With Down’s syndrome screening, a low risk result means that it is normal and further testing is usually not needed, but low risk does not necessarily mean no risk. The incidence of fetal malformations or chromosomal abnormalities is relatively low, sometimes one in tens of thousands, so the probability of this is very low, and it is only possible for one fetus to be abnormal among thousands or tens of thousands of people. If all these people need to undergo further tests, a lot of financial and material resources will be wasted, so as long as the non-invasive DNA is low-risk, there is usually no need to undergo further tests.