Q: What is the risk of having another Down Syndrome baby?
A: Without taking maternal age into account, the chance of having another child with Down syndrome is about 1% in each subsequent pregnancy. Parents of children with translocations must have a chromosomal analysis to assess actual future risk. Translocations can be sporadic or inherited, and the recurrence risk for subsequent pregnancies can only be calculated when both parents have a karyotype done. The recurrence risk of Down syndrome depends on how the baby acquired the Down syndrome.
- If the father is a 'balanced translocation' carrier to another chromosome (usually 13, 14, 15, 22), then the recurrence risk is about 1 in 40.
- If either parent is a 'balanced translocation' carrier to chromosome 21 (21/21) then the recurrence risk is 100%.
- If the chromosomes of both parents are OK, then the recurrence risk is about 1% if the mother is under 40 years of age and about twice that for a mother who is 40 and over. [Selikowitz, M Down Syndrome: The facts, 2nd Ed., 1997, p. 177]