Research question:
Precise timed synchronization between endometrium and the embryo is essential for high implantation and pregnancy rate, it is worthy to mention that endometrial thickness is not the only factor, E2 and P levels are also regularly monitored for endometrial receptivity. So, we decided to go for this study, to investigate the impact of serum E2 and P levels on the same day of embryo transfer on pregnancy outcomes for FET cycles.