Projection of Down's syndrome births in the United States 1979-2000, and the potential effects of prenatal diagnosis.

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Abstract
This study projects the annual number of Down's syndrome (DS) births during 1979-2000 by maternal age categories, and estimates the effects of prenatal chromosomal diagnosis utilization on reducing these baseline projections. Assuming no reduction in DS births through prenatal diagnosis, projected DS births increase from about 4,300 in 1979 to 5,300 in 1990, where the level would remain approximately stable throughout the 1990s. Applying Ohio's 1980-1981 prenatal chromosomal diagnosis utilization ratio of 17 per cent to women greater than or equal to 35 results in a maximum of 6 per cent reduction in the annual baseline projections of DS births over the next two decades. However, if amniocentesis utilization by women age 30-34 increases to 37.5 per cent and to 75 per cent by women greater than or equal to 35, a one-fourth to one-third annual reduction is achieved throughout the period studied. A substantial increase in prenatal diagnosis appears necessary to offset the projected increase in DS births resulting from a larger number of births to women greater than or equal to 35.