Enzyme immunoassay for pregnancy-associated plasma protein-A.

This enzyme immunoassay procedure for pregnancy-associated plasma protein type A involves a "sandwich"-type system in microtitration plates. One can detect 0.27 mg of the protein per liter of serum, with a between-batch CV of 10.2%, and the antiserum used does not cross react with any of the other placentally derived proteins. A reference interval for the last trimester of pregnancy is presented. The procedure described is suitable for studying the behavior of this protein during pregnancy.