Histological evaluation of human endometrium at different phases of hCG-primed menstrual cycle

Implantation is a complex process of interactions between the embryo and the endometrium, a layer of mucous membrane on the inner surface of the uterus. The embryo qualities making it fit for embedding, endometrium receptivity, as well as the exchange of multiple molecules between embryo and endometrium, determine whether and when is the best time for pregnancy to occur. In the context of a larger study we are conducting on the dynamics of microRNA expression in endometrium, an objective assessment of the endometrial phases is necessary. Here we present the outcome of endometrial phase assessment by applying a set of criteria in combination with human chorionic gonadotropin (hCG) administration which is considered to cause ovulation within 36-48 hours and allow for more accurate secretory phase dating. Endometrial biopsies were taken from 7 volunteers, outpatient and without anesthesia. Ultrasound measurements of leading follicle and endometrial thickness, together with eestradiol and luteinizing hormone levels were set as criteria for hCG application. It was applied on a strictly individual day for each patient as an inducer of ovulation. Biopsies were planned individually for each woman and conducted at 4 time points – hGC (before hormone application), hGC+2, hGC+7 and hGC+9 (numbers are days after hCG application). Part of each biopsy material was subjected to a classic histological examination by staining with hematoxylin and eosin, and the morphological evaluation was done according to the Noyes criteria. Quality and informative histological preparations for all 4 time points were produced only for 5 of the 7 volunteers. We observed that the histological descriptions at hGC+7 and hGC+9 time points showed no absolute compliance with the Noyes criteria for the corresponding secretory phases for some of the individuals. Thus, we created a new group of endometrial samples according to the Noyes criteria that correspond to the mid-secretory phase which includes 4 samples from LH+9 and 1 sample from LH+7. We consider it as the most representative pool of the most suitable period in receptivity terms to be used to analyze the dynamics of microRNA expression in the next stage of the ongoing project