Histological Changes in the Cat Placenta Throughout Gestation.

This study on cat placental organogenesis provides a detailed histological description, emphasizing the stages that have been less described. Thirty-seven gestational sacs were obtained by ovariohysterectomy, and the gestational age of the embryos/fetuses was determined based on developmental characteristics. The placentas were measured and processed by routine histological techniques. Additionally, fresh tissue from a term placenta was processed for ultrastructural analysis. An in-depth histological analysis was performed, and several morphometric variables (placental and lamellar width, placental and labyrinthine thickness, area and number of decidual cells) were recorded and related mainly to gestational age. A significant increase was observed in fetal length from 31 dpc, while placental thickness rose until 39 dpc; lamellae became abundant, parallel, longer, and narrower. Many CTB cells gradually fused into the STB; however, it progressively reduced. Medium-sized decidual cells, arranged in groups at the junctional zone, were progressively incorporated into the lamellae; there, they persisted until term, decreasing in number and becoming larger and frequently binucleated. The description of temporal modifications in lamellar, trophoblastic, and decidual features widens current knowledge on feline placental morphogenesis. In addition, these findings might be valuable for elucidating mechanisms behind placental development, which in turn affect its efficiency.