In monitoring ovulation, we assess the quality of the eggs through the pre-ovulatory serum hormone levels in part, and in IVF, we monitor the hormones, remove the follicles, form embryos by in vitro fertilization, and grade the embryos. Strangely enough, good eggs or good quality embryos do not always guarantee a successful pregnancy, and some people even experience repeated implantation failures, possible infertility, biochemical pregnancy or embryonic abortion, seed After eliminating the causes of the seeds, we need to consider the land factor, which is the endometrium. Under normal circumstances, the endometrium thickens and sheds periodically under the action of estrogen and progesterone, forming our menstrual cycle. The ability of the endometrium to allow embryo implantation and further growth and development is called “endometrial tolerance”, i.e. Figure 1, while in some people this window is delayed (Figure 2), advanced (Figure 3) or even shortened (Figure 4). So what exactly affects the receptivity of the endometrium to embryos? As shown in the figure below, a successful pregnancy cannot be achieved without a good embryo and a receptive endometrium, but current technology cannot directly detect the magical connection between the embryo and the endometrium that eventually allows the embryo to take root and germinate, but we can surgically address some morphological abnormalities, improve inflammation, immune status or metabolism with drugs that have been clearly Methods that can improve the embryo implantation rate. During ovulation promotion, the high estrogen status may also alter the endometrial tolerance, in which case it is recommended to abandon fresh cycle transfer and suggest whole embryo freezing to prevent the occurrence of hyperstimulation and also to avoid endometrial implantation window alteration that may affect embryo implantation. So, one should pay attention to endometrial factors of infertility and to embryonic development of the soil!