This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstetrics, Subject name: Gynaecology & Obstetrics
In which condition is this most likely to be seen? 
Select and explain. 
A. Trisomy 16, B. Monosomy X, C. Trisomy 21, D. Trisomy 13
C: Trisomy 21
Answer: C: Trisomy 21 
Explanation: USG showing Sandal Gap. There is an apparent increase in the inter space between the great toe of the foot from the rest of the toes (likened to the gap caused by a sandal). It is a soft tissue marker of Down's Syndrome.