The reason for such a screening result is: first, the fetus is indeed suffering from trisomy 21, so there is a high risk of screening results; second, it may be caused by external factors, such as the mother’s age, poor ovarian function, and the quality of the discharged eggs. In addition, the actual age, week of gestation, weight and other indicators provided by the pregnant woman are not accurate; the technical level and medical equipment of the hospital where the Down’s syndrome screening was performed are limited, which affects the accuracy of the test results.