Immunoassay: A New Basis for Gestational Down Syndrome Screening

(hCG) and hCG free b-subunit tests are used in combi-nation with unconjugated estriol and a-fetoprotein in the triple screen test, and with the addition of inhibin-A in the quadruple marker test for detecting Down syn-drome in the second trimester of pregnancy. These tests have a limited detection rate for Down syndrome:;40% for hCG or free b-subunit alone,;60 % for the triple screen test, and;70 % for the quadruple marker test, all at 5%, or a relatively high, false-positive rate. New tests are needed with higher detection and lower false rates. Hyperglycosylated hCG (also known as invasive tropho-blast antigen or ITA) is a new test. It specifically detects a unique oligosaccharide variant of hCG associated with Down syndrome pregnancies. We evaluated this new Down syndrome-directed test in prenatal diagnosis