pediatrics
Trisomy 18
Introduction
Trisomy 18 is caused by an extra chromosome 18 and is usually associated with intellectual disability, small birth size, and various congenital anomalies, including severe microcephaly, heart defects, prominent occiput, low-set malformed ears, and a characteristic pinched facial appearance. Prenatal diagnosis is with cytogenetic testing; postnatal diagnosis is with peripheral blood testing. Treatment is supportive. (See also Overview of Chromosomal Abnormalities .) Trisomy 18 occurs in approximately 4.1/10,000 pregnancies (based on data from induced abortion for fetal anomalies, stillbirths, and live births) ( General references ). More than 95% of affected children have complete trisomy 18 ( 