Fig. 1.

Schematic diagram of the two-stage theory of preeclampsia. In normal pregnancy, appropriate EVT invasion into the maternal endometrium (red arrow) leads to sufficient maternal blood flow from the spiral artery (A). PlGF, which is secreted from the placenta, activates VEGF and maintains a healthy endothelium (B). On the other hand, in preeclamptic pregnancy, incomplete invasion of the EVT (blue arrow) leads to insufficient maternal blood flow from the spiral artery and subsequent placental hypoxia (C). sFlt1 is then secreted from the placenta, which suppresses VEGF, resulting in systemic endothelial dysfunction and the appearance of various clinical symptoms (D). HELLP syn. hemolysis, elevated liver enzymes, low platelet count syndrome, FGR fetal growth restriction, NK cells natural killer cells, EVT extravillous trophoblast, PlGF placental growth factor, sFlt1 soluble fms-like tyrosine kinase-1, VEGF vascular endothelial growth factor