The incidence of trisomy 18 is 1 in 6,000 and the proportion is very small, that is, the 18th pair of autosomes becomes 3, which is a chromosomal mutation, and is related to the age of the pregnant woman (the older the age, the higher the incidence), mostly seen in girls, the ratio of male to female children is 1:3. The manifestations are: prominent posterior head, wide spacing between the eyes, small jaw, congenital heart disease, mental retardation, delayed motor function development, low birth Some children may have cleft lip, cleft palate, umbilical hernia and other symptoms.