A woman with a baby of downs syndrome comes for preconceptional counseling. Karyotype of the affected baby shows nondisjunction. What is the chance of downs syndrome in the subsequent Pregnancy?

Recurrence RiskWith nondisjunction Down syndrome, the risk in a subsequent pregnancy would be 1% or the maternal age-related risk, whichever is higher. But in translocation Down syndrome, either parent may have translocation. In such cases, the risk to the offspring is 12% if the mother is the carrier and 3% if the father is the carrier. However, in the rare case of a carrier of a 21:21 translocation, the recurrence risk is 100%.Reference: Textbook of Obstetrics; Chapter 56; Prenatal diagnosis