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': "Which of the following feature on second trimester ultrasound is not a marker of Down's syndrome: \nSelect and explain. \nA. Single umbilical aery, B. Choroids plexus cyst, C. Polycystic kidneys, D. Duodenal atresia", 'role': 'user'}, {'content': 'Answer: C \nExplanation: USG findings in downs syndrome are Intrauterine growth restriction Mild cerebral ventriculomegaly Choroid plexus cysts Increased nuchal fold thickness Cystic hygromas Diaphragmatic hernia Echogenic intracardiac foci Congenital hea defects Increased intestinal echogenicity Duodenal atresia ("double-bubble sign") Renal pelvis dilation Shoened humerus and femur Increased iliac wing angle Incurving (clinodactyly) and hypoplasia of the fifth finger Increased space between first and second toes: sandal gap Two-vessel umbilical cord(single Umblical aery)', 'role': 'assistant'}]