Revised estimates and projections of Down syndrome births in the United States, and the effects of prenatal diagnosis utilization, 1970-2002.

The objectives of this study were to: calculate revised estimates and projections of United States annual Down syndrome (DS) births for 1970-2002, and estimate the effects of amniocentesis on these baseline DS birth projections. Three models of amniocentesis utilization among 30-34 and greater than or equal to 35-year-old women were considered. The recently revised Census Bureau birth projections, and new single year maternal age DS risk rates estimated from a 1970-1983 Ohio data set, were used. Data from all three Census Bureau projection series were analysed; series II was considered in depth since it is consistent with recent fertility levels. Assuming no use of amniocentesis, total estimated DS births dropped from about 4770 in 1970 to 4120 in 1980 (a 14 per cent decline), but are projected to a plateau of about 5100 by the year 1990 (a 24 per cent increase). DS births to women greater than or equal to 35 would increase dramatically from about 1050 in 1980 to 1900 in 2000 (an 81 per cent increase). Assuming 1983 Ohio prenatal diagnosis ratios for women aged 30-34 (1.7 per cent) and greater than or equal to 35 (23.4 per cent) are used nationally, an annual reduction of about 7 per cent of DS births in 1986 and 9 per cent in 2002 would result. Fifty and 70 per cent utilization among women 30-34 and greater than or equal to 35, respectively, would reduce DS births by about 33 per cent in 1986 and 38 per cent in 2002. Therefore, if the projected increase in DS births is to be averted, utilization of prenatal diagnosis by greater than or equal to 30-year-old women must increase substantially.