Trisomy 21, also known as Down syndrome, is one of the most common chromosomal disorders in humans, caused by abnormalities in the number of chromosomes that carry genes. The karyotype of the chromosomes is (46,XY) or (46,XX) for males and females, respectively, whereas in patients with trisomy 21, the karyotype is (47,XX,+21) or (47,XY,+21), which is caused by the non-separation of chromosome 21 during meiosis, resulting in an abnormal egg. The clinical manifestations and characteristics of a typical child with trisomy 21 are as follows: firstly, the child with trisomy 21 has a much lower level of intelligence than a normal child, and as he or she grows older, the lower level of intelligence becomes more pronounced; secondly, the child has delayed physical development, delayed motor and sexual development, and often lags behind in bone age, and often has problems with problem solving and feeding. Second, the physical development is delayed, the motor development and sexual development are delayed, and the bone age is often behind the age. Third, the typical peculiar facial features. Short stature, short limbs, smaller than normal head circumference, wide eye spacing, low nasal bridge, small eye fissures, lateral upward sloping eyes, small external ears, narrow hard palate, tongue often sticking out of the mouth, salivation, thin and less hair, etc. At present, women can be screened for Down’s syndrome during pregnancy, i.e., the fetus can be diagnosed with trisomy 21 through techniques such as amniocentesis.