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The mothers of 17%of cases and 3%of controls reported knowledge of the folic acid-NTD hypothesis and were excluded from further analysis.For daily ise of multivitamins containing folic acid in the periconceptual period(28 days before through 28 days after the last menstrual period),the relative risk(RR)(and 95%confidence interval)was 0.4(0.2to 0.6).The most commonly used dise of folic acid was 0.4mg,and RR estimate was 0.3(95% confidence interval,0.1 to 0.6).For dietary folate,there was a dose- related decline in risk according to the quintile intake(P for trend=.02). These findings suggest that daily periconceptual intake of 0.4 mg of folic acid(the dose most commonly contained in over-the-counter multivitamin preparations)reduces the risk of occurent NTDs by approximately 60%.A relatively high dietary intake of folate may also reduce the risk. |
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