The minimum duration of supplementation necessary for prevention is not known. Although most national health authorities recommend that women take extra folic acid for at least 4 weeks before conception and until week 12 of pregnancy, supplementation for a shorter duration before closure of the neural tube may also be effective. Until more data are available, the official guidelines should be followed. Given the estimate that approximately half of all pregnancies are unplanned, however, it is important that a woman who has not been taking extra folic acid and who suspects that she may be pregnant immediately starts taking a folic acid supplement. This point requires greater emphasis.
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