This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Impoant Genetic Syndromes, Subject name: Pediatrics
Among the following, the most sensitive antenatal USG finding of Trisomy 21 is: 
Select and explain. 
A. Absent nasal bone, B. Thickened nuchal fold, C. Sho femur, D. Echogenic bowel
B: Thickened nuchal fold
Answer: B: Thickened nuchal fold 
Explanation: Prenatal USG markers of Down syndrome- Thickness of nuchal fold (75% sensitive) Absence of nasal bone (58% sensitive) cardiac abnormalities, duodenal atresia, shoened femur, shoened humerus, echogenic bowel