Trisomy 21 high risk refers to the higher probability that the fetus has chromosome 21 abnormality and has a higher chance of developing trisomy 21 after the pregnant woman has undergone Down’s syndrome screening. 21-trisomy high risk groups include the following: 1, the mother has a history of viral infections, such as influenza, rubella, herpes, etc. during pregnancy; 2, the couple is relatively old and the mother belongs to The mother has a history of multiple stillbirths and stillbirths, or a history of habitual abortion.