Physiological Angiogenesis in Implantation

This comprehensive review examines the intricate processes that guide embryo implantation, with particular emphasis on angiogenesis, vascular development, and the critical role of vascular endothelial growth factor (VEGF) in successful pregnancy. Vascular development, defined as the coordinated processes of vasculogenesis (de novo formation of blood vessels from endothelial progenitors) and angiogenesis (sprouting and remodeling of existing vessels), is identified as a fundamental prerequisite for establishing uterine receptivity. VEGF emerges as a key regulator that influences endothelial cell proliferation, migration, and vascular permeability; its dysregulation is associated with impaired endometrial receptivity and reduced implantation rates. In addition, the review considers hypoxia as a potent initiator of angiogenesis, emphasizing the hypoxia-inducible factor-1 (HIF-1) pathway in linking the hypoxic environment to gene activation required for new vessel formation. Collectively, the review underscores the interplay among vascular development, angiogenesis, VEGF, and hypoxia in determining the success of embryo implantation, thereby shaping pregnancy outcomes.