Epidemiology
The CDC estimates that about 1 of every 691 babies born in the United States each year is born with Down syndrome. Each year about 6,000 babies in the United States are born with this condition. Approximately 95% of these are trisomy 21.
Maternal age influences the chances of conceiving a baby with Down syndrome. At maternal age 20 to 24, the probability is one in 1562; at age 35 to 39 the probability is one in 214, and above age 45 the probability is one in 19. Although the probability increases with maternal age, 80% of children with Down syndrome are born to women under the age of 35, reflecting the overall fertility of that age group. Recent data also suggest that paternal age, especially beyond 42, also increases the risk of Down syndrome manifesting.
Read more about this topic: Down Syndrome