Unveiling the emerging role of endometrial microbiota with the coordination of cytokines and growth factors at the maternal-fetal interface.

Early embryonic loss is a common issue in all mammalian species, particularly due to implantation failure. This is a significant concern not only for farmers but also for couples who experience infertility. Recurrent implantation failure (RIF) can be addressed by better understanding the key factors that influence embryo implantation. This review comprehensively elucidates the roles of essential factors, including cytokines, growth factors, and the endometrial microbiome, in the implantation process. Disruption of any of these factors can lead to implantation failure, which is a crucial determinant for a successful pregnancy. The maternal immune system must adapt to accept semi-allogenic embryos. The uterine environment becomes challenging to accept the embryo while combating foreign antigens. This requires changes in the physiology, immunology, and morphology of the endometrial tissue. The endometrial microbiome is emerging as a key contributor in modulating the maternal immune response, providing antibacterial metabolites, and creating an anaerobic environment that is favorable for the early embryo. Furthermore, cytokines and growth factors are widely recognized for their critical roles in embryo implantation. Supplementing these factors before natural breeding or artificial insemination has been shown to reduce reproductive complications, particularly embryo implantation failure.