Figure 1.

A schematic of the process of spiral artery remodelling. Prior to trophoblast mediated remodelling the spiral arteries are small tortuous vessels. Invasive extravillous trophoblasts invade both into the maternal decidua and the lumen of the spiral arteries in the first trimester of pregnancy. The endovascular trophoblast initially plugs the lumen of the spiral arteries, preventing high-velocity blood flow to the placental surface in the first trimester. Ultimately, the spiral arteries are remodelled into large ‘funnel-like’ openings and can accommodate a high flow volume of maternal blood without excessive velocity. (Online version in colour.)