This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
USG at 28 weeks of gestation shows oligohydramnios is likely due to : 
Select and explain. 
A. Gastrointestinal obstruction, B. Renal pathway obstruction, C. Anencephaly, D. Neuromuscular disorder
B: Renal pathway obstruction
Answer: B: Renal pathway obstruction 
Explanation: Etiology of oligohydramnios: Intrauterine growth restriction Post-term pregnancy Premature rupture of membranes Drugs like ACE inhibitors and prostaglandin inhibitors Renal anomalies Renal Agenesis Infantile polycystic kidney disease urinary tract obstruction Ref: Sheila 2e pg 216.