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': 'In pregnancy all occurs except: \nSelect and explain. \nA. Increased cardiac output, B. Decreased blood volume, C. Increased MCV, D. Increased glomerular flow', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Decreased blood volume', 'role': 'assistant'}]