Vitamin B12 supplements for pregnancy are essential for women at risk of deficiency, particularly vegans, vegetarians, and those with absorption disorders. This vital nutrient supports fetal neural development, red blood cell formation, and DNA synthesis throughout pregnancy. Whilst most women obtain adequate B12 through a balanced diet, targeted supplementation ensures optimal maternal and fetal health for at-risk groups. Understanding who needs supplementation, appropriate dosages, and safe usage helps support healthy pregnancy outcomes. This guide provides evidence-based information aligned with UK clinical guidance to help you make informed decisions about B12 supplementation during pregnancy.

Why Vitamin B12 Is Essential During Pregnancy

Vitamin B12 (cobalamin) plays a critical role in maternal and fetal health throughout pregnancy. This water-soluble vitamin is essential for DNA synthesis, red blood cell formation, and proper neurological function. During pregnancy, adequate B12 levels support the rapid cell division required for fetal growth and development, particularly in the formation of the neural tube and brain.

The developing fetus relies entirely on maternal B12 stores, which are actively transported across the placenta. Research indicates that low maternal B12 status is associated with a higher risk of adverse outcomes, including neural tube defects, preterm birth, low birth weight and potential impacts on cognitive development, although evidence of direct causation remains limited.

According to UK dietary reference values, adults (including pregnant women) require about 1.5 micrograms of vitamin B12 daily. While most women with balanced diets meet this requirement, supplementation is targeted to those at risk of or with confirmed deficiency.

Vitamin B12 works synergistically with folate (vitamin B9) in cellular processes. Whilst folic acid supplementation is routinely advised before conception and during early pregnancy to prevent neural tube defects, folate can mask the haematological signs of B12 deficiency. When both nutrients are deficient, B12 should be initiated before or alongside folate to avoid worsening neurological symptoms.

If you experience symptoms such as unusual tingling or numbness in hands or feet, difficulty walking, visual disturbances, or severe fatigue during pregnancy, seek prompt medical assessment as these may indicate B12 deficiency requiring treatment. Women with confirmed or suspected B12 deficiency should discuss appropriate supplementation with their GP or midwife to support optimal outcomes for both mother and baby.

Who Needs Vitamin B12 Supplements in Pregnancy

Whilst many pregnant women obtain sufficient vitamin B12 through a balanced diet, certain groups are at significantly higher risk of deficiency and may require supplementation. Vegetarians and vegans represent the highest-risk category, as B12 is naturally found almost exclusively in animal-derived foods. The NHS recommends that vegans and many vegetarians should take a B12 supplement preconception, during pregnancy and whilst breastfeeding.

Women with pernicious anaemia, an autoimmune condition affecting B12 absorption, require ongoing B12 replacement therapy throughout pregnancy. This condition results from a lack of intrinsic factor, a protein necessary for B12 absorption in the terminal ileum. Similarly, individuals who have undergone gastrointestinal surgery—particularly gastric bypass, gastrectomy, or ileal resection—often have impaired B12 absorption and require supplementation.

Certain medical conditions increase the risk of B12 deficiency, including Crohn's disease, coeliac disease, and other malabsorption disorders. Women taking long-term medications such as metformin (for diabetes or polycystic ovary syndrome) or proton pump inhibitors (for acid reflux) may also have reduced B12 absorption. The MHRA advises monitoring B12 levels in patients on long-term metformin treatment.

Women from South Asian backgrounds show higher rates of B12 deficiency in UK populations and may benefit from assessment.

If you fall into any of these risk categories, discuss B12 testing with your GP or midwife early in pregnancy. Initial investigations typically include a full blood count (including MCV), serum B12 and folate levels. If results are borderline or unclear, additional tests such as holotranscobalamin or methylmalonic acid may be helpful. For suspected pernicious anaemia, testing for intrinsic factor antibodies and parietal cell antibodies is appropriate.

Urgent specialist referral is needed if you develop neurological symptoms. Referral is also appropriate for severe anaemia, malabsorption disorders, or when the cause of deficiency remains unclear.

Recommended Dosage and Types of Vitamin B12 Supplements

The UK Reference Nutrient Intake (RNI) for vitamin B12 is 1.5 micrograms per day for adults, including during pregnancy. However, supplementation doses are typically higher than this baseline requirement, particularly for those with deficiency or absorption difficulties.

For pregnant women with dietary deficiency (such as vegans or vegetarians), oral cyanocobalamin at 50-150 micrograms daily is typically recommended, in line with British National Formulary (BNF) guidance. Standard prenatal multivitamins in the UK generally contain between 2.5 and 10 micrograms of B12, which may be sufficient for women with adequate dietary intake but insufficient for those with established deficiency or malabsorption.

Types of vitamin B12 supplements available in the UK include:

• Cyanocobalamin: The most common and cost-effective form, widely available in over-the-counter supplements. It requires conversion to active forms in the body but is stable and well-studied.

• Methylcobalamin: An active form that doesn't require conversion, though evidence for superiority over cyanocobalamin in UK clinical practice is limited.

• Hydroxocobalamin: Commonly used in injectable preparations in the UK and retained longer in the body than cyanocobalamin.

• Adenosylcobalamin: Another active form, though less commonly available in UK supplements.

For women with confirmed B12 deficiency due to malabsorption or pernicious anaemia, intramuscular hydroxocobalamin is the first-line treatment in the UK. The standard regimen is 1mg injections three times weekly for two weeks, followed by maintenance doses of 1mg every 2-3 months. If neurological symptoms are present, treatment may involve 1mg injections on alternate days until no further improvement is seen, followed by maintenance therapy.

When B12 and folate deficiency coexist, B12 replacement should be started before or alongside folic acid (typically 5mg daily) to avoid worsening neurological symptoms.

Monitoring typically includes clinical response assessment and follow-up blood tests. Your healthcare provider will determine the appropriate dose and formulation based on your B12 levels, underlying conditions, and absorption capacity. Always inform your GP or midwife about all supplements you're taking to avoid potential interactions.

Food Sources of Vitamin B12 for Pregnant Women

Obtaining vitamin B12 through dietary sources is the preferred approach for pregnant women without absorption difficulties. Animal-derived foods provide the most reliable and bioavailable sources of this essential nutrient. Understanding which foods are richest in B12 can help pregnant women meet their requirements naturally.

Excellent sources of vitamin B12 include:

• Meat and poultry: Beef, lamb, and chicken provide moderate amounts (2–3 micrograms per 100g serving). The NHS advises pregnant women to avoid liver and liver products entirely due to their high vitamin A content, which may harm the developing baby.

• Fish and seafood: Salmon, trout, tuna, and sardines are excellent sources, providing 3–5 micrograms per serving. UK pregnancy guidance advises limiting tuna to two steaks or four medium-sized cans per week, avoiding shark, swordfish and marlin completely, and limiting oily fish to two portions weekly. Ensure all shellfish is thoroughly cooked and avoid raw shellfish due to infection risk.

• Dairy products: Milk, cheese, and yoghurt provide readily absorbed B12. A 200ml glass of milk contains approximately 1 microgram, whilst cheese and yoghurt provide 0.5–1.5 micrograms per serving.

• Eggs: One large egg provides approximately 0.6 micrograms of B12, primarily in the yolk. British Lion stamped eggs (with the red lion logo) can be eaten runny or raw in pregnancy. Other eggs should be thoroughly cooked until both white and yolk are solid.

For vegetarians and vegans, obtaining adequate B12 from diet alone is challenging. Fortified foods provide some B12:

• Fortified plant-based milk alternatives (soya, almond, oat) typically provide 0.4–1 microgram per serving

• Fortified breakfast cereals may contain 25–100% of the reference intake per serving

• Fortified nutritional yeast provides variable amounts depending on the brand

• Fortified meat alternatives and plant-based products increasingly include added B12

The NHS advises that vegans should take a B12 supplement during pregnancy, as fortified foods may not reliably meet increased needs. Always check product labels, as fortification levels vary considerably between brands. Combining B12-rich foods throughout the day helps maintain steady levels and supports optimal absorption.

Safety and Side Effects of B12 Supplements in Pregnancy

Vitamin B12 supplementation is generally considered safe during pregnancy, with a good safety profile established through extensive clinical use. As a water-soluble vitamin, excess B12 is typically excreted in urine rather than stored. No Tolerable Upper Level has been set for B12 in the UK due to its low toxicity, though serious adverse reactions, while rare, are possible.

According to UK product information for licensed B12 preparations, both oral and injectable forms have been used extensively in pregnant women without evidence of harm to the developing fetus when used at recommended doses.

Side effects from B12 supplementation are uncommon but may include:

• Mild gastrointestinal symptoms such as nausea or diarrhoea, typically with very high oral doses

• Headache or dizziness in some individuals

• Skin reactions (rash, itching) at injection sites when using intramuscular preparations

• Rare but serious allergic reactions, including anaphylaxis with injectable forms

• Hypokalaemia (low potassium) may occur during rapid correction of severe megaloblastic anaemia

If you experience symptoms of a severe allergic reaction (difficulty breathing, severe rash, swelling of face or throat) after taking B12, seek immediate medical attention. When treating severe deficiency, healthcare providers may monitor potassium levels to prevent complications.

Important safety considerations include ensuring supplements are purchased from reputable sources, as quality and purity can vary between manufacturers. Look for products meeting UK or European quality standards. Additionally, inform your healthcare provider about all supplements you're taking.

Whilst B12 supplementation is safe, it should not replace a balanced diet or routine antenatal care. If you have confirmed B12 deficiency, regular monitoring through blood tests ensures treatment effectiveness. Women with pernicious anaemia or other absorption disorders require ongoing specialist input throughout pregnancy.

If you suspect you've experienced a side effect from a vitamin B12 supplement, you can report it through the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk). Never self-diagnose or self-treat suspected deficiency—always seek professional medical advice to ensure appropriate investigation and management tailored to your individual circumstances.

Frequently Asked Questions