Trisomy 18 is a fetal trisomy 18, as the name implies, is an extra chromosome 18, three, normal people including fetuses are diploid are two. trisomy 18 is also a chromosomal abnormality, usually in the fetal stage will be self-elimination, fetal death in the womb. Even if the fetus survives, it will not live long after delivery, but very few chimeras survive, and even if they do, they are multiply malformed. The clinical manifestations are usually growth disorders, mental retardation, hypertonia, renal malformations, etc. Most of the children also have congenital heart disease. Prenatal diagnosis can be made by amniotic fluid or chorionic villus chromosomes, and the pregnancy can be terminated immediately after detection during gestation.