Vitamin B12 Before Pregnancy for Vegetarians and Vegans

What does the evidence say about vitamin B12 during pregnancy?

1. Vitamin B12 only occurs naturally in foods that come from animals, so pregnant vegetarians and vegans are advised to prioritize B12-fortified foods and, if needed, a supplement to meet the 2.6 microgram daily amount recommended in pregnancy. 1
2. B12 deficiency in pregnancy has been linked to infant birth defects, growth restriction, and preterm delivery, and a vegetarian diet is a key risk factor for developing that deficiency in the first place. 2
3. Because vitamin B12 is essential for the developing nervous system, maternal deficiency during pregnancy and breastfeeding can lead to delayed brain myelination and other neurological effects in an infant that are described as severe and not always fully reversible. 3
4. For pregnant or breastfeeding vegan women, one workable approach is a single daily dose of 50 micrograms of B12, split doses of 2 micrograms taken three times a day, or a larger 1,000 microgram dose taken twice a week, using an individual B12 supplement rather than relying on a multivitamin alone. 4
5. A large-scale supplementation trial found infants of vegetarian mothers who took a higher daily B12 dose throughout pregnancy and into the postpartum period had better neurodevelopmental scores at 9 to 12 months than infants of mothers on a lower maintenance dose, underscoring that adequate B12 status is worth confirming well before delivery. 2

Is vitamin B12 safe in each trimester?

• First trimester. If you're vegetarian or vegan and pregnancy is still a few months off, this is the ideal time to get your B12 status checked and start a reliable daily source. B12 stores in the body are typically built up over months, not days, so starting early means you're not making up ground once you conceive.
• Second trimester. As you get closer to conceiving, keep your B12 intake consistent. The nervous system begins forming very early, and maternal B12 status in those first weeks matters for that development, so this isn't a nutrient to start addressing only after a positive test.
• Third trimester. Once you're pregnant, needs rise slightly, and the amount in a standard prenatal multivitamin may not be enough for a fully plant-based diet. Many vegan and vegetarian pregnancy nutrition guides recommend an individual B12 supplement on top of a prenatal, since bioavailability improves when it's taken separately.