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 of the following is the most accurate way of dating the pregnancy? \nSelect and explain. \nA. Determination of uterine size on pelvic examination, B. Quantitative serum HCG level, C. Crown rump length on abdominal or vaginal ultrasound, D. Determination of progesterone level along with serum HCG level', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. is c, i.e. Crown rump length on abdominal or vaginal ultrasoundBest method for dating of pregnancy is ultrasound in first trimester. The best parameter is Crown Rump length.', 'role': 'assistant'}]