# MRC Vitamin Study (1991)

Study · id `maternal:mrc-vitamin-study` · Maternal & Newborn Atlas · release `c7fb95f1d15a7d13` (public)

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Also called: MRC Vitamin Study Research Group trial

Browse, life stage: Preconception; Pregnancy  
Browse, care area: Before pregnancy  

## In plain language

A large international trial that tested whether folic acid, taken around the time of conception, prevents neural tube defects in women who had already had an affected pregnancy. Women were given at random folic acid, a mixture of seven other vitamins, both, or neither. Fewer pregnancies were affected in the folic acid groups.

## Technical summary

Randomised, double-blind prevention trial with a factorial design at 33 centres in seven countries, reported in 1991. 1817 women at high risk because of a previous affected pregnancy were allocated at random; 1195 had a completed pregnancy in which the fetus or infant was known to have or not have a neural tube defect. 27 of these had a defect, 6 in the folic acid groups and 21 in the two other groups (relative risk 0.28, 95% CI 0.12 to 0.71). The other vitamins showed no significant protective effect (relative risk 0.80, 95% CI 0.32 to 1.72). The PubMed abstract gives no folic acid dose, no registry number and no per-group denominators, so none are recorded. Only the abstract was read.

## Key facts

- Design: Randomised, double-blind prevention trial with a factorial design: folic acid, a mixture of seven other vitamins (A, D, B1, B2, B6, C and nicotinamide), both, or neither.
- Phase: Not reported
- Enrolled: 1817 women at high risk of a neural tube defect pregnancy (randomized count; Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. MRC Vitamin Study Research Group, snapshot `maternal:pubmed-1677062-2026-10-14`, retrieved 2026-10-14)
- Started: Not reported
- Primary completion: Not reported
- Completion: Not reported
- Countries: Not reported
- Care setting: 33 centres in seven countries; the abstract does not name them or describe the settings. (Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. MRC Vitamin Study Research Group, snapshot `maternal:pubmed-1677062-2026-10-14`, retrieved 2026-10-14)
- Registry status: Not reported

## Connected pages

- Tests folic acid taken around the time of conception: Folic acid supplementation before and in early pregnancy (`maternal:folic-acid-supplementation`)
- Counts neural tube defects (anencephaly, spina bifida, encephalocele) in the pregnancies: Neural tube defects (fetus) (`maternal:neural-tube-defects`)

## Provenance

Content hash: f18815a72a4e19fd02fe5df90693f4079ab8173bfbbaa5cb0fce42ca7e7268ed
Last substantive edit: 2026-10-14
Evidence last checked: 2026-10-14