What do medical sources say about Vitamin B12 during pregnancy?

1st Trimester: MotherToBaby says the recommended daily amount of B12 in pregnancy, 2.6 micrograms from food and supplements, is not expected to increase miscarriage or birth-defect risk. This does not show that supplements prevent either outcome: Cochrane could not analyze miscarriage results and found no trials measuring neural tube defects. Some studies link low B12 status with miscarriage or neural tube defects, but other findings differ and do not show that low B12 caused an outcome. ACOG says vegetarians should take a supplement, NICE says people on restricted diets may need B12-rich foods or a supplement, and NHS Specialist Pharmacy Service says B vitamins other than folic acid are not needed unless a deficiency is known. Ask your provider about your situation. 2nd Trimester: MotherToBaby says the recommended daily amount, 2.6 micrograms from food and supplements, is not expected to increase birth-defect, preterm-birth, or low-birth-weight risk. Studies of low B12 status have linked deficiency with low birth weight, while the preterm-birth estimate was uncertain; these studies do not show that supplements prevent either outcome. Cochrane found uncertain effects of supplements on preterm birth and low birth weight, and no trials measuring neural tube defects. ACOG and NICE describe possible supplement use for vegetarian or restricted diets, while NHS Specialist Pharmacy Service says B vitamins other than folic acid are not needed unless a deficiency is known; no separate second-trimester B12 recommendation was identified. Ask your provider about your situation. 3rd Trimester: MotherToBaby says the recommended daily amount, 2.6 micrograms from food and supplements, is not expected to increase birth-defect, preterm-birth, or low-birth-weight risk. Observational studies link low B12 status with some pregnancy outcomes, but they do not establish cause or show that supplements prevent those outcomes. Cochrane found no neural tube defect trials and uncertain supplement effects on preterm birth and low birth weight. A Nepal trial and a later analysis reported mixed infant development results at 50 micrograms per day, well above the pregnancy RDA; these findings do not establish an effect of ordinary dietary intake. No separate third-trimester B12 recommendation was identified. Ask your provider about your situation.

What do medical sources say about Vitamin B12 while breastfeeding?

LactMed says B12 is a normal part of human milk, and the recommended daily amount while breastfeeding is 2.8 micrograms from food and supplements. If a parent is deficient, an exclusively breastfed infant can also become deficient; reports describe anemia, weak muscle tone, movement changes, and changes in skin or hair. Many infant reports involve families already diagnosed or referred for deficiency, so they cannot estimate how often this occurs in all breastfed infants. LactMed says higher doses may be used to correct maternal deficiency, and NIH ODS says no upper limit has been set; this does not show that extra B12 improves outcomes for people without deficiency. Ask your provider about your situation.

Where do sources disagree on Vitamin B12 in pregnancy or breastfeeding?

Whether a restricted or vegetarian diet calls for routine B12 supplementation during pregnancy ACOG's pregnancy nutrition table lists 2.6 micrograms of B12 and says vegetarians should take a supplement. NICE says people following a restricted diet may need B12-rich foods or a B12 supplement. NHS Specialist Pharmacy Service says B vitamins other than folic acid are not needed during pregnancy unless a deficiency is known. The sources emphasize different thresholds: dietary risk and meeting nutrient needs versus treatment when deficiency is known. This is a difference in supplementation guidance, not evidence that normal B12 intake causes pregnancy harm. The pregnancy rating remains compatible for recommended total intake. Dietary pattern and known deficiency matter to the guidance, but the evidence does not show that routine RDA intake causes harm or that supplements prevent miscarriage or neural tube defects.

Back to search

Vitamin B12

Vitamin & mineral

Also called · 6 names▾

cobalamin, cyanocobalamin, methylcobalamin, hydroxocobalamin, Vitamin B-12, B12

Vitamin supplement

Herbs and supplements are not FDA-approved before sale. About these sources

Capsule/tablet

Pregnancy

Recommended intake and deficiency-treatment doses are different questions. MotherToBaby says taking the RDA is not expected to increase the chance of miscarriage, birth defects, preterm delivery, or low birth weight. The pregnancy RDA is 2.6 mcg per day from all food and supplement sources; the lactation RDA is 2.8 mcg. No upper limit has been established, but that is not evidence that larger routine amounts improve outcomes. Miscarriage: MotherToBaby describes studies linking low blood B12 with miscarriage, while noting other factors may explain the link. Bala et al. (2021) measured B12 and homocysteine in 83 first-trimester early-pregnancy-loss cases and 70 healthy pregnant controls and also meta-analyzed prior studies; its association does not establish that low B12 caused pregnancy loss. Dogan and Sahin (2024) compared 93 miscarriage cases with 93 controls; B12 levels were lower in cases, but regression identified homocysteine, not B12, as a predictor. The Cochrane review included five trials with 984 pregnant women; two trials reported miscarriage but lacked quantitative results for analysis and did not clearly define miscarriage. Birth defects and neural tube defects: MotherToBaby says RDA intake is not expected to increase birth-defect risk, but whether deficiency increases that risk is not known. Molloy et al. (2009) measured maternal blood at an average of 15 weeks in three Irish nested case-control groups; the lowest B12 quartiles had two- to threefold higher adjusted odds of an NTD-affected pregnancy than the highest quartiles. That observational finding concerns status, not supplement treatment or prevention. Nie et al. (2025) reviewed 38 studies including 2,316 NTD cases and 4,298 controls and found lower B12 concentrations in the NTD group (SMD -0.23, 95% CI -0.32 to -0.14; I2 58.3%). Although its conclusion discusses supplementation, the pooled data compare blood concentrations and do not show that supplements prevent NTDs. Cochrane found no trials evaluating supplementation effects on NTDs. Preterm birth and low birth weight: Rogne et al. (2017) identified 22 eligible studies with 11,993 observations and meta-analyzed 18 studies with 11,216 observations. Deficiency below 148 pmol/L was associated with low birth weight (adjusted RR 1.15, 95% CI 1.01 to 1.31). For preterm birth, the deficiency estimate was RR 1.21 (95% CI 0.99 to 1.49), so its confidence interval includes no difference. Cochrane found uncertain supplement effects on preterm birth (RR 0.97, 95% CI 0.55 to 1.74; 2 trials, 340 women) and low birth weight (RR 1.50, 95% CI 0.93 to 2.43; 2 trials, 344 women). Child development: In the 2023 Nepal placebo-controlled trial, 800 pregnant women received 50 mcg B12 daily or placebo from early pregnancy through six months postpartum; 71% had low or marginal baseline status. Supplementation improved B12 status but did not improve the primary infant growth or cognitive outcomes. A 2026 secondary analysis of 712 infants reported lower motor scores at 8 to 12 weeks in the supplement group; this was a secondary analysis of the same trial, not a separate trial, and the authors reported stronger negative results in some subgroups. MATCOBIND (2026) randomized vegetarian pregnant participants to 250 mcg or 50 mcg daily through six months postpartum; 531 completed the study. The higher-dose group had a higher mental developmental quotient, while motor scores did not differ. These different populations, doses, comparators, outcomes and ages do not answer whether routine RDA-level intake changes child development. Reviews in 2025 and 2026 found a small and mixed evidence base, with many observational studies and few trials.

Breastfeeding

LactMed says B12 is a normal component of human milk and that milk levels correlate with maternal intake and blood levels. It reports the recommended daily intake is 2.8 mcg during lactation and says supplementation may be needed to meet intake or correct a known deficiency; daily amounts of 50 to 250 mcg may be used in maternal deficiency. Those treatment amounts should not be confused with the RDA. LactMed also notes infant B12 status can improve when a deficient parent supplements, while direct infant treatment may be recommended when available. Infant-effects evidence is concentrated in deficient families and selected clinical reports. Halicioglu et al. (2011) described 30 predominantly breastfed infants with nutritional B12 deficiency; all mothers had low serum B12. Wirthensohn et al. (2023) reviewed 102 publications describing 292 clinically diagnosed infant cases; the mean age at first symptoms was four months, and exclusive breastfeeding and maternal B12 status predicted infant biomarkers. These case data describe clinical presentations and cannot estimate incidence among all breastfed infants. Ata and Tas (2025) included 217 breastfed infants aged 9 to 12 months who already had B12 levels at or below 300 pg/mL, so the sample is selected and not representative of all infants. Furlan et al. (2026) studied 240 infants and 238 mothers referred to a regional clinical center after newborn screening; this is also a referral cohort. A 2026 case report described one breastfed infant whose mother had a diet low in animal products; a single case cannot estimate frequency. The evidence supports attention to deficiency status, not a claim that usual B12 intake harms breastfed infants or that extra intake produces a developmental benefit.

Whether a restricted or vegetarian diet calls for routine B12 supplementation during pregnancy

Source A says: ACOG's pregnancy nutrition table lists 2.6 micrograms of B12 and says vegetarians should take a supplement. NICE says people following a restricted diet may need B12-rich foods or a B12 supplement. (ACOG: Healthy Eating During Pregnancy, NICE NG247: Maternal and child nutrition)
Source B says: NHS Specialist Pharmacy Service says B vitamins other than folic acid are not needed during pregnancy unless a deficiency is known. (NHS Specialist Pharmacy Service: Vitamin B12 deficiency treatment during pregnancy)
Why they differ: The sources emphasize different thresholds: dietary risk and meeting nutrient needs versus treatment when deficiency is known. This is a difference in supplementation guidance, not evidence that normal B12 intake causes pregnancy harm.
Other sources: NIH ODS says people who consume few or no animal products are at increased risk of B12 deficiency and may benefit from a supplement; it also says effects of supplementation on other health outcomes are unclear. (NIH Office of Dietary Supplements: Pregnancy Health Professional Fact Sheet)
What the evidence shows overall: The pregnancy rating remains compatible for recommended total intake. Dietary pattern and known deficiency matter to the guidance, but the evidence does not show that routine RDA intake causes harm or that supplements prevent miscarriage or neural tube defects.

Infant development findings after maternal B12 supplementation

Source A says: The Nepal randomized trial found no improvement in its primary infant growth or cognitive outcomes. A 2026 secondary analysis of the same trial reported lower motor scores at 8 to 12 weeks in the supplement group. (Chandyo et al., Lancet 2023: Vitamin B12 supplementation during pregnancy in Nepal, Kvestad et al., Journal of Nutrition 2026: Secondary analysis of early motor performance)
Source B says: MATCOBIND found higher mental developmental scores with 250 mcg than with 50 mcg daily among vegetarian pregnant participants, but no motor-score difference. (Nagpal et al., BMJ Paediatrics Open 2026: MATCOBIND randomized trial)
Why they differ: The studies used different settings, participant diets, doses, comparison groups, outcome tests and ages. The Nepal motor finding was a secondary analysis, while MATCOBIND compared two active doses rather than supplement with no supplement.
Other sources: A 2025 systematic review included 11 studies, four randomized trials and seven observational studies, and called for more research because the clinical-trial evidence is limited. (Bonifácio et al., Current Nutrition Reports 2025: Systematic review of maternal B12 and neurodevelopment)
What the evidence shows overall: These findings are mixed and specific to their study populations and doses. They do not establish a developmental benefit or harm from ordinary dietary intake or the pregnancy RDA.

Last reviewed 2026-10-16

Independent check 2026-10-16

Not yet clinician-reviewed

Ask your provider about your situation.

Vitamin B12

Vitamin B12 — Breastfeeding

What the research shows

What's in it / what was tested

Sources disagree

Options sources describe

Beyond pregnancy

All sources

Related