Circulating and tissue concentrations of pregnancy-associated plasma protein-A (PAPP-A) in tubal ectopic gestation

Concentrations of pregnancy-associated plasma protein-A (PAPP-A), human chorionic gonadotrophin (hCG) and pregnancy specific beta 1-glycoprotein (SP1) were measured by radioimmunoassay in 164 serum and 29 tissue samples obtained from 87 non-pregnant and 29 pregnant women with either tubal (n = 16) or intrauterine (n = 13) pregnancies. Of the 47 serum samples obtained from patients with a tubal pregnancy only two were positive for PAPP-A, whereas in excess of 94% of the samples were positive for both hCG and SP1. Serial measurements of hCG, and SP1, demonstrated an apparently normal growth rate for the tubally implanted trophoblast for the first 6 weeks of pregnancy. Thereafter, the tubal trophoblast is compromised since the tissue content of PAPP-A and hCG was significantly lower than that in intra-uterine derived trophoblastic tissue. By contrast, the content of both PAPP-A and hCG was significantly greater in the trophoblastic, both intra or extra-uterine derived, than in the endometrial/decidual, tissue. Furthermore, the absence of immunoreactive PAPP-A and the severely depressed circulating levels of PAPP-A in women with tubal pregnancies can be attributed to diminished secretion of PAPP-A into the maternal circulation. Therefore, in conjunction with a positive pregnancy test and the patient's clinical history, a severely depressed or absent serum PAPP-A level may aid in the diagnosis of extrauterine pregnancy.