This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics And Genetic Disorders, Subject name: Pediatrics
Among the following, the most sensitive USG finding of Trisomy 21 is: 
Select and explain. 
A. Absent nasal bone, B. Thickened nuchal fold, C. Short femur, D. Echogenic bowel
B: Thickened nuchal fold
Answer: B: Thickened nuchal fold 
Explanation: b. Thickened nuchal fold(Ref: Textbook of Perinatal Medicine, 2nd Edition, edited by Asim Kurjak, Frank A. A. Chervenak, pg 835, Nelson's 20/e p 610-615)Prenatal USG markers of Down syndrome include thickness of nuchal fold (75% sensitive), absence of nasal bone (58% sensitive), cardiac abnormalities, duodenal atresia, shortened femur, shortened humerus, renal pyelectasis, a hyperechogenic bowel, and a choroid plexus cyst.