Spiral (uteroplacental) arteries of the human placental bed show the presence of amniotic basement membrane antigens

The spiral arteries of the placental bed lose clearly recognizable arterial features early in pregnancy because of their invasion by extravillous trophoblast. Extensive structural alterations take place in the walls of invaded arteries, their walls containing an amorphous acidophilic "fibrinoid" matrix in which endovascular trophoblast is embedded. Such spiral arteries examined by immunofluorescence techniques in placental bed biopsy specimens obtained at cesarean section show a characteristic pattern of reaction with antisera to epithelial basement membrane amniotic antigens. These antisera have been previously demonstrated to react with the basement membrane of human amnion and of ectodermally derived epithelium such as breast ducts and skin. Interstitial trophoblast usually does not contain these antigens, and it is postulated that, following vascular invasion, endovascular trophoblast produces amniotic antigens to establish its presence. This may be of importance in maintaining the structural integrity of spiral arteries and thereby adequate maternal blood flow to the fetal-placental unit.