Which ultrasound finding is often associated with genetic syndromes like trisomy 21?

Syndactyly, the fusion of fingers or toes, is a common physical finding that can be associated with various genetic syndromes, including trisomy 21, also known as Down syndrome. The presence of syndactyly may indicate an underlying genetic condition, as it is part of the spectrum of developmental anomalies that can accompany chromosomal abnormalities.

Trisomy 21 is characterized by specific physical features and health issues, which can include a variety of limb malformations such as syndactyly. Identifying these physical traits through ultrasound or postnatal examination aids in assessing the risk of genetic syndromes and allows for appropriate counseling and management for expecting parents.

Though the other findings mentioned—caudal regression, atrial septal defect, and coarctation of the aorta—are associated with certain genetic syndromes or congenital conditions, they are not as directly linked to trisomy 21 as syndactyly. Caudal regression syndrome is primarily related to maternal diabetes and not directly related to trisomy 21. Atrial septal defects and coarctation of the aorta may be found in some cases but are more broadly associated with different heart defects rather than being specific indicators of Down syndrome.