Prenatal Sonographic Features of Trisomy 18

Trisomy 18, the second most common autosomal trisomy, is associated with multiple severe structural defects. Most fetuses of trisomy 18 can have one or more sonographically detectable structural abnormalities. This article provides an overview of the common sonographic features of the fetal trisomy 18, with major and minor structural abnormalities including cardiac anomalies, malformations of the central nervous system, facial anomalies, gastrointestinal anomalies, limb anomalies, intrauterine growth restriction, choroid plexus cysts and increased nuchal translucency or cystic hygroma. Several diseases may have phenotypic overlaps with trisomy 18 syndrome, including trisomy 18-like syndrome, Pena-Shokeir syndrome type I and arthrogryposis multiplex congenita. In addition, sex bias is significantly observed in trisomy 18 live births, and prenatal selection against male fetuses has been documented to be associated with more complex congenital anomalies. Because of the lethal birth defects in trisomy 18, prenatal ultrasound is a valuable tool to detect a variety of congenital structural malformations of trisomy 18 throughout the gestation, and early sonographic identification of major structural defects and determination of the fetal sex can provide an appropriate genetic counseling and a more reasonable management for the pregnant women.