This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ULTRASOUND, Subject name: Radiology
Which of the following ultrasound marker is associated with greatest increased risk for Trisomy 21 in fetus: 
Select and explain. 
A. Echogenic foci in hea, B. Hyperechogenic bowel, C. Choroid plexus cysts, D. Nuchal skin fold
D: Nuchal skin fold
Answer: D: Nuchal skin fold 
Explanation: Increased nuchal skin fold confers the highest risk of aneuploidy and is the most powerful second trimester ultrasound marker, > 99% specificity for Down Syndrome. The probability of Down Syndrome is increased when multiple soft markers are present.