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': 'Related to calcium metabolism, which of the following does not occur during pregnancy \nSelect and explain. \nA. Total serum calcium levels fall., B. 80% of fetal calcium deposition occurs in third trimester., C. Fetal skeleton excretes approximately 30g of calcium by term., D. Serum ionized calcium levels fall.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Serum ionized calcium levels remain unchanged in pregnancy.', 'role': 'assistant'}]