Which sign is caused by thickening of the nuchal fold in the fetus and is associated with chromosomal abnormalities?

• A. Nuchal edema
• B. Nuchal translucency
• C. Nuchal cyst
• D. Nuchal mass

Answer: (A)

Thickening of the nuchal fold is best described as nuchal edema. On ultrasound, edema of the posterior neck appears as increased, diffuse subcutaneous tissue thickness, giving a swollen appearance at the nuchal region. This finding is a soft ultrasound marker that can be associated with chromosomal abnormalities, most notably trisomy 21, and prompts further evaluation or genetic testing when present with other clues.

Nuchal translucency refers to a fluid-filled space behind the neck seen in the first trimester and is a separate marker used early in pregnancy. A nuchal cyst or nuchal mass would present as a discrete lesion rather than diffuse fold thickening and would have different implications and imaging characteristics.