Maternal recognition of pregnancy

Maternal recognition of pregnancy requires signaling between the conceptus (embryo and its associated membranes) and the maternal system for maintenance of the corpus luteum (CL). Progesterone, produced by the CL, is required for regulation of endometrial functions that support early embryonic development, implantation, placentation, and fetal/placental development.1,2 Pregnancy recognition signals can be luteotropic, luteal protective, or antiluteolytic. Luteotropic signals include chorionic gonadotropin (CG), produced by human and primate conceptuses, which acts directly on CL via luteinizing hormone/chorionic gonadotropin receptor (LHCGR) to insure CL maintenance. The ovarian cycle of primates is independent of the uterus, as regression of the CL results from intraovarian effects of prostaglandins, oxytocin, or other undefined luteolytic agents. Therefore, it follows that CG acts directly on the CL to abrogate the intraovarian luteolytic mechanism.3.