Periodic elevation of regulatory T cells on the day of embryo transfer is associated with better in vitro fertilization outcome

Treg cells have been shown to be important in maintaining maternofetal tolerance, but the expression of Tregs in assisted reproductive technology (ART) in women on the day of embryo transfer (D0), 5 days (D5) and 14 days after ET (D14); the related factors influencing the expression levels of Tregs; the proliferation ability and the relevant cytokine epression by Tregs on D14 have not been investigated. In this study, 124 women undergoing in vitro fertilization-intracytoplasmic sperm injection (IVF/ICSI) were enrolled. Early morning fasting blood samples were obtained for the measurement of Tregs and other relevant indicators on the D0, D5and D14 days after ET. we showed that the Tregs were increased on D0 and D14 in pregnant women, while there was no obvious fluctuation in non-pregnant women. IL-10 and TGF-β levels and the expansion of Tregs were significantly higher in successfully pregnant women than in non-pregnant women on D14. The levels of E2, P did not significantly differ between the groups. We suggest that periodic elevation of Tregs on the day of ET was associated with higher embryo implantation rate after ART.