The human placental bed revisited.

Pre-eclampsia, fetal growth restriction and spontaneous miscarriage have all been linked to abnormalities in trophoblast invasion into the placental bed. Despite intensive research our understanding of the mechanisms that control human trophoblast invasion in normal, let alone abnormal pregnancy, are still poorly understood. This is partly due to difficulties in obtaining "true" placental bed biopsies and most investigators have relied on in vitro models to try and understand the processes which control trophoblast invasion. The purpose of this article is to review the various studies which have attempted to sample the placental bed along with their success rate in doing so and secondly to review our current understanding of the morphological changes which occur in the placental bed in normal pregnancy, pre-eclampsia and spontaneous miscarriage.