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
All of the following are commonly used for estimation of gestational age in mid trimester EXCEPT: March 2013 
Select and explain. 
A. Biparietal diameter, B. Crown Rump Length, C. Abdominal circumference of fetus, D. Femur length
B: Crown Rump Length
Answer: B: Crown Rump Length 
Explanation: Ans. B i.e. Crown Rump Length CRL is most accurate with an error of 2.1 days in the first trimester BPD, FL, HC (head circumference) & AC is commonly used for dating thereafter.