*3.2.2 Trophoblast invasion*

Trophoblast invasion, into maternal spiral arteries, is an essential physiologic change that allows the anchoring of placenta to the decidua as well as the transplacental passage of nutrients and wastes between the mother and the fetus. Several studies in vitro [49] have shown that aPLs reduce the ability of extra-villous cytotrophoblast to invade the maternal decidua, so affecting both the anchorage of placenta and the spiral arteries transformation, the latter leading to a reduced blood flow to the placenta. The aPLs are thought to impaire trophoblast invasion by altering the expression of adhesion molecules such as placental growth factor (PIGF), vascular endothelial growth factor (VEGF) and soluble FmS-like kinase I (sFlt-I) as well as cytokines such as interleukin 1β [49, 52, 57]. Altered trophoblast invasion of leads to impaired transplacental passage resulting in pre-eclampsia and intrauterine growth restriction (IUGR). In fact, increased sFlt-I levels in the first trimester have been shown to correlate with later onset pre-eclampsia, suggesting them as predictors of preeclampsia [58].
