Whether Down’s screening for a critical risk of trisomy 21 is still possible requires further non-invasive DNA or amniocentesis testing to determine. The Down’s syndrome test does not directly test the chromosomes of the fetus, it is a chromosomal trisomy risk ratio obtained by mathematical operation of the blood test indicators, so the accuracy is not very high, and there are often false positives. If the Down’s syndrome screening test result is a critical risk of trisomy 21, it does not directly confirm the diagnosis of fetal chromosomal abnormality, and the next step of prenatal diagnosis must be made to determine whether the fetus has an abnormality or not, such as non-invasive DNA or amniocentesis, of which amniocentesis is the gold standard of diagnosis and has the highest accuracy, but due to invasive tests, the operation of amniocentesis carries certain risks to the fetus. After that, it is necessary to comprehensively determine whether the fetus has chromosomal abnormalities based on the results of prenatal diagnosis and ultrasonography, and if the abnormality is diagnosed, the fetus cannot be wanted.