Significance and value of immunohistochemical localization of pregnancy specific proteins in feto-maternal tissue throughout pregnancy.

Tissue from 50 cases of products of conception and placenta at different gestational ages from as early as 12 d post ovulation up to 40 wk were examined by immunoperoxidase technique for localization of HCG, HPL, SP1, and PAPP-A. HCG was localized in the cytoplasm of syncytiotrophoblast (ST) with strong intensity in the 12-d blastocyst and remained strong until 8 to 10 wk. It then gradually decreased, becoming almost negative in term placenta. HCG was also seen in the cytoplasm of intermediate trophoblast (IT) at the implantation site but with variability in staining. HPL and SP1 appeared later than HCG in ST, and the intensity of staining increased rapidly to strongly positive by wk 8. They remained strong until full term. IT stained strongly positive with HPL throughout pregnancy, and some were different from the HCG positive ones. ST were constantly negative for PAPP-A throughout pregnancy. The latter, however, was definitely seen in the cytoplasm of cytotrophoblast (CT) of early blastocyst, the superficial epithelium of the endometrium adjacent to the implantation site, in many decidual cells around the implantation site and in the amniotic membrane epithelium.