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
[{'content': 'WHICH SYNDROME IS MC ASSOCIATED WITH CYSTIC HYGROMA IN 1ST TRIMESTER USG \nSelect and explain. \nA. Trisomy 21, B. Trisomy 18, C. Trisomy 13, D. Turner syndrome', 'role': 'user'}, {'content': "Answer: A \nExplanation: When Cystic hygromas are diagnosed in the first trimester , Trisomy 21 is most common aneuploidy followed by Turner's syndrome and Trisomy 18", 'role': 'assistant'}]