- Design
- Prospective cohort
- Population
- 3032 couples preconception and 17,765 women in early pregnancy, Shanghai
- Primary outcome
- Birth defects in live births, stillbirths and terminations
- Effect
- 49.6 vs 16.2 per 1000 pregnancies, lowest vs highest maternal B12
The Shanghai Preconception Cohort measured vitamin B12 and red cell folate in 3032 couples within four months before conception and in 17,765 women up to four months' gestation. It was published in Annals of Internal Medicine in September.
Predicted prevalence of birth defects fell from 49.6 to 16.2 per 1000 pregnancies between the lowest (<148 pmol/L) and highest (≥590 pmol/L) maternal preconception B12 categories. Paternal B12 showed a weaker version of the same pattern. After conception, maternal red cell folate of 906 to 1131 nmol/L was associated with 16.5 versus 25.7 per 1000 below 453 nmol/L.
This is observational, and residual confounding is the stated limitation. It does not show that B12 supplements prevent birth defects. It does support attention to B12 status before pregnancy where deficiency is common, as it is in vegetarian populations and in India.
- Continue folic acid before conception as standard.
- Consider B12 status in women planning pregnancy who are vegetarian or on metformin.
- Treat confirmed B12 deficiency before conception on its own merits.
- Do not promise that B12 supplements prevent birth defects.
Why it matters
It raises vitamin B12, not only folate, as a preconception nutrient worth checking.
Don't overread it
This was observational; it cannot show that correcting low B12 prevents birth defects.
The statistics, in plain English
Predicted prevalences come from a statistical model and the preconception couple group had only 73 birth defects, so the estimates are imprecise. People with high B12 may differ in diet, income and health in ways the model cannot fully remove.
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