The critical risk of trisomy 21 refers to the probability of having a child with Down’s syndrome between high and low risk at the time of Down’s syndrome screening during pregnancy. The critical risk only indicates that the fetus is at a higher risk of developing Trisomy 21, but it cannot determine whether the fetus has a chromosomal abnormality causing the disease, which requires further definitive diagnosis through non-invasive DNA and amniocentesis. Critical risk means that there is a certain level of risk, which means that the likelihood of trisomy 21 is relatively low, but it still has the possibility of occurrence, so further improvement of relevant tests to rule out abnormalities needs to be considered. Usually, the accuracy of non-invasive DNA test results is 99%. If the test results indicate a low risk, you should pay attention to strengthening your pregnancy care, pay attention to a balanced diet, and go to the hospital for regular pregnancy checkups. If the test results indicate a high risk, further amniocentesis is required. The accuracy of amniocentesis test results can usually reach 100%, but since amniocentesis is an invasive operation, it can increase the risk of miscarriage by 0.5% to 1%. If the result of amniocentesis indicates a healthy fetus, the mother can continue the pregnancy, while if it indicates Down syndrome, the mother is advised to terminate the pregnancy. 21-trisomy is a chromosomal disorder with varying degrees of mental retardation and physical developmental abnormalities in the affected child, which is basically incurable after birth, and it is recommended to actively screen for 21-trisomy during pregnancy to prevent the birth of the affected child.