The placentae bed

Objectives: To review critically published data concerning fetal-maternal interaction at the placental bed level in normal and complicated pregnancies. Emphasis is placed on the adaptive changes of the uteroplacental vasculature of the placental bed. Methods: Histopathological and immunohistochemical data form the basis of this review. The relevance of recent studies on cultured trophoblast is considered in the light of histological findings. Results: The findings of recent experimental studies on invasive processes and trophoblast-extracellular matrix interaction relate mainly to interstitial trophoblast, since no in vitro model is available for the study of vascular changes. The endovascular pathway of vascular invasion is emphasized, and mechanisms of arterial wall destruction need to be reconsidered since vascular disorganization and disruption may precede trophoblast invasion. There is a need for blood flow studies in relation to histopathological findings. Currently the role of various cytokines in trophoblast-maternal interaction is being intensively investigated, since disturbances in the cytokine network may be responsible for the inhibition of trophoblast invasion in complicated pregnancies. Conclusions: Various new techniques have led to a better insight of trophoblast invasion and its regulation. It is important that these should be interpreted in the context of histological reality as observed in the placental bed.