B12 During Pregnancy

Vitamin B12 is essential during pregnancy as it is required for one‑carbon metabolism, DNA synthesis, erythropoiesis, myelination, and epigenetic programming. These processes occur during a period of rapid maternal tissue expansion, placental growth, and fetal neurodevelopment. Low B12 status is consistently associated with adverse outcomes in both mother and baby.¹

• Methylation in pregnancy
  Vitamin B12 is an essential cofactor for methionine synthase and methylmalonyl‑CoA mutase, required for the remethylation of homocysteine to methionine, and subsequently S‑adenosylmethionine (SAMe). During pregnancy, these processes are central to nucleotide synthesis (cell division in the placenta and fetus), DNA and histone methylation (epigenetic programming), and hematopoiesis.²
  
  
• Homocysteine regulation
  Elevated homocysteine and methylmalonic acid (MMA) are biochemical hallmarks of B12 deficiency. Homocysteine promotes oxidative stress and can impair reproductive and early developmental outcomes.³
  
  
• Maternal health
  Pregnancy increases the body’s demands for B12 due to increased blood volume, placental transfer of B12 to the fetus, and preparation for breastfeeding.⁴
  Vitamin B12 deficiency is one of the most common causes of anemia, along with iron deficiency.⁵
  
  
• Fetal development
  SAMe is required for methylation reactions involved in neurogenesis, myelination, and synaptic plasticity in the developing fetal brain. Adequate maternal B12 concentrations (312–408 pg/mL) in the first trimester are associated with significantly higher neonatal motor skills, receptive language, and cognitive scores at 40 days, compared with <312 pg/mL.⁶ Insufficient vitamin B12 in pregnancy can impair synthesis of S-adenosylmethionine (SAMe), which can then impact both the developing brain and neural tube closure. Low B12 may also cause elevated homocysteine levels, which have embryotoxic effects and cause damage to endothelial and smooth muscle cells.⁷
  
  
• Folate metabolism
  B12 is essential for maintaining normal folate metabolism. Lack of B12 causes folate to become ‘trapped’ in the 5-methyl-THF form, and also leads to a deficiency of methionine. This impairs proper DNA synthesis and other processes within rapidly dividing placental and fetal tissues.⁸

The Recommended Dietary Allowance (RDA) for vitamin B12 during pregnancy is 2.6-2.8 micrograms per day.

B12 overdose is unlikely because it is a water-soluble vitamin, and excess is flushed out in urine. There is no Tolerable Upper Intake Level established for B12 in the general population due its very low toxicity.⁹

Clinical trials involving pregnant women typically use much higher dosages of B12 (e.g. 5-250 µg/day), but these are therapeutic dosages given under medical supervision. Women considering higher dosages during pregnancy should discuss this with a health professional.

The best way to get B12 during pregnancy depends on your own health needs and current B12 levels.

Women with B12 deficiency due to impaired absorption, genetic conditions, and/or dietary restrictions may need high-dose B12 supplementation in the form of B12 injections or sublingual tablets.

• B12 injections
  Intramuscular B12 injections are safe during pregnancy and may be recommended for pregnant women with B12 deficiency to restore adequate levels for fetal development. The typical dosage is 1,000 mcg of cyanocobalamin or hydroxocobalamin given intramuscularly, with frequency depending on the severity of the deficiency (daily or weekly initially, then monthly for maintenance).
  
  
• Sublingual B12
  A large 2019 study found that sublingual B12 supplementation was significantly more effective in improving serum B12 than injections.¹⁰ Although this study did not include pregnant women, the authors noted that the sublingual method overcomes the challenges of IM injections and should be the first line option for patients with B12 deficiency.
  A 2020 study found that oral vitamin B12 per day was as safe and effective as sublingual or intramuscular supplementation.¹¹
  
  
• Cyanocobalamin is the synthetic form of B12. It contains a cyanide molecule which must be removed and metabolized by the body. Researchers advise against long-term supplementation to avoid accumulation in the body. Hydroxocobalamin and methylcobalamin do not contain cyanide.¹²

A nutritious diet with plenty of fresh fruits, vegetables, lean protein, and healthy fats is recommended at all stages of pregnancy. Many of these foods are also rich in B1, but specific foods that are ideal for pregnancy include:

• Cooked fish and shellfish
  Low-mercury seafood such as salmon, trout, tuna, oysters, and clams are safe during pregnancy and provide some of the highest amounts of natural B12. Clams and oysters are an especially rich source of vitamins and minerals.
  Note: Avoid fish and shellfish that are raw or smoked, or high in mercury, such as swordfish, marlin, or shark.
  
  
• Lean meat
  Beef, lamb, pork, and poultry (chicken, turkey) are excellent sources of B12.
  
  
• Eggs and dairy
  Pasteurized milk, unsweetened yogurt, and eggs are consistently listed as good B12 sources. Hard cheeses such as cheddar and parmesan are safe.
  Note: avoid unpasteurized (raw) milk products or soft cheeses as they can contain Listeria bacteria which may be harmful in pregnancy.
  
  
• Fortified foods and beverages
  Many breads, cereals, juices, snacks, and plant milks are fortified with vitamins and minerals, including B12. These can be helpful for people who choose not to eat animal products.
  Note: fortified foods may not be suitable for women with MTHFR genetic mutations as they cannot properly metabolize the folic acid these foods contain.
  
  
• Nutritional yeast
  Nutritional yeast is safe during pregnancy and contains a small amount of B12, which may be suitable for women who are pregnant and vegetarian/vegan.

US pregnancy guidelines do not typically recommend routine B12 supplementation for all pregnant women, but they do encourage adequate intake through diet or prenatal vitamins to avoid deficiency. It’s important to note that mild B12 deficiency is common during pregnancy, especially in the third trimester, with some research showing that up to 38% of women may have low levels by delivery.¹³

Many prenatal vitamins contain Vitamin B12. B12 is often poorly absorbed due to dietary insufficiency, impaired gastrointestinal absorption, and genetic factors that affect how the body processes some forms of the nutrient, particularly synthetic B12 (cyanocobalamin).

Look for a pregnancy multivitamin (prenatal) that contains B12 in the form of methylcobalamin, which is the natural, bioidentical form of B12 immediately available for use in the body upon ingestion. Research has suggested the three natural forms of B12 (methylcobalamin, adenosylcobalamin, and hydroxycobalamin) may be superior in bioavailability and safety.¹⁴