Human Placental growth factor is encoded by PGF gene. Placental growth factor belongs to the VEGF (vascular endothelial growth factor) sub family and is the second member of the family.  The name is referred to placenta as it was cloned from the library of human placenta c DNA. It plays a major role in angiogenesis, vasculogenesis and embryogenesis. Placental trophoblast is the main source of Placental Growth Factor in pregnancy. Other tissues also express placental growth factor. Altered levels of placental growth factor levels is observed in the serum of women with preeclampsia. The late and early onset of preeclampsia in maternal serum shows sFlt-1 in higher levels and placental growth factor in lower levels. Gene inactivation studies in mice have shown that loss of placental growth factor does not affect reproduction and development or post natal life. But the mice showed impaired arteriogenesis and angiogenesis which leads to formation of tumour and ischemia in conditions with increased vascular endothelial growth factor A. angiogenesis is a crucial phenomenon for embryonic development and post-natal growth.

Similar to the other VEGF family, four isoforms of placental growth factor are known. Placental Growth factor 1 to 4 with 131, 152, 203 and 224 amino acids after signal peptide removal respectively. The difference between the isoforms is that PIGF-1 and PIGF-3 are diffusible isoforms and non-heparin binding whereas the PIGF-2 and PIGF-4 contain heparin binding domains. Placental growth factor is secreted in the form of glycosylated homodimer. Placental growth factor is widely expressed in the placenta throughout the gestation period and early embryonic development. Recently two important functions of placental growth factor have been researched. First involves the polarization status of tumor-associated macrophages and the second in the response which is necessary for adaptive cardiac remodelling during transverse aortic constriction.