Critical risk of trisomy 21 means that the probability of having a child with Down’s syndrome during screening for Down’s syndrome during pregnancy is between high risk and low risk. Critical risk only indicates that the fetus is at a higher risk of developing trisomy 21, but it does not determine whether the fetus has a disorder caused by a chromosomal abnormality, and requires further definitive diagnosis by non-invasive DNA and amniocentesis. Critical risk means that there is a certain level of risk, which means that the possibility of trisomy 21 is relatively small, but there is still a possibility that it may occur, so it is necessary to consider further improvement of the relevant tests to rule out the abnormality. Normally, the accuracy of non-invasive DNA test results is 99%. If the test results indicate a low risk, it is necessary to strengthen pregnancy care, pay attention to a well-balanced diet, and go to the hospital for regular pregnancy checkups. If the test result shows high risk, amniocentesis is required. The accuracy of amniocentesis results can usually reach 100%. However, as amniocentesis is an invasive procedure, it will increase the risk of miscarriage by 0.5%-1%, and should be performed after diagnosis by a doctor. If the amniocentesis results indicate that the fetus is healthy, the mother can continue the pregnancy, but if it suggests that the fetus has Down syndrome, the mother is advised to terminate the pregnancy. 21-Trisomy Syndrome is a chromosomal disorder in which the child suffers from varying degrees of mental retardation and physical developmental abnormalities, which are basically incurable after birth, and it is recommended that screening for 21-Trisomy Syndrome is actively conducted during pregnancy in order to avoid birth of a child with this condition.