This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Prenatal Diagnosis, Subject name: Gynaecology & Obstetrics
[{'content': 'Most impoant feature to diagnose fetal aneuploidy: \nSelect and explain. \nA. Absent nasal bone, B. Nuchal translucency, C. Increase in frontomaxillary angle, D. Reversal of ductus venosus flow', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Nuchal translucency evaluation represents the maximum thickness of the subcutaneous translucent area between the skin and soft tissue overlying the fetal spine at the back of the neck . It is measured in the sagittal plane between 11 and 14 weeks. When the nuchal translucency is increased, the risk for fetal aneuploidy and various structural anomalies--including hea defects--is significantly elevated.', 'role': 'assistant'}]