This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Amniotic Fluid Dynamics, Subject name: Gynaecology & Obstetrics
A 19-year-old woman, gravida 2, para 0, aboion 1, is at 30 weeks gestation. Her fundal height measures 25cm. An obstetrical ultrasound examination reveals a 4 quadrant amniotic fluid index (AFI) of 4cm. Which of the following fetal conditions is associated with finding? 
Select and explain. 
A. Duodenal atresia, B. Open spina bifida, C. Tracheoesophageal fistula, D. Renal agenesis
D: Renal agenesis
Answer: D: Renal agenesis 
Explanation: - AFI <4 cm is suggestive of Oligohydramnios - The only option of the provided that leads to oligohydramnios is Renal agenesis. Oligohydramnios can be caused by - Renal anomalies Uteroplacental insufficiency: IUGR ACE inhibitors Premature rupture of membranes Amniocentesis (leak) Pre-ecclampsia Amnion nodosum NSAIDs Post term pregnancy over estimated gestational age