Connective tissue cells of the endometrium, these cells are fibroblastic in appearance. During decidualization they tranform into decidual (stromal) cells, swellling up and adopt an epithelial cell-like appearance due to the accumulation of glycogen and lipid droplets. [ http://www.ncbi.nlm.nih.gov/pubmed/11331626 http://www.ncbi.nlm.nih.gov/pubmed/30013421 Wiki:Decidualization&oldid=908981933#Endometrial_stromal_cells_(ESCs) ]