Placental growth factor is a protein that in humans is encoded by the PGF gene. It is a secreted protein and belongs to the PDGF/VEGF growth factor family. The protein is a member of the VEGF (vascular endothelial growth factor) sub-family-a key molecule in angiogenesis and vasculogenesis, in particular during embryogenesis. The main source of PGF during pregnancy is the placental trophoblast. PGF is also expressed in many other tissues, including the villous trophoblast.