Is vitamin B12 safe during pregnancy?

What does the evidence say about vitamin B12 during pregnancy?

1. The RDA for vitamin B12 during pregnancy is 2.6 mcg a day, and taking this amount is not expected to increase the chance of birth defects. 1
2. If a breastfeeding parent is B12-deficient, an exclusively breastfed infant has an increased chance of becoming deficient too, with possible low muscle tone, tremors, anemia, and changes in skin and hair development. 1
3. There is currently no tolerable upper intake level set for vitamin B12 because it isn't stored in the body in excess amounts, though some studies have associated B12 deficiency with preterm delivery. 2
4. Pregnancy- and infancy-specific reference ranges should be used when checking B12 status, since requirements rise to 2.6 mcg a day in pregnancy and 2.8 mcg a day during lactation, and a marker called holotranscobalamin offers a diagnostic advantage over standard serum B12 testing in pregnancy. 3
5. Following a vegetarian diet, or one low in animal-source foods, is a key risk factor for B12 deficiency, and maternal deficiency has been linked in observational studies to birth defects, growth restriction, preterm delivery, and poorer infant memory, language, and motor development, though randomized trial evidence on supplementation's effect on those outcomes is still limited. 4

Is vitamin B12 safe in each trimester?

• First trimester. B12 works alongside folate in early neural tube development. Data on typical RDA-level intake hasn't shown an increased chance of birth defects, but deficiency itself has been linked to neural tube defects in some studies.
• Second trimester. Needs stay at 2.6 mcg a day through pregnancy. If you're vegan, vegetarian, or eat little animal food, this is a good point to confirm your prenatal covers B12 adequately or ask about a separate supplement, since deficiency is a well-documented risk in that group.
• Third trimester. Some research associates low B12 status with preterm delivery. Ongoing maternal deficiency can also affect a breastfed infant's B12 status after birth, since the recommended intake rises slightly to 2.8 mcg a day once you're breastfeeding.