Down’s syndrome is a chromosomal abnormality in which an extra chromosome of the 21st pair in the body causes congenital stupidity. The causes of Down’s syndrome include genetic factors, environmental factors, fetal factors, maternal factors, etc. I. Congenital genetic factors: If there are chromosomal abnormalities in the family or parents, especially abnormalities in chromosome 21, the probability of Down syndrome in the fetus will be very high. Second, acquired factors: 1, environmental factors: If a woman is exposed to chemical substances, drugs or physical stimuli during pregnancy, especially in the early stages, such as radioactive radiation, drugs or the occurrence of viral infections, resulting in chromosomal non-separation in the child, is also a very common reason for the occurrence of Down’s syndrome; 2, fetal factors: parents are normal and do not have chromosomal abnormalities, but chromosomal abnormalities can also occur, possibly due to fetal 3. Maternal factors: If a woman is over 35 years old, she is of advanced maternal age, which can easily lead to chromosomal non-separation of the fetus.