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': 'Which among the following is the commonest site of ectopic pregnancy? \nSelect and explain. \nA. Uterus, B. Cervix, C. Abdomen, D. Tubes', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Nearly 95 percent of ectopic pregnancies are implanted in the various segments of the fallopian tubes. Of these, most are ampullary implantations, followed by the isthmus. The remaining 5 percent implant in the ovary, peritoneal cavity, or within the cervix. Because the tube lacks a submucosal layer, the feilized ovum promptly burrows through the epithelium, and the zygote comes to lie near or within the muscularis. The rapidly proliferating trophoblast may invade the subjacent muscularis. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 10. Ectopic Pregnancy. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.', 'role': 'assistant'}]