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Background. Pregnant endometrial stroma, an immunologically privileged site in the female reproductive system, is enriched by decidual and natural killer (NK) cells. Since the cellular microenvironment in early pregnancy from the decidual tissues of normal and miscarriage cases has gained importance, with special emphasis on cell-to-cell contacts, we aimed to document the plastic structure of the cellular milieu in normal and miscarriage decidua. Methods. Endometrial biopsies were obtained from women after legal curettage or women who had been treated by curettage after miscarriage. Samples were analysed in a light microscope (LM), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Results. Decidual cells possess several polyploidic protrusions on cell membranes. NK cells were distributed among decidual cells. Decidual cells were found to develop gap junctions in the interfaces between each other. Their cytoplasms were also found to possess well-developed protein synthesising organelles. Decidual cells obtained from miscarriages showed a moderate degree of degeneration and, in between, a decreased number of junctional complexes. Mononuclear cell infiltration was found to be significantly low. Conclusion. We conclude that decidual cells during early pregnancy build a series of miniature cell-cell contacts to assemble a proper endometrial milieu. In contrast, in miscarriage samples, those intercellular communications seem lacking, associated with an increased number of NK cells, a phenomenon which obviously alters proper implantation and leads to the induction of embryonic disgenesis and miscarriage. [ABSTRACT FROM AUTHOR]