Elevated levels of Inhibin-A in maternal serum or plasma have been shown to indicate the presence of Down's Syndrome. The assay method comprises the use of a monoclonal antibody specific for at least part of the Inhibin-A beta sub-unit ( beta A), and another monoclonal antibody specific for at least part of the Inhibin-A alpha sub-unit. The beta A antibody is used to capture Inhibin-A from the test sample, and the alpha sub-unit antibody is used as the detection antibody and is linked to a detectable marker. The method is carried out in the first or second trimester as a screening test to select patients for subsequent diagnostic testing.
