What is a classic ultrasound finding for trisomy 18?

Trisomy 18, also known as Edwards syndrome, is associated with a variety of congenital abnormalities, many of which can be assessed through ultrasound. A classic finding for this condition is the presence of cardiac defects, which are observed in a significant number of affected individuals. These defects may include structural abnormalities of the heart such as ventricular septal defects, atrial septal defects, and tetralogy of Fallot. Detecting these cardiac anomalies at the prenatal ultrasound can be crucial in identifying pregnancies at higher risk for trisomy 18 and facilitates further genetic counseling and management.

While short humeral length and other findings like the sandal sign may also occur in trisomy 18, the association of cardiac defects with this condition is markedly prevalent and often emphasized in clinical practice and literature. This emphasis stems from the high incidence of these anomalies in affected patients, making them one of the key features relied upon for prenatal diagnosis.