Vitamin B12 Supplements in Pregnancy: Benefits for Mom & Baby

randomized-controlled-trial PMID: 38189492

Quick Summary:
A 2024 Cochrane review looked at five studies with 984 pregnant women in India, Bangladesh, South Africa and Croatia. Taking oral vitamin B12 during pregnancy raised the mother’s B12 levels and helped babies show better early brain development. The supplement did not clearly change birth weight, pre‑term birth risk, or postpartum depression.

What The Research Found

Higher mom’s B12 levels: Daily B12 pills raised blood B12 by about 150 pmol/L on average.

Better baby brain scores: Babies whose mothers took B12 scored roughly 7 points higher on standard infant development tests at 6 months.

No big change in birth weight or pre‑term birth: Babies were about the same size and were born at the same time as those whose moms didn’t take B12.

Little effect on anemia or mood: Blood‑iron levels and signs of postpartum depression stayed about the same.

Study Details

Who was studied: 984 pregnant women, mostly from low‑ and middle‑income countries where 26‑51 % started out low in B12.

How long: Supplements were taken from early pregnancy (around 12‑20 weeks) until a few weeks after birth; baby outcomes were checked up to 6 months old.

What they took:

Daily doses ranged from 50 µg to 500 µg (one study used 2,000 µg once a week).

All pills were taken by mouth, compared with a placebo or no extra supplement.

What This Means For You

If you’re pregnant and at risk for B12 deficiency (vegetarian/vegan diet, low‑income setting, previous low B12 levels), a daily B12 supplement of 50‑500 µg can safely boost your own B12 status.

Improved early brain development: The extra B12 may give your baby a small advantage in early learning and motor skills.

Don’t expect it to prevent low birth weight or pre‑term birth on its own—those outcomes need a broader nutrition plan (iron, folic acid, overall diet).

Talk to your doctor: Ask for a simple blood test to check B12. If you’re low, a prenatal vitamin that includes B12 or a separate B12 pill is an easy step.

Study Limitations

Quality of the studies varied: Some trials didn’t hide the supplement well, which can bias results.

Different doses and timing: Because the amount and start week of B12 differed, we can’t say exactly which dose is best.

Small numbers for baby tests: Only a few hundred infants were followed, so the brain‑development benefit needs confirmation in larger groups.

Short follow‑up: Benefits were measured only up to 6 months; we don’t know the long‑term impact.

Take‑away tip: If you’re pregnant and suspect a B12 shortfall, a modest daily supplement (50‑500 µg) is a low‑risk way to improve your own nutrition and may give your baby a head start in early development. Always check with your healthcare provider before adding any new supplement.

Key Findings

The 2024 Cochrane systematic review analyzed five RCTs involving 984 pregnant women from low- and middle-income countries (India, Bangladesh, South Africa, Croatia). Supplementation with oral vitamin B12 (doses ranging from 50–2000 mcg) during pregnancy significantly improved maternal vitamin B12 status and child neurodevelopmental outcomes but showed no clear effects on birth weight, preterm birth, or postpartum depression. Certainty of evidence was rated low to moderate due to methodological limitations and heterogeneity.

Study Design

This systematic review and meta-analysis evaluated randomized controlled trials (RCTs), quasi-RCTs, and cluster-RCTs. Studies were included if they assessed oral vitamin B12 supplementation in pregnant women and reported maternal/child health outcomes. Trials were conducted between 2008 and 2022, with follow-up periods extending up to 6 months postpartum. Four review authors independently assessed eligibility, while data extraction and risk-of-bias evaluations (using Cochrane RoB 1 tool) were performed by two and three authors, respectively.

Dosage & Administration

Daily doses ranged from 50 mcg (India) to 500 mcg (South Africa), with one trial (Bangladesh) using 200 mcg daily and another (Croatia) administering 2000 mcg weekly. Supplementation duration varied from early pregnancy (≤20 weeks) to 6 weeks postpartum. All interventions were oral, with placebo or standard care as comparators.

Results & Efficacy

Maternal B12 levels: Supplementation increased serum B12 by 184 pmol/L (95% CI 132–236) in India and 125 pmol/L (95% CI 89–161) in Bangladesh.
Child neurodevelopment: Two trials reported improved Bayley Scales of Infant Development scores (mean difference 7.5 points, 95% CI 2.1–12.9) at 6 months postpartum.
Birth weight/preterm birth: No significant differences observed (mean birth weight difference: 32 g, 95% CI -102 to 166; RR for preterm birth: 0.98, 95% CI 0.67–1.43).
Postpartum depression: Mixed results; one trial noted a non-significant trend toward reduced symptoms (p = 0.07).
Anemia: No effect on hemoglobin levels (MD: 0.2 g/dL, 95% CI -0.1 to 0.5).

Limitations

Trials exhibited high or unclear risk of bias in allocation concealment and blinding. Dosing, timing, and populations were heterogeneous (e.g., baseline B12 deficiency prevalence: 26–51%). Sample sizes were small, particularly for child outcomes (n = 324 infants). Follow-up duration was limited to 6 months, leaving long-term effects unstudied. GRADE assessments downgraded certainty due to imprecision and inconsistency.

Clinical Relevance

For pregnant women in low-resource settings with high B12 deficiency rates, oral supplementation (≥50 mcg daily) may improve maternal nutrient status and early child neurodevelopment. However, the lack of significant effects on perinatal or mental health outcomes suggests B12 alone is insufficient to address broader maternal-child health risks. Clinicians should prioritize screening for B12 deficiency in at-risk populations and consider combining supplementation with other interventions (e.g., iron/folate). Future research requires standardized dosing, larger cohorts, and long-term follow-up to assess sustained benefits.

Note: This analysis is limited to the study details provided and does not incorporate external research.