Sun T, Gonzalez TL, Deng N, et al. - Since sexually dimorphic signaling at early stages of placentation are not defined, researchers sought to examine the effect of fetal sex on maternal-fetal crosstalk. Receptors/ligands at the maternal-fetal surface have been identified from sexually dimorphic genes between fetal sexes in the first-trimester placenta and defined in each cell type using single cell RNA-Sequencing (scRNA-Seq). Ninety-one sexually dimorphic receptor-ligand pairs were identified across the maternal-fetal interface. Fetal sex differences were examined in 5 major cell types (trophoblasts, stromal cells, hofbauer cells, antigen presenting cells, and endothelial cells). Ligands from the CCL family, with their receptors present on the maternal surface, were most representative in females. Maternal-fetal crosstalk shows sexual dimorphism during placentation early in gestation.