Oligohydramnios is associated with: (A) Renal agenesis, (B) Neural tube defects, (C) Postmature birth, (D) Premature birth
Answer is A. Etiology of oligohydramnios: 

Intrauterine growth restriction
Post-term pregnancy 
Premature rupture of membrane 
Drugs like ACE inhibitors and prostaglandin inhibitors 
Renal anomalies 
Renal Agenesis 
Infantile polycystic disease 
Upper urinary tract obstructions 
Lower urinary tract obstructions