This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Gynaecology & Obstetrics
Most accurate tool for gestational age assignment is 
Select and explain. 
A. Menstrual history, B. Clinical assessment, C. First trimester Crown-Rump length, D. Femur length
C: First trimester Crown-Rump length
Answer: C: First trimester Crown-Rump length 
Explanation: A first-trimester crown rump length is the most accurate tool for gestational age assignment and is performed as clinically indicated. (Ref: William's Obstetrics; 25th edition)