Embryonic Modulation of Endometrial Receptivity

Abstract: Implantation requires a receptive endometrium, a functionally normal embryo and communication between the developing embryo and maternal tissues (cross-talk). Two-step embryo transfer (two-step ET) and stimulation of endometrium embryo transfer (SEET) are procedures for ET based on concept of embryonic modulation of endometrial receptivity. In two-step ET, a cleaved embryo is transferred on day 2, and a blastocyst is transferred on day 5. The pregnancy and implantation rates with two-step ET were found to be higher than those with cleaved ET and double blastocyst transfer. We speculated that the cleaved embryos transferred on day 2 modulate endometrial receptivity and improve the implantation rate for blastocysts transferred on day 5. In SEET, embryo culture supernatant (ECS) is injected into the uterine cavity prior to blastocyst transfer to stimulate the endometrium and provide an optimum environment for implantation of forthcoming blastocysts. The pregnancy and implantation rates with SEET were found to be higher than those with blastocyst transfer. Higher implantation and pregnancy rates with SEET could be explained by embryonic factors produced in the culture medium that modulate endometrial receptivity. Lysophosphatidic acid was detected in ECS. Two-step ET and SEET are effective options for ET based on the concept of crosstalk between embryos and maternal tissues.