This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Twin Pregnancy, Molar Pregnancy, Gestational Trophoblastic disease and contraception in special situations (Sour Grapes!), Subject name: Gynaecology & Obstetrics
[{'content': 'What is the most common type of conjoined twin? \nSelect and explain. \nA. Craniopagus, B. Thoracopagus, C. Ischiopagus, D. Pygopagus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Conjoined twins or Siamese twins are monozygotic twins, formed when the twinning of the embryo occurs after 12 days of feilization. Thoracopagus- fusion of thorax (most common type) Xiphopagusoromphalopagus- fusion of anterior abdominal wal Pygopagus- posterior fusion Ischiopagus - caudal fusion Craniopagus- fusion of cranium Rachipagus- dorsal fusion 6', 'role': 'assistant'}]