Endometrial changes in estrogen and progesterone receptor expression during implantation in an oocyte donation program

Implantation is the final and most important stage of embryogenesis and is of paramount importance in achieving a successful pregnancy. Progesterone and estrogen are steroid hormones responsible for the regulation of the implantation window and the current study hypothesised that their receptors may be implicated in women undergoing oocyte donation. A total of 15 women aged 25-32 years old (mean ± SD, 28.9±2.89) undergoing oocyte donation were recruited into the present study. Participants underwent ovarian stimulation with gonadotrophin-releasing hormone antagonist and recombinant follicle-stimulating hormone. Endometrial aspiration biopsy was performed on the day of oocyte retrieval and after 5 days (on days 0 and 5, respectively). Endometrial histology and evaluation of estrogen receptor (ER)α and progesterone receptor (PR)-B were performed on days 0 and 5. The ER nodal staining percentage on day 0 was age-associated, with patients aged <30 years demonstrating 100% staining and those aged >30 years exhibiting 90% staining. Pathological staining revealed statistically significant differences between days 0 and 5 following all staining procedures. Wilcoxon signed-rank test resulted in the following P-values, for ER (nodes % and stromal %) day 0/5, P=0.0001; for PR (nodes % and stromal %) day 0/5, P=0.0001 and P=0.035, respectively; for ER (grade nodes and stromal %) day 0/5, P=0.0001; and PR (grade nodes and stromal %) day 0/5 P=0.0001 and P=0.016, respectively. Synchronization between blastocyst development and the acquisition of endometrial receptivity is a prerequisite for the success of <i>in vitro</i> fertilisation (IVF). Aside from the recent discovery of molecules that are considered crucial for successful embryo implantation, assessing the functional characteristics of the endometrium may offer unique insights into this process, thus improving IVF results.