A SENSITIVE ENZYME-IMMUNOASSAY FOR PREGNANCY-ASSOCIATED PLASMA-PROTEIN-A (PAPP-A) - A POSSIBLE FIRST TRIMESTER METHOD OF SCREENING FOR DOWN-SYNDROME AND OTHER TRISOMIES

Pregnancy-associated plasma protein A (PAPP-A) is a large glycoprotein produced mainly by the trophoblast during pregnancy and released into the maternal circulation. Its biological function is unknown. In the second trimester i.e. when Down syndrome (DS) screening is routinely p erformed, the level of maternal serum PAPP-A was found to be within th e normal range in pregnancies affected by fetal trisomy 21. However, P APP-A was shown to be a potent marker for DS before 14 weeks of gestat ion. Only radioimmunoassays (RIAs) based on labelled antigen competiti on reached the required sensitivity for early pregnancy PAPP-A determi nations; but they have a very short shelf life due to inherent tracer half-life and, in the case of PAPP-A, instability of the labelled anti gen after three weeks. We describe a convenient and novel enzyme immun oassay (ELISA) with high sensitivity and a long shelf life.