Background: Decidua plays crucial regulatory roles in multiple biological processes. Previous studies have studied the function of decidua in isolated early or late pregnancy stages. Few studies focused on the changes in cell components and molecular function between the two stages.

Methods: Two datasets derived from decidua in the first and third trimester were obtained in the published database. We used Seurat, monocle2, and Cell Chat software to discuss the cell components and differences of expression profiles, cell subgroups, development, functions, and communication in three selected cell clusters between the two stages.

Results: we selected GSE186368 and E-MTAB-67013 as research objects. Single-cell transcriptome identified eight common clusters at the early or late pregnancy stages in normal decidual tissues. The results suggested that cell composition had apparent developmental specificity. For example, EC and EVT mainly originated from the late trimester stage. However, EEC and dNK could mainly be detected in the first-trimester stage. Functional analysis of the selected DSC, EVT, and FB suggested that they have different cell fates. Cell communication analysis indicated that dNK cells have the most active signal with other cell types in the first and late trimesters. OSR2, REN, and RGS5 were specifically expressed in the first trimester stages. 

Conclusions: This study is the first to describe the heterogeneity of decidual tissue at two developmental stages. OSR2, REN, and RGS5 could be potential markers of FB cells for molecular mechanisms study.