6Shibuya K, Murray CJL. Congenital anomalies. In: Murray CJL,Lopez AD, eds. Health dimensions of sex and reproduction: the global burden of sexually transmitted diseases, HIV, maternal conditions, perinatal disorders and congenital anomalies. Boston :Harvard University Press, 1998 (3): 455-512.
7Cragan JD, Roberts HE, Edmonds LD, et al. Surveillance for anencephaly and spina bifida and the impact of prenatal diagnosis-United States, 1985-1994. MMWR CDC Surveill Summ, 1995, 44 (ss-4): 1-13.
8Berry RJ, Li Z, Erickson JD, et al. Preventing neural tube defects with folic acid in China. N Engl J Med, 1999, 341: 1485-1490.
9Hibbard ED, Smithells RW. Folic acid metabolism and human embryopathy. Lancet, 1968, I, 1254.
10MRC Vitamin Study Research Group. Prevention of neural tube defects., results of the medical resesrch council vitamin study.Lancet, 1991, 338: 131-137.
