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
A pregnant female, 38 years old, had a child with Down's syndrome. How do you assess the risk of Down's syndrome in the present pregnancy: 
Select and explain. 
A. Material alpha-feto protein, B. Material HCG, C. USG, D. Chorionic villous biopsy
D: Chorionic villous biopsy
Answer: D: Chorionic villous biopsy 
Explanation: In patients with previous history of Down syndrome
“The risk of recurrence is greater than the risk of genetic diagnosis and these patients should be advised to seek genetic counselling and to have a genetic diagnosis.”
Fernando Arias 3/e, p 27
Therefore amniocentesis /Chorionic villous biopsy should be done.