Human placental growth hormone in normal and abnormal fetal growth

Human placental growth hormone (PGH), encoded by the growth hormone (GH) variant gene on chromosome 17, is expressed in the syncytiotrophoblast and extravillous cytotrophoblast layers of the human placenta. Its maternal serum levels increase throughout pregnancy, and gradually replaces the pulsatile secreted pituitary GH. PGH is also detectable in cord blood and in the amniotic fluid. This placental-origin hormone stimulates glyconeogenesis, lipolysis and anabolism in maternal organs, and influences fetal growth, placental development and maternal adaptation to pregnancy. The majority of these actions are performed indirectly by regulating maternal insulin-like growth factor-I levels, while the extravillous trophoblast involvement indicates a direct effect on placental development, as it stimulates trophoblast invasiveness and function via a potential combination of autocrine and paracrine mechanisms. The current review focuses on the role of PGH in fetal growth. In addition, the association of PGH alterations in maternal circulation and placental expression in pregnancy complications associated with abnormal fetal growth is briefly reviewed.