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
Most impoant feature to diagnose fetal aneuploidy: 
Select and explain. 
A. Absent nasal bone, B. Nuchal translucency, C. Increase in frontomaxillary angle, D. Reversal of ductus venosus flow
B: Nuchal translucency
Answer: B: Nuchal translucency 
Explanation: 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.