1. Advanced maternal age (age ≥ 35 years). 2.High risk of Down’s syndrome screening during pregnancy. 3.Ultrasound suggests abnormal fetal development or fetus with suspected malformation. 4.One of the couple is a chromosomal abnormality or balanced translocation carrier. 5.Known or suspected genetic diseases exist in the family. 6. Excessive or low amniotic fluid. 7.History of adverse pregnancy (stillbirth, stillbirth, neonatal death and birth of malformed children and children with chromosomal abnormalities). 8.Exposure to substances that may cause congenital defects in the fetus during early pregnancy.