Is vitamin B12 important during pregnancy?

Yes as a nutrient, and the proof that a supplement helps the baby is missing. According to EFSA, pregnant women need an adequate intake of 4.5 micrograms a day, against 4 for other adults, to cover what the fetus stores. A 2024 Cochrane review of five trials in 984 women found supplements cut maternal B12 deficiency from 67.9 to 25.9 percent, on very low-certainty evidence. The same review could not show any effect on anemia, preterm birth or low birth weight. The women who most need B12 are those who eat no animal products.

Unsettled. The open question is about the baby, and it is open because the trials are small. Preterm birth and low birth weight were each measured in two trials of about 340 women, and the intervals run from a clear benefit to a clear harm. No trial has tested whether B12 prevents neural tube defects. That is a gap in the research, which is different from evidence that B12 does nothing.

What the trials found

Mothers' blood levels

The Cochrane review pooled trials from India, Bangladesh, South Africa and Croatia, with doses of 5 to 250 micrograms a day started between 8 and 28 weeks of pregnancy. Supplements cut deficiency with a risk ratio of 0.38 (95% CI 0.28 to 0.51) in 2 trials of 272 women. That is a blood marker. It is not a clinical outcome. A 2025 meta-analysis of supplement trials in low- and middle-income countries found the same direction: maternal B12 rose (standardized difference 0.39, 95% CI 0.11 to 0.68) and the odds of deficiency fell (OR 0.43, 95% CI 0.19 to 0.95). B12 in breast milk rose too, most clearly when the supplement was given after birth, and the authors found no consistent effect on B12 in the baby's or the cord blood.

The baby

Against no supplement, the risk ratio for preterm birth was 0.97 (95% CI 0.55 to 1.74) and for low birth weight 1.50 (95% CI 0.93 to 2.43), both on low-certainty evidence. Anemia in the mothers was 70.9 percent with B12 and 65.0 percent without (RR 1.08, 95% CI 0.93 to 1.26). The women in the main trial were all taking iron and folic acid as well.

The trial described in most detail randomized 366 pregnant women in Bangalore, India, to 50 micrograms a day from before 14 weeks until 6 weeks after birth, or placebo. Their median plasma B12 was 216 pmol/L against 111 on placebo in the second trimester and 184 against 105 in the third. Fewer babies were growth-restricted in the B12 group, 33 of 131 (25 percent) against 43 of 125 (34 percent), and the difference did not reach significance (P = 0.11). At 9 months, development scores did not differ in the 178 infants tested, about half of those born. At 30 months, the 218 children whose mothers took B12 scored higher on expressive language (β = 0.14, P = 0.03). Several areas were tested and the abstract states no correction for that, so the reviewers rated this low certainty.

The trials are also recent. A 2012 systematic review of vitamin trials in pregnancy found none that had tested B12 before or during pregnancy at all.

What observational data link to low B12

These studies compare women with more and less B12 and cannot show that B12 is the cause. Across 18 cohorts with individual data on 11,216 women, deficiency below 148 pmol/L went with a higher risk of low birth weight (adjusted risk ratio 1.15, 95% CI 1.01 to 1.31), with no straight-line link to birth weight. Ten studies in 10,595 women tie deficiency to gestational diabetes (OR 1.46, 95% CI 1.21 to 1.79), while an earlier dose-response analysis found no significant link. Across 38 studies, mostly case-control with blood often drawn after the outcome, mothers of babies with neural tube defects had slightly lower B12 (standardized difference -0.23, 95% CI -0.32 to -0.14). Women with preeclampsia had slightly lower B12 too (-15.24 pg/mL, 95% CI -27.52 to -2.954), with results so inconsistent between studies (I² 97.8%) that the number says little. None of these four figures comes with an absolute risk.

Who should be careful

Not for everyone. If you eat no animal products, B12 matters more for you than for anyone else in this review. According to NIH, exclusively breastfed babies of women who eat no animal products can have very limited B12 reserves and can become deficient very early in life. A review of six small studies of vegan pregnancy found B12 supplements seemed enough to keep mother and cord blood B12 adequate.

Metformin, the diabetes drug that is also used for gestational diabetes, might reduce B12 absorption and blood levels, according to NIH. NIH does not address pregnancy specifically, so the link here runs through the drug's use in pregnancy.

There is no upper intake limit for B12, because its potential for toxicity is low, according to NIH. One unexplained signal sits against that. In a Boston birth cohort of 1,257 mother and child pairs, very high maternal plasma B12 of 536.8 pmol/L or more, measured 2 to 3 days after birth, went with 2.5 times the risk of autism (95% CI 1.4 to 4.5). It is a single cohort, the authors call it hypothesis-generating, and it does not question an adequate intake. It is a reason not to take very large doses without a need.

One more point affects how a test is read. According to NIH, blood B12 tends to drop during pregnancy, sometimes below normal, and usually returns to normal after delivery. A single low result in pregnancy is harder to interpret than the same number outside it.

What expert bodies say

EFSA, the European Food Safety Authority, sets an adequate intake of 4.5 micrograms a day in pregnancy and 5 during breastfeeding, above the 4 set for adults, to cover B12 stored by the fetus and passed into milk. The NIH Office of Dietary Supplements describes the drop in pregnancy, the risk to babies of mothers who eat no animal products, and the effect of metformin. We did not find a WHO or ACOG position on B12 in pregnancy that we could quote, so none is cited here.

How we searched

What would change this answer

• A randomized trial large enough to measure low birth weight and preterm birth. Two trials of about 340 women each cannot tell a benefit from a harm.
• Any trial of B12 to prevent neural tube defects. Today that link rests on observational data alone.
• Trials outside low- and middle-income countries. Every trial in the Cochrane review came from them, and women with plenty of B12 to start with may respond differently. We found no trial now running on B12 and pregnancy outcomes.
• More work on the autism signal at very high blood levels, which so far comes from a single cohort.

What B12 does, where it comes from and who runs short is on the vitamin B12 page.

Sources

1. ev-b12p-01 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of RCTs · n = 272
   Maternal vitamin B12 status: vitamin B12 supplementation during pregnancy may reduce the risk of maternal vitamin B12 deficiency compared to placebo or no vitamin B12 supplementation, but the evidence is very uncertain (25.9% versus 67.9%; RR 0.38, 95% CI 0.28 to 0.51; 2 trials, 272 women; very low-certainty evidence).
   
   Who: pregnant women in low- and middle-income countries (India, Bangladesh, South Africa, Croatia)
   Effect: maternal B12 deficiency RR 0.38 (95% CI 0.28 to 0.51), 2 trials, 272 women; very low-certainty evidence
   Certainty: Five trials, 984 women overall; doses 5-250 ug/day from 8-28 weeks gestation. Biomarker outcome, not a clinical one.
   Cochrane Database Syst Rev, 2024 · checked 2026-10-07 · we read the abstract
2. ev-b12p-02 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of RCTs · n = 344
   Adverse pregnancy outcomes: the evidence is uncertain about the effect on adverse pregnancy outcomes, including preterm birth (RR 0.97, 95% CI 0.55 to 1.74; 2 trials, 340 women; low-certainty evidence), and low birthweight (RR 1.50, 95% CI 0.93 to 2.43; 2 trials, 344 women; low-certainty evidence).
   
   Who: pregnant women in low- and middle-income countries (India, Bangladesh, South Africa, Croatia)
   Effect: preterm birth RR 0.97 (95% CI 0.55 to 1.74), 2 trials, 340 women; low birthweight RR 1.50 (95% CI 0.93 to 2.43), 2 trials, 344 women; low-certainty evidence
   Certainty: Wide intervals in both directions: absence of evidence, not evidence of no effect.
   Cochrane Database Syst Rev, 2024 · checked 2026-10-07 · we read the abstract
3. ev-b12p-03 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of RCTs · n = 284
   Maternal anaemia: there may be little to no difference for maternal anaemia by intervention group, but the evidence is very uncertain (70.9% versus 65.0%; risk ratio (RR) 1.08, 95% confidence interval (CI) 0.93 to 1.26; 2 trials, 284 women; very low-certainty evidence).
   
   Who: pregnant women in low- and middle-income countries (India, Bangladesh, South Africa, Croatia)
   Effect: maternal anemia RR 1.08 (95% CI 0.93 to 1.26), 2 trials, 284 women; very low-certainty evidence
   Certainty: Anemia in these settings is mostly iron-driven; all women got iron and folic acid in the main trial.
   Cochrane Database Syst Rev, 2024 · checked 2026-10-07 · we read the abstract
4. ev-b12p-04 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of RCTs · n = 984
   No trials evaluated the effects of vitamin B12 supplementation during pregnancy on neural tube defects.
   
   Who: pregnant women in low- and middle-income countries (India, Bangladesh, South Africa, Croatia)
   Effect: 0 trials on neural tube defects among 5 included trials
   Certainty: The NTD link rests on observational data only (see ev-b12p-11).
   Cochrane Database Syst Rev, 2024 · checked 2026-10-07 · we read the abstract
5. ev-b12p-05 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 76 trials
   Maternal vitamin B-12 supplementation during pregnancy increased serum cobalamin concentrations (standard mean difference [SMD] 0.39; 95% CI 0.11, 0.68; P=0.01) and reduced deficiency (OR 0.43; 95% CI 0.19, 0.95; P=0.04), with improved B-12 concentrations in milk, especially when administered postpartum (SMD 0.33; 95% CI 0.02, 0.63; P=0.04), but had no consistent effect on infant or cord serum cobalamin concentrations.
   
   Who: healthy pregnant and/or lactating women in low- and middle-income countries
   Effect: maternal serum cobalamin SMD 0.39 (95% CI 0.11 to 0.68); deficiency OR 0.43 (95% CI 0.19 to 0.95); breast milk B12 SMD 0.33 (0.02 to 0.63); no consistent effect on infant or cord B12
   Certainty: 76 trials cover all vitamins; the B12 subset is smaller (number not in abstract). GRADE applied.
   Adv Nutr, 2025 · checked 2026-10-07 · we read the abstract
6. ev-b12p-06 · Meta-analysis or systematic review · systematic review and meta-analysis of controlled trials · n = —
   Despite the prevalence of vitamin B12 deficiency amongst populations with limited intake of animal source foods, no intervention trials have evaluated vitamin B12 supplementation before or during pregnancy.
   
   Who: pregnant women in controlled trials of vitamins B6, B12 and C
   Effect: 0 intervention trials of vitamin B12 before or during pregnancy at the time of search
   Certainty: Historical gap; the trials pooled by Cochrane 2024 were published later.
   Paediatr Perinat Epidemiol, 2012 · checked 2026-10-07 · we read the abstract
7. ev-b12p-07 · Randomized controlled trial(s) · randomized placebo-controlled trial, 50 ug/day oral B12 from <14 weeks gestation to 6 weeks postpartum, Bangalore · n = 366
   Compared with placebo recipients, vitamin B-12-supplemented women had significantly higher plasma vitamin B-12 concentrations at both the second (median vitamin B-12 concentration: 216 vs. 111 pmol/L, P < 0.001) and third (median: 184 vs. 105 pmol/L, P < 0.001) trimesters.
   
   Who: pregnant women <14 weeks gestation in Bangalore, India, all also given iron and folic acid
   Effect: median maternal plasma B12 216 vs 111 pmol/L in the second trimester and 184 vs 105 pmol/L in the third (P < 0.001)
   Certainty: Biomarker outcomes; population with high baseline deficiency.
   J Nutr, 2014 · checked 2026-10-07 · we read the abstract
8. ev-b12p-08 · Randomized controlled trial(s) · randomized placebo-controlled trial, 50 ug/day oral B12 from <14 weeks gestation to 6 weeks postpartum, Bangalore · n = 256
   Among vitamin B-12-supplemented women, the incidence of delivering an infant with intrauterine growth retardation was 33 of 131 (25%) vs. 43 of 125 (34%) in those administered placebo (P = 0.11).
   
   Who: pregnant women <14 weeks gestation in Bangalore, India
   Effect: intrauterine growth retardation 33/131 (25%) vs 43/125 (34%), P = 0.11
   Certainty: Underpowered for growth outcomes; secondary endpoint.
   J Nutr, 2014 · checked 2026-10-07 · we read the abstract
9. ev-b12p-09 · Randomized controlled trial(s) · randomized placebo-controlled trial, 50 ug/day oral B12 from <14 weeks gestation to 6 weeks postpartum, Bangalore · n = 178
   There were no significant differences in any of the subscales of BSID-III between infants born to mothers who received B12 supplementation (n = 78) vs. placebo (n = 100).
   
   Who: infants of women in the Bangalore B12 trial tested with BSID-III at 9 months
   Effect: no significant difference in any BSID-III subscale (78 B12 vs 100 placebo)
   Certainty: Only about half of infants assessed.
   Matern Child Nutr, 2017 · checked 2026-10-07 · we read the abstract
10. ev-b12p-10 · Randomized controlled trial(s) · randomized placebo-controlled trial, 50 ug/day oral B12 from <14 weeks gestation to 6 weeks postpartum, Bangalore · n = 218
    Children of mothers who received oral vitamin B12 supplementation had significantly higher scores on expressive language compared to children of mothers who received placebo (β = 0.14, P = 0.03).
    
    Who: children born to mothers enrolled in the Bangalore B12 trial, assessed with BSID-III at 30 months
    Effect: expressive language beta 0.14 (P = 0.03) vs placebo
    Certainty: Multiple domains tested, no correction stated in abstract; Cochrane rated low certainty.
    Matern Child Health J, 2019 · checked 2026-10-07 · we read the abstract
11. ev-b12p-11 · Observational data · systematic review and meta-analysis of observational studies · n = 6614
    Compared with the non-NTD group, the NTD group exhibited a lower vitamin B12 level [SMD = -0.23, 95% CI (-0.32, -0.14), p < 0.001, I2 = 58.3%] with a statistically significant difference.
    
    Who: mothers of NTD cases and controls in 14 countries
    Effect: maternal B12 SMD -0.23 (95% CI -0.32 to -0.14), I2 58.3%
    Certainty: Case-control designs, blood drawn after outcome in many; association only.
    Nutrients, 2025 · checked 2026-10-07 · we read the abstract
12. ev-b12p-12 · Observational data · systematic review and individual participant data meta-analysis of observational studies · n = 11216
    No linear association was observed between maternal B12 levels in pregnancy and birth weight, but B12 deficiency (<148 pmol/L) was associated with a higher risk of low birth weight in newborns (adjusted risk ratio = 1.15, 95% confidence interval (CI): 1.01, 1.31).
    
    Who: pregnant women in 18 cohorts, individual participant data
    Effect: low birth weight aRR 1.15 (95% CI 1.01 to 1.31) with B12 below 148 pmol/L; no linear association with birth weight
    Certainty: Adjusted associations; authors call for RCTs.
    Am J Epidemiol, 2017 · checked 2026-10-07 · we read the abstract
13. ev-b12p-13 · Observational data · systematic review and meta-analysis of observational studies · n = 10595
    Women with vitamin B12 deficiency were at higher risk for developing GDM when compared with those who were vitamin B12 sufficient (OR, 1.46; 95% CI 1.21-1.79; I2: 59.0%).
    
    Who: pregnant women in 10 observational studies
    Effect: GDM OR 1.46 (95% CI 1.21 to 1.79), I2 59.0%
    Certainty: An earlier dose-response MA (35105943) found highest vs lowest B12 OR 0.77 (0.58 to 1.02), not significant.
    BMC Pregnancy Childbirth, 2022 · checked 2026-10-07 · we read the abstract
14. ev-b12p-14 · Observational data · systematic review and meta-analysis of observational studies · n = —
    Vitamin B12 levels in women with preeclampsia were significantly lower than those in healthy women (mean, -15.24 pg/mL; 95%CI, -27.52 to -2.954; P < 0.015), but heterogeneity between studies was high (I2 = 97.8%; P = 0.0103).
    
    Who: women with preeclampsia vs normotensive pregnant women
    Effect: mean difference -15.24 pg/mL (95% CI -27.52 to -2.954); I2 97.8%
    Certainty: Extreme heterogeneity; direction of causality unknown.
    Nutr Rev, 2021 · checked 2026-10-07 · we read the abstract
15. ev-b12p-15 · Observational data · prospective birth cohort · n = 1257
    Similarly, very high B12 (≥536.8 pmol/L) showed 2.5 times increased risk (95% CI 1.4, 4.5).
    
    Who: mother-child pairs recruited at birth at Boston Medical Center
    Effect: ASD risk 2.5 times (95% CI 1.4 to 4.5) with maternal plasma B12 at or above 536.8 pmol/L vs middle 80th percentile
    Certainty: Single cohort, B12 measured 2-3 days after birth; does not question adequate intake. Reason not to megadose without need.
    Paediatr Perinat Epidemiol, 2018 · checked 2026-10-07 · we read the abstract
16. ev-b12p-16 · Observational data · systematic review of observational studies · n = 6 studies
    Vitamin B12 supplements seemed sufficient in optimizing maternal and umbilical cord vitamin B12 levels amongst vegan mothers.
    
    Who: pregnant women on vegan vs omnivorous diets
    Effect: B12 supplements seemed sufficient to optimize maternal and cord B12 in vegan mothers
    Certainty: Only six small studies.
    Nutrients, 2024 · checked 2026-10-07 · we read the abstract
17. ev-b12p-17 · Position of an expert body · agency fact sheet · n = —
    During pregnancy, serum vitamin B12 levels tend to drop, sometimes to subnormal levels, but they usually return to normal after delivery [35].
    
    Who: pregnant women
    Effect: serum B12 declines during pregnancy, returns to normal after delivery
    Certainty: Physiological drop complicates reading a single B12 test in pregnancy.
    NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-07 · we read the section
18. ev-b12p-18 · Position of an expert body · agency fact sheet · n = —
    The FNB did not establish a UL for vitamin B12 because of its low potential for toxicity [1].
    
    Who: general population
    Effect: no UL set by the Food and Nutrition Board
    Certainty: Applies to pregnancy too; see ev-b12p-15 for an unresolved signal at very high blood levels.
    NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-07 · we read the section
19. ev-b12p-19 · Position of an expert body · agency fact sheet · n = —
    Metformin, an antihyperglycemic agent used as first-line treatment for prediabetes and diabetes, might reduce the absorption of vitamin B12 and significantly reduce serum vitamin B12 concentrations [103].
    
    Who: people taking metformin
    Effect: reduced absorption and serum B12
    Certainty: ODS does not address pregnancy specifically; relevance via metformin use in GDM.
    NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-07 · we read the section
20. ev-b12p-20 · Position of an expert body · agency fact sheet · n = —
    Exclusively breastfed infants of women who consume no animal products might have very limited reserves of vitamin B12 and can develop vitamin B12 deficiency, sometimes very early in life [58].
    
    Who: exclusively breastfed infants of women who consume no animal products
    Effect: very limited infant reserves; deficiency sometimes very early in life
    Certainty: Agency summary; explains why vegan mothers need B12 before and during pregnancy.
    NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-07 · we read the section
21. ev-b12p-21 · Position of an expert body · agency scientific opinion on dietary reference values · n = —
    For pregnancy and lactation, additional cobalamin intakes related to the accumulation of cobalamin in fetal tissues and transfer of cobalamin into breast milk are considered and AIs of 4.5 and 5 μg/day, respectively, are proposed.
    
    Who: pregnant and lactating women in the EU
    Effect: AI 4.5 ug/day pregnancy, 5 ug/day lactation (adults 4 ug/day)
    Certainty: EU value is higher than the US RDA for pregnancy because it is set on biomarkers, not hematology alone.
    EFSA NDA Panel, Scientific Opinion on Dietary Reference Values for cobalamin (vitamin B12), EFSA Journal 2015;13(7):4150 · checked 2026-10-07 · we read the abstract