This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: congenital anomalies of kidney, Subject name: Pediatrics
A woman with no history of any prenatal care is going to deliver a baby. She has no history of amniotic rupture and ultrasound showed severe oligohydramnios. Which of the following conditions can be the cause of oligohydramnios? 
Select and explain. 
A. Renal agenesis, B. Anencephaly, C. Trisomy 18, D. Duodenal atresia
A: Renal agenesis
Answer: A: Renal agenesis 
Explanation: Oligohydramnios occurs due to congenital abnormalities of the fetal kidneys or genitourinary tract, such as renal agenesis or obstruction, that impede normal formation or excretion of fetal urine. Anencephaly, trisomy 18 and duodenal atresia causes polyhydramnios.