Atherosis revisited: Current concepts on the pathophysiology of implantation site disorders

There are two distinct histological manifestations of impaired placental implantation in humans-incomplete trophoblastic vascular invasion and atherosis. Both have been described to occur in pregnancies affected by a variety of disorders such as preeclampsia, fetal growth restriction, systemic lupus erythematosus, and diabetes. Our purpose was to integrate recent developments in the understanding of implantation site disorders into a pathophysiological scenario that interrelates these placentation disorders and associated pregnancy complications. Sources were identified from a MEDLINE search of English-language articles published from 1966 to 1997. Additional sources were identified from references cited in relevant reports. We selected articles relating to the following topics: atherosis, implantation site disorders, trophoblastic invasion, preeclampsia, fetal growth restriction, implantation site development, atherosclerosis, and endothelial activation-damage. A contemporary version of normal placentation, including vascular adaptation, was reviewed with comments on normal trophoblastic differentiation and vascular invasion. Specific abnormalities of the implantation site, including atherosis and incomplete trophoblastic invasion, were discussed in the context of placental site hypoperfusion and the association with pregnancy complications. It was concluded that atherosis and incomplete trophoblastic invasion may be both a consequence and a cause of placental site hypoperfusion resulting in the development of preeclampsia and a variety of other pregnancy disorders.