MATERNAL SERUM ALPHA-FETOPROTEIN, AGE, AND DOWN-SYNDROME RISK

Before the discovery that an association existed between low maternal serum .alpha.-fetoprotein levels and Down syndrome, the ability to detect Down syndrome pregnancies was limited to women aged .gtoreq. 35, whose individual risks were sufficiently high (.gtoreq. 1: 270 in the second trimester) to justify offering amniocentesis. If such women were to opt for that procedure, about 20% of all cases of Down syndrome could be detected. It is now possible to identify an additional 20% of all Down syndrome pregnances in women under age 35, with the use of a screening process that combines a woman''s maternal serum .alpha.-fetoprotein level and her age. We present a method whereby a woman''s individual odds for Down syndrome can be calculated by combining the maternal serum .alpha.-fetoprotein measurement with her age, on the basis of published age-related Down syndrome risk data and on maternal serum .alpha.-fetoprotein distributions for unaffected and Down syndrome pregnancies. These individual odds calculations provide the basis both for establishing maternal serum .alpha.-fetoprotein/Down syndrome screening cutoffs and for counseling.