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
[{'content': "What is the purpose of using Hasse's formula in pregnancy? \nSelect and explain. \nA. Estimate fetal age, B. Identify fetal blood group, C. Identify fetal sex, D. Identify fetal congenital malformations", 'role': 'user'}, {'content': "Answer: A \nExplanation: Hasse's rule is employed in calculating the age of fetus by its length. During first five months of pregnancy, the length in cms is square of the age in months. During the second five months of pregnancy, length in cms divided by 5 gives age in months. Ref: Textbook of forensic medicine and toxicology by Krishan Vij, 3rd edition, Page 558.", 'role': 'assistant'}]