*7.1.1 First phase: abnormal placentation and placental ischemia*

The placenta plays a pivotal role in the development of preeclampsia since it only develops in its presence and symptoms rapidly remit after delivery.

During the development of normal placentation, the cytotrophoblast invades the spiral arteries which leads to their remodeling; they will have low resistance and high elasticity or capacitance. This cytotrophoblastic vascular invasion not only affects the most superficial layers but reaches the muscle tunica. Trophoblast penetration has also been reported as incomplete and is not invasive in patients with preeclampsia; after complete remodeling of the spiral arteries, placental perfusion decreases. Although remodeling of the spiral arteries begins in the first trimester, it is not considered complete until weeks 18–20 of gestation.

Recently, great importance has been attributed to angiogenesis because of molecules such as VEGF, angiopectin, and other proteins in the ephrin family. The invasive trophoblast expresses VEGF, P1GF, VEGF, and their respective receptors. Likewise, in in vitro studies in which these signals were blocked, integrin alpha-1, a marker of pseudovasculogenesis, decreased alarmingly.
