Transient loss of endothelial cells in human spiral artery remodelling during early pregnancy: Challenging the dogma

Spiral artery (SpA) remodelling is essential for a successful pregnancy and is best described by its morphological features; vascular smooth muscle cell separation and loss, vessel dilatation, and invasion by extravillous trophoblast cells (EVT). Current opinion holds that EVT fully replace the endothelial cells (EC) of the SpA and take on EC-like characteristics. Placental bed biopsies (6-20 weeks gestation) were immunostained for EC and EVT, showing transient loss of EC. In vessels containing an endovascular EVT plug (n = 28) 77.6 +/- 19.3% of the lumen was covered by EC while in vessels without endovascular EVT (n = 100) it was 100 +/- 0%.