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: Surgery
[{'content': 'An obstetrician sees a pregnant patient who was exposed to rubella virus in the eighteenth week of pregnancy. She does not remember getting a rubella vaccination. The best immediate course of action is to \nSelect and explain. \nA. Terminate the pregnancy, B. Order a rubella antibody titer to determine immune status, C. Reassure the patient because rubella is not a problem until after the thiieth week, D. Administer rubella immune globulin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The highest risk of fetal infection with rubella occurs during the first trimester. In seronegative patients, the risk of infection exceeds 90%. However, before other measures (such as termination of pregnancy) are considered, a rubella immune status must be performed. A rubella titer of 1:10 is protective.', 'role': 'assistant'}]