Research advances in role of uterine natural killer cells in recurrent spontaneous abortion

According to the definition of the World Health Organization (WHO), recurrent spontaneous abortion refers to two or more successive pregnancy losses with the same spouse before 28 weeks of pregnancy. The etiology remains unknown in 40% to 60% of patients with recurrent miscarriage. During the proliferative phase of the endometrium, uterine natural killer cells account for approximately 30%-40% of the total immune cell population, and up to 70% during the secretory phase, playing a critical role in maintaining the immune microenvironment at the maternal fetal interface. This review describes how uterine natural killer cells participate in maintaining the immune balance at the maternal fetal interface during normal physiological pregnancy, including inducing local immune tolerance, promoting uterine vascular remodeling, and regulating trophoblast differentiation and invasion, summarizes the functional pathways of uterine natural killer cells in recurrent miscarriage from aspects such as receptor binding abnormalities, interference with uterine artery remodeling, and hormone regulatory axis abnormalities. These findings provide critical insights into elucidating the pathogenesis of recurrent miscarriage, advancing preventive strategies and therapeutic interventions, and ultimately improving clinical outcomes.