ABSTRACT
The establishment of pregnancy requires an interaction between the embryo, uterus, and corpus luteum (CL). These interactions prevent luteal regression by extending the functional life span of the CL.1 Successful implantation requires a genetically normal embryo and a receptive uterine endometrium.2 Uterine receptivity has been defined as the limited period of time when the uterine luminal epithelium is favorable to blastocyst implantation.3 Estrogen and progesterone play a critical role in establishing the receptive phase. However, it is becoming increasingly evident from rodent studies that the embryo induces functional receptivity, which is required for successful nidation.4
