[Maternal recognition of pregnancy--comparative biology]

Despite of the rapid expansion experienced by the reproductive biotechnologies in last few years, their success still limited by the high rates of early embryonic death. Since continuos fetomaternal dialogue is a prerequisite of pregnancy in all mammals, during the past decade more emphasis have been devoted to understanding the cell biological processes that regulate embryo maternal communication. This review aims to highlight the unique features of pregnancy in the different mammalian species and outlines the uterine immunological response triggered by the oocyte upon fertilization as well as the mechanisims developed by the embryo in the different species to silence or byoass the maternal immune system, induce corpus luteum maintainance and maternal recognition of pregnancy.