The main reasons for failure of Down’s syndrome screening include older age, inconsistent information, poor physical condition and chromosomal abnormalities. 1. Older age: older age of pregnant women is one of the main reasons for failure of Down’s syndrome screening. The older the pregnant woman is, the worse her ovarian function is, and the quality of her follicles decreases accordingly. The probability of failing a Down’s syndrome test after pregnancy increases significantly. Generally speaking, it is not meaningful for pregnant women over 35 years old to do Down’s syndrome screening, and amniocentesis is recommended. 2. Inconsistent information: The age, weight and gestational week provided by the pregnant woman during the Down’s syndrome screening do not fully match the actual situation, resulting in errors in the Down’s syndrome screening results. 3. Poor health condition: The health condition of the pregnant woman is not very good when doing the Down’s syndrome test. If the pregnant woman has a cold, it will affect the accuracy of the test results. 4. Chromosomal abnormality: chromosomal abnormality of the fetus itself leads to, if the fetus has abnormality, the indexes of the blood test will usually have abnormality, so the risk value of the test result will be higher. Therefore, in the clinic, if there is a failure of Down’s syndrome, you should go to the hospital in time for examination and treatment under the guidance of the doctor.