This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis of Pregnancy, Subject name: Gynaecology & Obstetrics
WHICH SYNDROME IS MC ASSOCIATED WITH CYSTIC HYGROMA IN 1ST TRIMESTER USG 
Select and explain. 
A. Trisomy 21, B. Trisomy 18, C. Trisomy 13, D. Turner syndrome
A: Trisomy 21
Answer: A: Trisomy 21 
Explanation: When Cystic hygromas are diagnosed in the first trimester , Trisomy 21 is most common aneuploidy followed by Turner's syndrome and Trisomy 18