根据有关先天畸形的报告,在英格兰和成尔士,胎儿神经营缺陷(NTD)的发生率从1964～1972年间的万分之31.5降到了1986年的万分之6.2,其部分原因是由于在这个时期内普遍开展了产前诊断和受累胎儿做了人工流产。NTD的发生率降低的原因是由于采取了产前筛查和诊断还是由于孕中期NTD的发生率降低,目前尚不清楚,因此,我们在1985年里做了调查,以便弄清实际情况。我们的调查主要根据三个方面的资料: According to a report on congenital malformations, the incidence of fetal neuropsychiatric malpractice (NTD) in England and Cheshire dropped from 31.5 in 1964-1972 to 6.2 in 1986, in part because during this period Prenatal diagnosis and fetal abortions were routinely performed within abortion. The reason for the reduced incidence of NTD is due to prenatal screening and diagnosis or to a reduction in the incidence of NTD in the second trimester of pregnancy. It is not yet clear, therefore, we conducted a survey in 1985 to find out the actual situation. Our survey mainly based on three aspects of information: