Pregnancy-associated glycoproteins （PAGs） belonging to the multigene family encoded by the aspartic protease gene, are a group of specific glycoproteins synthesized and secreted by placental trophoblast giant cells of artiodactyls, which can be detected in the maternal circulation after embryo attachment. It has the potential to serve multiple functions, including embryonic attachment, placental development, pregnancy maintenance, embryo survival, proteolytic activity, and immune regulation, which are most often used as biomarkers for early pregnancy diagnosis and assessment of embryo loss, as well as indicators of evaluation of fetal viability and monitoring placental health.