Figure 1

Placental anatomy and trophoblast subtypes at early and mid-gestation. A, B. Embryonic day 8.5 implantation site. A – The collapse of the ectoplacental cone cavity (~E8.0) brings the base of the ectoplacental cone into contact with the distal surface of the chorion, while the allantois makes contact with, and adheres to, the basal surface of the chorion by E8.5. B – Large parietal TGC cells line the implantationsite. C-H. Embryonic day 14.5 placenta. C – Spiral artery lined by spiral artery TGCs. D – parietal TGC with glycogen trophoblast cells located beneath within the spongiotrophoblast layer as well as glycogen trophoblast cells which have invaded above the parietal TGC layer into the decidua. E – Clusters of glycogen trophoblast cells within the spongiotrophoblastlayer. F – Large central canal lined by canal TGCs. G – The maternal blood sinuses and fetal blood vessels (lined by endothelial cells) of the labyrinth are separated by a trilaminar trophoblast layer; sinusoidal TGCs that line the maternal sinusoids and two layers of syncytiotrophoblast. H – Clusters of glycogen trophoblast cells invade into the decidua beginning on E12.5. Ch – chorion, C-TGC – canal trophoblast giant cell, Dec – decidua, EPC – ectoplacental cone, Endo – endothelial cell, GlyT – glycogen trophoblast cell, P-TGC – parietal trophoblast giant cell, S-TGC – sinusoidal trophoblast giant cell, SpA-TGC – spiral-associated trophoblast giant cell, SpT – spongiotrophoblast, SynT – syncytiotrophoblast cell (I – layer I, II- layer II). Black bar represents 0.1 mm.