El-Azzamy H, et al. - Researchers performed this study on women with recurrent pregnancy losses (RPL), to determine the vascular development and density of uterine NK (uNK) cells in secretory endometrium of these subjects given the importance of uNK cells in pregnancy establishment. Fertile controls (n = 7) were also included. In all participants, mid-secretory phase endometrial tissues were investigated. They used immunohistochemistry and western blot to determine vascular smooth muscle cells (VSMC) expressing smooth muscle myosin (SMM). They found women with RPL vs controls had increased uNK cells in mid-secretory endometrium, which were related to increased vascularization and defective vascular transformation of spiral arteries in these subjects.