Higher preconception vitamin B12 in both parents linked to lower birth defect prevalence

Higher vitamin B12 levels in both prospective parents before conception were associated with a lower predicted prevalence of birth defects in offspring, according to a prospective cohort study published in Annals of Internal Medicine.¹ Maternal folic acid is known to prevent neural tube defects, but how parental folate and vitamin B12 relate to birth defects overall had remained unclear.¹ According to the authors, the findings support the potential importance of both paternal and maternal nutrition in the periconceptional period and early pregnancy.³

Vitamin B12 levels and birth defect prevalence in the Shanghai Preconception Cohort

Researchers from Children's Hospital of Fudan University analyzed 3032 couples (73 birth defect cases) with biomarkers sampled within 4 months before conception, along with 17 765 women (327 cases) sampled at 4 months' gestation or earlier.¹ Birth defects were ascertained among live births, stillbirths, and abortions due to fetal abnormalities, and predicted prevalences were estimated with weighted logistic regression.¹

Predicted prevalence fell from 49.6 to 16.2 cases per 1000 pregnancies across preconception maternal vitamin B12 categories, from the lowest (<148 pmol/L) to the highest (≥590 pmol/L).⁴ Paternal vitamin B12 showed a similar but attenuated pattern, with predicted prevalence declining from 55.5 to 24.0 cases per 1000 pregnancies.⁴

Red blood cell folate and postconception vitamin B12 findings

Patterns for preconception parental red blood cell (RBC) folate were imprecise.⁴ For postconception maternal RBC folate, predicted prevalence was lower at 906 to 1131 nmol/L than at levels below 453 nmol/L.⁴ Higher postconception maternal vitamin B12 was also associated with lower predicted prevalence.⁴

Folic acid and vitamin B12 supplementation in preconception counseling

The study's patient summary states that mothers should continue folic acid supplementation before and after conception, and that vitamin B12 supplementation after conception may also be needed to reduce birth defect risk.² It also advises patients to review any vitamin supplementation with a clinician.² The paper is accompanied by an editorial in the same journal.³

References

1. Chen H, Chen X, Zhang Y, et al. Periconception parental red blood cell folate, vitamin B12, and birth defects in offspring: a prospective cohort study. Ann Intern Med. Published online September 1, 2026. doi:10.7326/ANNALS-25-05243

2. Summary for Patients: vitamins and birth defects. Ann Intern Med. Published September 1, 2026. doi:10.7326/ANNALS-25-05243-PS

3. American College of Physicians. Higher vitamin B12 levels in both parents are associated with lower risk of birth defects. Newswise. August 31, 2026. Accessed September 21, 2026. https://www.newswise.com/articles/higher-vitamin-b12-levels-in-both-parents-are-associated-with-lower-risk-of-birth-defects

4. Higher parental vitamin B12 tied to lower prevalence of birth defects. HealthDay News. September 2026. Accessed September 21, 2026. https://www.endocrinologyadvisor.com/news/higher-parental-vitamin-b12-tied-to-lower-prevalence-of-birth-defects/