Vitamins During Pregnancy and Neural Tube Defects

Tb the Editor.— We were interested to read the article by Milunsky et al, 1 which demonstrated that multivitamins with folic acid, taken in the first 6 weeks of pregnancy, are associated with a significant reduction in the birth prevalence of neural tube defects (NTDs). We congratulate the authors on a fine piece of work. This prospective population occurrence study complements well the intervention study by ourselves and our colleagues, 2 which has consistently shown a reduced recurrence of NTDs in at-risk women specifically given multivitamins and folic acid supplementation in the periconceptional period. Milunsky et al note that their results differ from a retrospective case-control study by Mills et al, 2 which showed no positive effect on NTDs of periconceptional multivitamins, and they suggest two reasons. We wish to propose a third, the evidence for which we find apparent in our study. The effects of vitamin therapy are more