Mr. and Mrs. Annadural have a 2 month old baby suffering with down's syndrome. Karyotype of Mrs. Annadural shows translocation variety of Down syndrome. Which of the following investigation will you advise to the parents before the next pregnancy?

When a pregnant woman has a history of previous child with Down syndrome, it becomes important to know the type of chromosomal constitution, not only in that particular child but also in the parents because the risk of recurrence in future pregnancy depends on all these factors (as shown in Table in Ans. 1). Karyotyping of Mrs. Annadural has already been done and a translocation variety of Down’s detected. Risk of recurrence however does not depend on mother’s karyotype alone, but it also depends on the father’s karyotype. Father’s karyotyping is therefore the test of choice prior to next pregnancy to determine the risk of recurrence.