[An ultrafine structural investigation of the placental basal plate]

An optical and electron microscopy evaluation of implantation sites of 7-9 week pregnancies was performed. The area of investigation was the basal plate and tissues extending both maternally and fetally. The progressive development of villous trophoblasts to cytotrophoblasts in the cell column to syncytiotrophoblasts, to free or "invasive" trophoblasts, and their relationships to the decidua and myometrium were studied. In the fibrinoid layer located between the maternal and fetal tissues are found trophoblasts with amoeboid extensions as well as those showing signs of degeneration. Also found are inflammatory cells of maternal origin and cellular debris. Deep in the fibrinoid layer, in the decidua, there are well developed round trophoblasts as well as some which invade the vascular lumens and replace the endothelial linings. Some of these invasive trophoblasts become polynuclear giant cells. These findings suggest that cytotrophoblasts which form the placental villi also actively invade maternal tissues, eliciting maternal immunologic responses, which result in the development of the fibrinoid layer or "Battle Zone", between the maternal and fetal tissues.