MATERNAL AGE-SPECIFIC RISK RATE ESTIMATES FOR DOWN-SYNDROME AMONG LIVE BIRTHS IN WHITES AND OTHER RACES FROM OHIO AND METROPOLITAN ATLANTA,1970-1989

Our primary objective was to estimate, by one year and five year inter vals, maternal age specific risk rates for Down syndrome among whites and among other rates from two different populations, metropolitan Atl anta and south west Ohio, using Live birth and prenatally diagnosed ca ses ascertained during 1970-1989., The five year estimates were also c alculated separately for each of the five four year periods during the se 20 years. Additionally, we compared two different methods of estima ting these risk rates by using a third population of whites, and compa red two different statistical methods of smoothing the risk rates. The results indicate good agreement between the metropolitan Atlanta and south west Ohio estimates within races, but show a statistically signi ficant difference between the two race categories. Because 86% of live : births in the ''other races'' category in the combined population ar e to blacks, these data may be seen as the first estimates of maternal age specific risk rates for Down syndrome among blacks calculated by one year intervals. We found excellent agreement in the risk rate esti mates among the five four year time periods, between the estimates obt ained by using the two different methods of estimation, and between th e estimates obtained using the two different methods of statistical sm oothing. Our estimated risk Fates for white women in their 20s strongl y reinforce those from previous studies currently being used for genet ic counselling purposes. While we did find somewhat higher rates for w omen under 20, and increasingly higher rates for those over 30 years o f age, these differences are not substantial. Thus, this study in gene ral supports the risk rates estimated from data collected mostly durin g the 1960s and 1970s.