Trisomy 21, also known as congenital dysgenesis, is the most common type of chromosomal disorder. Children with this condition have varying degrees of mental retardation and physical developmental delays. The child has a special congenital dysmorphic appearance, which is characterized by a round face, flat head, small eye slits, upward slanting, flat nose, wide eye spacing, small mouth, stretched tongue, short stature, and loose joint ligaments in the extremities. About 1/3 of the children will have congenital heart disease or other malformations, and are susceptible to infectious diseases because of the child’s generally low immune function. Since there is no treatment for trisomy 21 at all. Therefore, prenatal and preparatory examinations are particularly important and are not recommended for pregnancies at advanced ages. If the mother is over 35 years old or the father is over 45 years old when she is pregnant with the baby, both need to have their maternity checkups on time, with Down screening and amniocentesis.