Clinical pregnancy rate in IVF cycles depends on embryo quality and endometrial receptivity . It is challenging to assess endometrial receptivity. Measuring endometrial thickness by ultrasonography is a simple , noninvasive and accurate method to do so. Many studies have implicated endometrial thickness and pattern as prognostic parameters for successful outcomes in IVF-ET.~Some studies have suggested a minimal thickness for a successful pregnancy to occur, while others have reported adverse effects of increased endometrial thickness above which pregnancy is unlikely to occur.~Now there is a novel hypothesis that not only the initial endometrial thickness can affect implantation rate and clinical pregnancy rate ,but also the decrease in endometrial thickness in the time interval between the ovulation triggering and the embryo transfer or what is called endometrial compaction increases the implantation and clinical pregnancy rate
To record the dynamic change of endometrial thickness (Day of embryo transfer Versus. Day of ovulation trigger administration in case of fresh cycles or end of estrogen phase in frozen cycles), and to investigate the impact of endometrial thickness change on pregnancy outcomes