<prompt> Among the following, the most sensitive USG finding of Trisomy 21 is:Absent nasal boneThickened nuchal foldShort femurEchogenic bowel  <response>: b. Thickened nuchal foldRef: Textbook of Perinatal Medicine, 2nd Edition, edited by Asim Kurjak, Frank A. A. Chervenak, pg 835, Nelsons 20e p 610-615Prenatal 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. 