conception and throughout pregnancy, containing the following at a minimum: copper, zinc, selenium, folic acid, iron, thiamine, vitamin E, and beta-carotene (vitamin A) 1.

From the FDA Drug Label

Pregnancy Teratogenic Effects: Pregnancy Category C Adequate and well-controlled studies have not been done in pregnant women However, vitamin B12 is an essential vitamin and requirements are increased during pregnancy. Amounts of vitamin B12 that are recommended by the Food and Nutrition Board, National Academy of Science-National Research Council for pregnant women (4 mcg daily) should be consumed during pregnancy.

The use of Cyanocobalamin (IM) in pregnancy is classified as Pregnancy Category C, indicating that adequate and well-controlled studies have not been done in pregnant women. However, vitamin B12 is an essential vitamin and its requirements are increased during pregnancy. The recommended daily amount for pregnant women is 4 mcg daily.

• The FDA label does not provide direct evidence of the safety of B12 injections in pregnancy, but it does indicate that vitamin B12 is essential and requirements are increased during pregnancy 2. Given the lack of direct evidence, a conservative clinical decision would be to use B12 injections in pregnancy only if necessary and under close medical supervision.

From the Research

Vitamin B12 Injections in Pregnancy

• The safety of vitamin B12 injections in pregnancy is not directly addressed in the provided studies, but we can look at the available information on vitamin B12 supplementation during pregnancy.
• A study published in 2024 3 found that oral vitamin B12 supplementation during pregnancy may reduce the risk of maternal vitamin B12 deficiency and improve maternal vitamin B12 concentrations, but the evidence is very uncertain.
• The same study 3 found that vitamin B12 supplementation during pregnancy may improve infant vitamin B12 status, but the potential impact on longer-term clinical and functional maternal and child health outcomes has not yet been established.
• Another study published in 2017 4 found that oral administration of high-dose vitamin B12 is as effective as intramuscular administration for correcting anemia and neurologic symptoms, but intramuscular therapy leads to more rapid improvement and should be considered in patients with severe deficiency or severe neurologic symptoms.
• There is no direct evidence on the safety of vitamin B12 injections in pregnancy, but it can be inferred that vitamin B12 supplementation, in general, is considered safe during pregnancy, and the choice between oral and intramuscular administration depends on the individual case.

Potential Benefits and Risks

• The potential benefits of vitamin B12 supplementation during pregnancy include reducing the risk of maternal vitamin B12 deficiency and improving maternal and infant vitamin B12 status 3.
• The potential risks of vitamin B12 supplementation during pregnancy are not well established, but it is generally considered safe 4.
• A study published in 2017 5 found that subclinical vitamin B12 deficiency affects between 2.5% and 26% of the general population, and deficiency can affect individuals at all ages, but most particularly elderly individuals, infants, children, adolescents, and women of reproductive age.
• Another study published in 2019 6 found that cobalamin deficiency most significantly affects functions of blood, nervous system, and inflammatory response, and can cause various neurological manifestations, including subacute combined degeneration of spinal cord, sensomotor polyneuropathy, optic nerve neuropathy, and cognitive disorders.