 Cellular infiltration is a key feature of immune function within decidua, and leukocytes comprise at least 40 of the total decidual stromal cell population11 . The leukocyte subtypes present include decidual uterine natural killer uNK cells, macrophage subtypes, CD4C and CD8C T-lymphocytes including T-regulatory cells Tregs and antigen-presenting cells APCs such as dendritic cells DCs12 . There has been renewed interest in the role vitamin D, as key regulators of decidual immune cell function and its roles in fetal-maternal immune tolerance 13 . 