Comparative epidemiology of Down syndrome in two United States population, 1970-1989.

This study compared the epidemiology of Down syndrome over a 20-year period, 1970-1989, in two populations in which livebirths with Down syndrome were believed to be highly ascertained. One population was a 10-county region in southwest Ohio; the second was a five-county region in metropolitan Atlanta, Georgia. The major objectives were to 1) compare observed incidences of Down syndrome over the entire study period; 2) calculate expected incidences of Down syndrome for each population and compare these with observed incidences; 3) determine incidence trends throughout the period; and 4) examine the impact of prenatal diagnosis on the observed incidence of Down syndrome in each population.