The immunoregulatory role of progesterone during embryo implantation and pregnancy

: Progesterone (P4), the 'pregnancy hormone', plays a pivotal role in the establishment and maintenance of pregnancy by modulating maternal immune responses, thereby promoting immune tolerance toward the semi-allogeneic fetus. In this review, we examine the key pathways through which P4 mediates its effects on maternal immune systems. We elucidate P4's immunomodulatory functions, with a focus on how altered P4 signaling may affect immune tolerance toward the fetus and contribute to the pathogenesis of pregnancy complications. We further discuss the potential role of P4 supplementation in improving embryo implantation and preventing miscarriage, as well as its role in modulating immune-mediated pathological conditions during pregnancy, while emphasizing unresolved questions and directions for future investigation.