Mr.and Mrs. Annadurai have a two month old baby suffering with Down's syndrome.Karyotype of Mrs.Annadurai shows translocation variety of Down syndrome.Which of the following investigations will you advise to the parents before the next pregnancy?

• A. Alpha-fetoprotein
• B. Triple test
• C. Beta-human chorionic gonadotropin(hCG)
• D. Karyotyping