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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 concentration 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 peritoneal fluid. The day‐to‐day variation was small; the coefficient of variation at 38 weeks was only 7.3 per cent. After delivery, the concentration 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.

Summary Five different products secreted by the fetoplacental unit into the maternal circulation were measured in 272 patients when they were 34 weeks pregnant. The most useful indicator of present pathology or future complications of pregnancy was a placental protein, pregnancy associated plasma protein A which was raised in pre‐eclamptic toxaemia, antepartum haemorrhage and premature labour. The highest values were recorded in pre‐eclampsia before any signs of the disease were evident. Schwangerschafts protein 1 was also raised in pre‐eclampsia and antepartum haemorrhage but only after the disease had presented. Placental lactogen was also raised in pre‐eclampsia and its measurement may have some predictive value. Total oestriol was lowered in fetal growth retardation and the unconjugated steroid raised in pre‐eclampsia and lowered in retarded fetal growth.

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