This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
The best investigation for dating pregnancy Is : 
Select and explain. 
A. Crown rump length at 9 weeks, B. BPD at 18 weeks, C. Abdominal circumference at 24 weeks, D. BPD at 24 weeks
A: Crown rump length at 9 weeks
Answer: A: Crown rump length at 9 weeks 
Explanation: Crown rump length at 9 weeks