Embryo-maternal cross-talk: key players in successful implantation and live birth rates

A successful pregnancy requires that the embryo and the endometrium undergo regulated alterations during the preimplantation phase, which can have positive effects on each other due to these adaptations. The focus of this review is to study the alterations in both the immune system and gene expression within the endometrium, along with exploring the embryonic surface and secretory markers crucial for successful implantation. Innate and adaptive immune cells in the endometrium phenotypically differ from immune cells in other human tissues. Research has demonstrated the significance of the communication network among these cells, as well as the involvement of cytokines and chemokines in the implantation process. In addition to immune cells, changes in endometrial gene expression, such as adhesion molecules, homeobox (HOX) genes, and progestagen-associated endometrial protein (PAEP), lead to developing a receptive endometrial phenotype. The embryo is another key actor in the implantation process, and its interaction with the endometrium relies on the expression of surface and secretory components before implantation. There are many surface factors, such as integrins, which contribute to establishing physical connections. In contrast, secretory factors, such as preimplantation factor (PIF) with paracrine and autocrine effects, are crucial in embryonic development and the preparation of the uterine environment.