Comparative biology of the IGF system in endometrium, decidua, and placenta, and clinical implications for foetal growth and implantation disorders.

The insulin like growth factors and their binding proteins appear to play a central role during implantation and establishment of pregnancy in all species studied. Although there are similarities among species in the cell types that express IGFs and IGFBPs and their regulation during implantation and pregnancy, there are also significant differences. Understanding of the role of the IGF system in placental function in the human is of immense clinical importance, because serious complications of pregnancy such as intrauterine growth restriction and pre-eclampsia are thought to be associated with alterations in IGF system during early pregnancy and later in gestation. Research in laboratory and domestic animals, including transgenic and gene targeting studies in mice, has significantly improved our understanding of the role of IGF system in placental and foetal development. This paper reviews the diversity in the expression and regulation of IGF system in the decidua and placenta at the foetal-maternal interface in the human and different animal species, which may benefit in directing future studies in understanding of various complications of human pregnancy.