A specific and highly sensitive radioimmunoassay for determination of pregnancy-associated plasma protein A in human serum is described. The minimum detection limit for this protein was 2.9 micrograms/L. The within- and between-assay coefficients of variation were 4.0 and 4.5%, respectively. The circulating protein was detected within 32 days of conception in eight normal pregnancies and within 21 days in a twin pregnancy. Circulating concentrations in the mother at term were consistently higher (10-fold) than in matched amniotic fluid; none was detected in the umbilical circulation. This protein was also detected in the circulation of patients with hydatiform mole. This assay will permit investigations into the clinical evaluation of measurements of the protein during early pregnancy and trophoblastic disease.

Maternal serum placental protein 12 (PP12) was measured at the time of presentation in 33 women with a histologically confirmed diagnosis of ectopic pregnancy [tubal pregnancy (n = 29), tubal pregnancy with a live fetus (n = 2), cornual pregnancy (n = 1) and ovarian pregnancy (n = 1)]. All but four of the 33 patients had PP12 measurements within the reference range. Two women had circulating PP12 levels above the 90th centile of the normal range, at 7 and 8 weeks gestation, respectively. One of these had a live ectopic gestation and the other patient conceived after in vitro fertilization. Two remaining patients (one each with a cornual and tubal pregnancy) at 11 and 12 weeks, respectively had levels below the 10th centile of the normal range. It is concluded that regardless of the implantation site, ectopic pregnancy is not associated with depressed maternal PP12 levels, suggesting that the decidual synthesis of this protein is independent of the intimate relationship between decidua and trophoblast.

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