After having one child with Down syndrome what is the likelihood of having another child with Down syndrome?

After having one child with Down Syndrome, the likelihood of having another is about one percent. If the first child's Down Syndrome is due to translocation trisomy 21, the likelihood of another Down Syndrome child increases. As far as researchers know at this point, Down Syndrome is not attributed to the parents' behavior prior and/or during pregnancy or any environmental factors. The incidence of Down Syndrome does rise if the mother is older than 35, but it does not account for a large number of Down Syndrome children. Since more women are having children at ages younger than 35, then number of babies born with the syndrome is higher in younger age groups.