This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstetrics, Subject name: Gynaecology & Obstetrics
Most commonly detected genitourinary abnormality seen in first trimester ultrasound is ? 
Select and explain. 
A. Megacystis, B. Hydronephrosis, C. Cystic Kidney, D. Renal Agenesis
A: Megacystis
Answer: A: Megacystis 
Explanation: Most commonly detected genitourinary abnormality seen in first trimester ultrasound is megacystis. Megacystis is a sign of lower urinary tract obstruction , which have several causes. Fig1 - Megacystis in a male fetus at 13 weeks gestation Fig2 - Prune belly sequence by urethral obstruction sequence with megacystis