OPINION - Endometrial receptivity

Embryo implantation depends on the quality of the ovum and endometrial receptivity. Endometrial receptivity is a temporally unique sequence of factors that make the endometrium receptive to embryonic implantation. Implantation window is a period during which the endometrium is optimally receptive to implanting blastocyst (D6-10 postovulation). No conclusive evidence of age related histological changes in the endometrium. The biochemical markers of endometrial receptivity include endometrial adhesion molecules (e.g. integrins), endometrial anti-adhesion molecules (e.g. mucin 1), endometrial cytokines, endometrial growth factors, endometrial immune markers and other endometrial markers. Integrins are the best markers of endometrial receptivity. Most interest has been focused on the av β 3 integrin since it appears in endometrial glands and luminal surface on D20-21. Endometrial function test may be the most efficient way to directly assess endometrial receptivity prior to undergoing expensive ART procedures as it can identify unreceptive endometrium. Pinopodes, are morphological markers of endometrial receptivity, which persist for 24 to 48 hours between days 19 and 21 of the cycle. Non invasive assessment of endometrial receptivity includes, high resolution transvaginal ultrasonography (US), three-dimensional US, Doppler US, three-dimensional power Doppler US, magnetic resonance imaging and endometrial tissue blood flow. Four strategies for improving endometrial receptivity: to develop ovarian stimulation protocols that cause a minimum reduction in endometrial receptivity or may even increase it; to avoid the endometrium during stimulated cycles, to improve uterine vascularization and to treat the pathology.