In attempts to correlate endometrial development and the establishment of an ongoing pregnancy,all endometria on the day of oocyte retrieval in stimulation regimens showed advancement of >2 days as compared to a natural cycle endometrium on the day of ovulation.Some other researches also had the results which supported the relationship between endometria and stimulated cycles.Endometrium within the cycle of embryo transfer have shown a deleterious effect of severe peri-ovulatory maturation advancement exceeding 3 days,as no clinical pregnancies were obtained in this condition.In a research to compare gene expression profiles and structural/functional features of the peri-implantation endometrium in natural and gonadotropin-stimulated cycles,findings show as follows:first,COS cycles depicted structural and functional changes when compared with natural cycles(i.e.the expected histological advancement and steroid receptor down-regulation) that were associated with significant,but small,changes in gene expression.Second,there were significant changes in gene expression when comparing cycles using a GnRH agonist vs.a GnRH antagonist(in the absence of other structural or functional changes).Some of these genes have been cited as relevant for implantation.So we can have our conclusion as that local injury to the endometrium doubles the incidence of successful pregnancies in patients undergoing in vitro fertilization.There are two possible reasons.First,decidualization provoked by injury,raised the idea of possible involvement of histamines that are released by the uterine tissue in response to this trauma.Another possible mechanism by which endometrial sampling may increase its receptivity could possibly involve events that accompany wound healing.Our results demonstrate that local injury to the endometrium to remove with endometrial polyps or thickened endometrium 1-2 weeks before embryo transfer significantly improves the success rate of pregnancy.After three failures,repeated hysteroscopy(local injury) and a try of b
