Endometrial hormone receptors and proliferation index in the periovulatory phase of stimulated embryo transfer cycles in comparison with natural cycles and relation to clinical pregnancy outcome

Objective: To investigate the endometrial steroid receptors and proliferation index in GnRH analogue/hMG-stimulated cycles in comparison with natural cycles and their relation to clinical pregnancy outcome. Design: Prospective observational study. Setting: Tertiary referral center. Patient(s): Twenty-seven stimulated patients with GnRH agonist and hMG. Twenty normo-ovulatory patients were the natural cycle controls. Intervention(s): Endometrial aspiration biopsies: in stimulated cycles on the day of oocyte retrieval within the ET cycle (Day OPU) (n = 20) or 2 days later (Day OPU + 2) (n = 7); in natural cycles on the natural day of ovulation (Day NO) (n = 10) or on the day of ovulation + 2 (Day NO + 2) (n = 10). Main Outcome Measure(s): Comparison of endometrial maturation, estrogen (ER) and P receptor (PR), and proliferation index by immunohistochemistry in natural and stimulated cycles, correlation with pregnancy outcome in stimulated cycles. Result(s): Stimulated cycles Day OPU showed significantly advanced endometrial maturation compared to natural cycles Day NO; stromal ER and glandular and stromal PR staining was lower in stimulated than in natural cycles, but higher on Day OPU than on Day NO + 2; proliferation index was lower in all stimulated cycles. Steroid receptors and proliferation index in stimulated cycles were unrelated to clinical pregnancy occurrence. Conclusion(s): Compared to natural cycles, ovarian stimulation induced an imbalance in endometrial ER and PR and led to a profound antimitotic effect in the peri-ovulatory phase. These parameters were, however, not predictive of clinical pregnancy in cycles with ET.