Late follicular phase endometrium histology and steroid receptor expression in stimulated cycles for in vitro fertilization/embryotransfer treatment (IVF/ET) with a gonadotropin releasing hormone antagonist/recombinant follicle stimulating hormone (GnRH antagonist/recFSH) protocol

Abstract

To study the effect of multifollicular ovarian stimulation for IVF/ET on the histology and the steroid receptors expression of estrogen (ER), progesterone (PR) and androgen (AR) in preovulatory endometrium. Prospective cross-over study. Ten infertile women with normal ovulatory function participating in IVF/ET program were enrolled in this study. Endometrial biopsies were taken in a natural cycle on the day of the onset of the surge of the luteinizing hormone (LH), and in a subsequent stimulation cycle on the day of human chorionic gonadotropin (HCG) injection for final oocyte maturation (both of these dates are designated as day LH0). Immunohistochemistry was performed using commercially available antibodies for evaluating ER, PR and AR endometrial expression. Metric variables were tested with the t-test for independent samples and t-paired test for non-independent variables while Fisher’s exact test was used to analyse nominal variables. All tests were two-tailed with a confidence level of 95% (p<0.05). As it was expected, in the stimulation cycles estradiol (1826 vs. 254 ng/L) and progesterone (1.0 vs. 0.7 μg/L) levels were statistically significant higher compared to natural cycles. Histological examination of biopsies both in natural and stimulated cycles showed no early secretory phenomena. However, in stimulated cycles PR expression was up-regulated in both glands (1.61 vs. 1.29, p<0.05) and stroma (1.95 vs. 1.53, p<0.05) whereas ER were down-regulated in both compartments of the endometrium (1.37 vs. 1.20 in glands, and 1.20 vs. 1.01 in stroma, P>0.05 respectively). AR immunostaining was almost absent in glands in both natural and stimulated cycles and there was no difference in the expression in stroma cells during stimulation. An ongoing pregnancy rate of 42.8% was observed (in three women no embryo was transferred either because of poor embryo quality or ovarian hyperstimulation syndrome). In endometrial receptivity investigations, cross-over studies are valuable as thus the interpatient variability is eliminated. Moreover by taking the day of LH surge as a reference point for your biopsy timing, dating accuracy can be improved. Although in our study we found no early secretory changes in stimulated endometria just prior the HCG injection, the ER and PR phenotype of these endometria, however, resembles the phenotype observed the first days of the luteal phase. This phenomenon indicates accentuated maturation of the endometrium in IVF stimulated cycles even since the preovulatory phase. The possible pathogenetic mechanism for this abnormality is the supraphysiological concentrations of estrogens and the subtle progesterone rise, before the ovulation triggering in stimulated cycles. Taking into account the evidence that extreme advanced endometrium maturation on the day of the oocyte retrieval has been associated with adverse pregnancy outcome, seems that endometrium records interventions during the follicular phase as well, which might have implications during the implantation window later in the luteal phase. In order to understand the critical period for human implantation especially during the stimulation cycles for infertility treatment, attention should be paid equally in both luteal and follicular phase parameters.