Pre-eclampsia is proposed to progress in two stages. The first stage involves inadequate development of maternal spiral arteries resulting in deficiency in placental perfusion.
The second stage involves widespread endothelial dysfunction resulting in hypertension, proteinuria, and oedema. Foetal perfusion is supplied by the maternal blood supply through spiral arteries, which are terminal branches of radial arteries. In normal pregnancies, the spiral arteries are invaded by trophoblastic cells that replace the endothelium of these arteries and promote remodelling of the vascular wall with dilation of the blood vessels. In pre-eclampsia, the placental invasion of these arteries is insufficient, resulting in narrower blood vessels and hypoperfusion of the placenta