The development of assay systems for pregnancy specific [beta] 1 glycoprotein (SP1) and pregnancy associated plasma protein A (PAPP-A) and their clinical application in pregnancy

Pregnancy specific A 1 glycoprotein (SP1) was isolated by immunoadsorption techniques from late pregnancy serum and the purified protein utilised in the development of a sensitive radioimmunoassay. In addition SP1 levels were measured by the new technique of kinetic immunoturbidimetry. Different physico-chemical principles involved in the kinetic assay explained conflicting results obtained when comparing radioimmunoassay of SP1 with electroimmunoassay. The presence of more than one protein possessing SP, antigenic determinants in late pregnancy serum was confirmed and further information concerning the heterogeneity of SF1 was obtained. A radioimmunoassay was also developed for the measurement of pregnancy associated plasma protein A (PAPP A) and compared with that of SP. The assays of SP1 and PAPP-A were applied to clinical studies during pregnancy. Assay of SP, was shown to be useful for early detection of pregnancy. In subjects with threatened abortion between 7 and 14 weeks of gestation SP1 was found to be a good indicator of outcome with a predictive value, specificity and sensitivity of 97, 96 and 90 per cent respectively. Assay of PAPP-A was less effective than SP1 or human chorionic gonadotrophin (HCG) for predicting outcome. However, information was obtained on PAPP-A levels in the first trimester of pregnancy. It was also found that a glycoprotein such as SP, may be influenced by abnormal glucose tolerance during pregnancy. The advantages and disadvantages of different types of assay forSP1 and PAPP-A and the significance of clinical studies are discussed.