What ultrasound finding is indicative of Trisomy 13?

The presence of overlapping digits is a notable ultrasound finding associated with Trisomy 13, also known as Patau syndrome. This particular phenotype occurs due to the extra chromosome and can manifest as significant physical anomalies. Overlapping digits typically involve a particular arrangement where the second and third digits on the hand cross over each other, a characteristic feature observed in some infants with this chromosomal condition.

While other findings such as a single umbilical artery, sandal gap, and echogenic intracardiac focus can be seen in various other conditions or syndromes, they are not specific indicators of Trisomy 13. For example, a single umbilical artery can sometimes be detected in normal pregnancies or may relate to other syndromes, and a sandal gap is more closely associated with Trisomy 21 (Down syndrome). An echogenic intracardiac focus is often considered a soft marker and is also not specific for Trisomy 13. Thus, overlapping digits serve as a more definitive indicator when evaluating for Trisomy 13 during a prenatal ultrasound evaluation.