PGF and preeclampsia: Restricted syncytial fusion also causes the outer syncytiotrophoblast to reorganize into syncytial knots,23 which become the principal sites of aberrant sFlt1 production.24 Explanted placental villi derived from pregnancies with preeclampsia with severe features condition their cultured media to show a high sFlt1/PlGF ratio, and this media is rendered highly anti-angiogenic in vitro.