This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'Blighted ovum is: \nSelect and explain. \nA. Synaptic knobs, B. Avascular villi, C. Intervillous hemorrhage, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In missed aboion ultrasound will show a gestational sac smaller than expected with irregular and crenated margin. An embryonic pregnancy (blighted ovum )is considered when there is a gestational sac more than 16 mm in diameter without a foetal node.(refer pgno:146 sheila 2 nd edition)', 'role': 'assistant'}]