CD163 + M2-like monocytes increase in pregnant women with first-attempted frozen embryo transfer

Macrophages play a vital role in endometrial receptivity and embryo implantation. However, it remains unclear if macrophages in peripheral blood is associated with pregnancy outcomes of frozen embryo transfer during implantation window. 50 patients preparing for the first time of frozen embryo transfer (FET) and 17 patients with recurrent implantation failure (RIF) from December 2022 to March 2023 were included in our present study. The percentages of peripheral macrophages and other immune cells (B-cell, T-cell, NK cell) were evaluated by flow cytometry. The concentrations of cytokines were verified with an IMMULITE 1000 Immunoassay System. FET patients were categorized into pregnant and nonpregnant groups according to clinical outcomes, respectively. The proportion of peripheral CD68⁺CD163⁺ M2 macrophages was increased in pregnant women than in nonpregnant women among the first time of FET patients. CD4⁺ T helper cells were positively correlated with M2-like macrophages in these women. The pregnancy rate of women with higher peripheral CD163 + M2-like monocytes increased compared with women with lower peripheral CD163 + M2-like monocytes in an independent cohort according to the cutoff value of CD163 + M2-like monocytes in ROC curve. Our findings revealed that peripheral CD163⁺ M2 macrophages in implantation window were associated with pregnancy outcomes. This indicated that the importance of peripheral M2 macrophages at the implantation site for pregnancy success.