The results of a randomized double-blind prevention trial conducted at 33 centers in seven countries to determine the effects of folic acid supplements around the time of conception in the prevention of neural tube defects is reported by the MRC Vitamin Study Research Group, Department of Environmental and Preventive Medicine, Medical College of St. Bartholomew’s Hospital, London EC1, UK. A total of 1,817 women at high risk of having a pregnancy with a neural tube defect were allocated at random to one of four groups - folic acid, other vitamins, both, or neither. Of 27 mothers giving birth to a child with a neural tube defect, six were in the folic acid groups and 21 in the two other groups, a 72% protective effect. Other vitamins showed no significant protective effect. Capsules for those in the folic acid group contained 4 mg of folic acid, one a day until 12 weeks of pregnancy. 
COMMENT. This study establishes the specific role of folic acid in the prevention of neural tube defects. Folic acid supplementation in a dose of 4/mg/day is now recommended for all women who have had a previously affected pregnancy, and the diet of all women who may bear children should contain an adequate amount of folic acid. An editorial in this issue of The Lancet comments that this supplement did not prevent all neural tube defects and six unsuccessful cases were not accounted for by unusually low serum folic acid concentrations. A heterogeneous aetiology for this group of disorders is suggested. The dosage of folic acid necessary to prevent neural tube defects is not entirely established, and the optimal duration of treatment before conception is uncertain. Can culturally appropriate dietary guidelines be prepared as a matter of urgency for all ethnic groups? Can the requisite folic acid be eaten in food instead of given as a supplement? Providing specific dietary advice about the prevention of malformations to women before pregnancy is a challenging public health problem.