An apparatus for determining if a pregnant woman is at significant risk of carrying a fetus with Down syndrome. The pregnant woman's maternal blood levels of the free beta subunit of human chorionic gonadotropin are measured. The level of free beta subunit of human chorionic gonadotropin individually or with other markers may be compared to reference data. A computerized apparatus for making the determination preferably using a probability density function generated from a set of reference data by a linear discriminant analysis procedure is disclosed. <IMAGE>
