If the results of the Down screening test for Trisomy 21 show a high risk, either non-invasive DNA testing or amniocentesis can be performed. There are advantages and disadvantages between the two, which need to be weighed and chosen under the guidance of a doctor: 1. Non-invasive DNA testing: The test is performed by taking the serum of the pregnant woman, and based on her age, height, weight and gestational week, a comprehensive analysis is performed to detect abnormalities in the number of chromosomes to assess and determine the risk of fetal trisomy 21. The advantage is that it is less invasive, suitable for most women, and does not cause damage to the fetus, so when the result of Down screening test is high risk, this method can be preferred; 2, amniocentesis: amniocentesis requires amniotic fluid extraction through the uterine wall for examination, the test results are more accurate than non-invasive DNA testing, but there is a certain amount of trauma, and pregnant women need to rest for 3-4 days after the test. It is usually less invasive and acceptable to most patients, but in rare cases, uterine infection or miscarriage may occur.