Neural-tube defects and vitamins: the need for a randomized clinical trial.

It has been suggested that taking extra vitamins around the time of conception may reduce the risk of fetal neural-tube defects. We have examined the evidence for this and conclude that there is considerable doubt about the efficacy of such a regimen. Also, it cannot be assumed that the taking of extra vitamins has no adverse medical effects. We give reasons for our view that a large randomized clinical trial is ethical and the only satisfactory way of resolving the matter. The Medical Research Council is currently conducting such a study in centres in Britain and abroad, involving women who have already had a pregnancy with a fetal neural-tube defect. The design of the Medical Research Council study is described briefly.