The radioimmunoassay of placental protein 5 and circulating levels in maternal blood in the third trimester of normal pregnancy.

A radioimmunoassay has been developed for placental protein 5 (PP5), a product of the human placenta. Circulating concentrations of PP5 were measured in the third trimester of normal pregnancy in 400 women. Concentrations of PP5 showed a skewed distribution and rose progressively to reach a plateau in the last four weeks of pregnancy. The development of this assay will permit studies on the potential clinical application of maternal PP5 levels during normal and abnormal pregnancy.