A randomised trial of low dose folic acid to prevent neural tube defects. The Irish Vitamin Study Group.

A randomised trial was initiated in Ireland in 1981 to determine if periconceptional supplementation with either folic acid alone or a multivitamin preparation alone could reduce the recurrence risk of neural tube defects (NTDs) in women with a previously affected pregnancy from 5.0% to 1.0% or less. The trial was concluded before the initial target number of study subjects was reached and without a clear treatment effect being observed. A total of 354 women were randomised to receive one of three treatments: folic acid, multivitamins without folic acid, and folic acid plus multivitamins. At the end of the trial 257 women had had a first trial pregnancy outcome (261 infants/fetuses) where the presence or absence of NTDs was ascertainable. There was one NTD recurrence in the 89 infants/fetuses of women in the multivitamin group and no recurrence in the 172 infants/fetuses of women in the folic acid groups, a non-significant difference. Otherwise eligible women who were pregnant when first contacted constituted a non-randomised control group; there were three recurrences among the 103 infants in this group. The difference in the recurrence rate between the folic acid groups and the non-randomised controls was statistically significant but we have reservations about the validity of this comparison. Although our findings do not provide clear evidence of a protective effect of folic acid supplementation they are consistent with those of the Medical Research Council (MRC) trial which demonstrated the efficacy of folic acid in preventing recurrence of NTDs and they raise the possibility that folic acid may be protective at a much lower dosage than that used in the MRC trial.