In order to avoid the birth of defective babies, China currently adopts the “tertiary prevention” strategy recommended by the World Health Organization. Primary prevention refers to pre-conception health care and genetic risk assessment, such as marriage screening, professional counseling at genetic research institutes before pregnancy, and appropriate folic acid supplementation for women of appropriate age. Secondary prevention refers to relying on clinical testing and diagnostic techniques during pregnancy to reduce the birth of defective children by screening pregnant women for blood biochemical indicators, chromosomal abnormalities and ultrasound during early and mid-pregnancy. Tertiary prevention refers to the early diagnosis and treatment of newborns already born to avoid or mitigate disability. Some defective babies are caused by folic acid deficiency, such as some neural tube malformation babies, which can be completely prevented if parents receive professional guidance before conception. In the current situation, there is no effective treatment for most genetic diseases, such as Down’s syndrome, and the proven methods are prenatal screening and prenatal diagnosis to minimize the birth of abnormal fetuses. Prenatal screening is only a risk assessment for fetal malformations or defects, not a diagnosis. Those screened at high risk are subjected to further prenatal diagnosis. Prenatal diagnosis is a diagnosis of whether the fetus has genetic disorders and congenital defects after pregnancy. Currently, the more common method is to obtain amniotic fluid or cord blood for prenatal diagnosis of the fetus at 16-22 weeks of gestation through prenatal diagnosis techniques. Prenatal diagnosis is required in one of the following cases: 1. The mother-to-be is over 35 years old. 2. One of the couple has chromosomal abnormalities or carriers, or one of the couple has congenital metabolic diseases. 3.Pregnant women with abnormalities suggested by ultrasound. 4.Pregnant women who have given birth to anencephalic children, hydrocephalus, spina bifida, cleft lip, cleft palate, congenital heart disease and other abnormalities. 5.Prenatal screening suggests high risk of fetal malformation: for example, serological screening suggests high risk of fetal trisomy 21, trisomy 18, trisomy 13 and open neural tube malformation. 6. Pregnant women who were exposed to large doses of chemical agents, radiation or severe viral infections in early pregnancy. 7, Pregnant women with family history of genetic disease or history of consanguineous marriage. 8, Pregnant women with unexplained miscarriage, stillbirth, malformation and a history of neonatal death.