British Journal of Obstetrics and Gynaecology zyxwvuts November 1979. Vol. 86. pp zyxwvut 882-887 STUDIES ON PREGNANCY-ASSOCIATED PLASMA PROTEIN A IN THE THIRD TRIMESTER zyxw OF PREGNANCY BY R. SMITH*, MRC Research Fellow P. BISCHOF, Research Biochemist G. HUGHES, Senior Registrar AND A. KLOPPER, Professor zyxwv of Reproductive Endocrinology Depurtment zyxwvuts of Obstetrics and Gynaecology, University of Aberdeen Aberdeen, AB9 2ZB Summary The plasma concentration of pregnancy-associated plasma protein A (PAPP-A) was measured in 34 women during the last 10 weeks of pregnancy. From 30 to 36 weeks the concentration of this protein increased steadily. Thereafter the concen- tration of PAPP-A rose more steeply, the highest amounts being found in early labour. The concentration of PAPP-A in peripheral venous blood and in the uterine vein was much the same. It was less in the retroplacental blood and a great deal less in the peritonea1 fluid. The day-to-day variation was small; the co- efficient of variation at 38 weeks was only 7 s 3 per cent. After delivery, the concen- tration of PAPP-A fell more slowly than other placental proteins and steroids, the average half-life being 51 hours. Although there is no doubt that PAPP-A is a product of the syncytiotrophoblast, our findings suggest that it is not simply secreted by the chorionic villi directly into the intervillous space but makes its way into the maternal circulation by a more circuitous route. PREGNANCY associated plasma protein A (PAPP-A) is a protein produced by the placenta and secreted into the maternal blood stream in increasing amount as pregnancy advances. It was first isolated five years ago (Lin et al, 1974a). Until now almost all the work on this protein has been done by this Miami team. They found that it was a relatively large molecule (750000 daltons) and, by immunofluorescent staining, showed that it was present in the syncytio- trophoblast. The first investigations (Lin and Halbert, 1976) have shown that the concen- zyxwv * Present address: Department of Obstetrics and Gynae- cology, Ninewells Hospital,Dundee. tration of PAPP-A alters in some obstetric dis- eases. This raises the possibility that measure- ments of PAPP-A might give an indication of the placental state. In order to explore the changes in disease it is necessary to have a clear picture of the variations which might be encountered in normal pregnancy. We have therefore set out to expand the data on PAPP-A in normal preg- nancy. To do so we have measured levels in a cohort of women serially during the last ten weeks of pregnancy. We have also determined the variation from day to day in the same subject and have measured the rate of decline in the plasma concentration after delivery of fetus and placenta. We have traced the spread of the 882