This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Volume of amniotic fluid needed for fetal karyotyping. 
Select and explain. 
A. 10 ML, B. 20 ML, C. 2 -3 ML, D. 3 - 5 ML
B: 20 ML
Answer: B: 20 ML 
Explanation: 20 ML of amniotic fluid is required for fetal karyotyping.
10 ML is required for FISH.