A) AM expression is regulated by estrogen (E2), progesterone, and hypoxia inducible factor 1α (HIF-1a). At the pre-implantation stage, AM is expressed by both the trophectoderm cells and the luminal epithelium, promoting uterine receptivity. The maternal components are colored blue and red while the fetal components are depicted in green and gray. B) At the site of implantation, AM continues to be expressed from the trophectoderm cells and from the luminal epithelium, which is important for successful implantation. C) In the developed placenta, AM is most highly expressed by trophoblast giant cells (mice) or extravillous cytotrophoblasts (humans) and may contribute to the maintenance of placental vascular tone. For both B and C, maternal components are colored blue and red and the fetal components are depicted in green and yellow.