What ultrasound finding is characteristic of Trisomy 18?

The characteristic ultrasound finding associated with Trisomy 18, also known as Edwards syndrome, is rocker-bottom feet. This physical feature is particularly notable in affected infants and arises due to abnormal development of the foot's skeletal structure. The heel is prominent and the toes are typically curled under, giving the foot its distinctive "rocker-bottom" appearance.

While other findings can be associated with various conditions or syndromes, rocker-bottom feet are classically highlighted in discussions about Trisomy 18 due to their prevalence and recognizability in prenatal screenings. This feature is often identified during detailed fetal anatomy scans, making it a significant marker for this chromosomal abnormality.

Holoprosencephaly is more commonly associated with Trisomy 13, while absent nasal bone is typically linked to Trisomy 21 (Down syndrome). Echogenic kidneys can be indicative of various renal abnormalities but are not specific to Trisomy 18. Thus, rocker-bottom feet stand out as the defining sonographic marker for this condition.