O-198 Thin endometrium patients suffer from a higher risk of window of implantation displacement - A propensity score matching study

Abstract Study question What is the relationship between endometrial thickness and endometrial receptivity? Summary answer Thin endometrium patients exhibit a significantly higher percentage of window of implantation displacement. Patients with at least one previous implantation failure show similar results. What is known already Endometrial thickness measured by ultrasound represents an indirect parameter to determine the endometrial receptivity stage; however, this stage can be determined more accurately via an endometrial biopsy by performing a transcriptomics-based endometrial receptivity analysis that identifies the window of implantation as standard or displaced. A thin endometrium (<6 mm) is associated with poor reproductive outcomes, with some studies reporting a greater degree of window of implantation displacement in these cases; however, potential reasons remain unknown. Study design, size, duration 45,780 infertile patients were included in a retrospective study. Cohorts were classified according to endometrial thickness: <6 mm (n = 385), 6-12 mm (n = 41,764), or > 12 mm (n = 3,631). The propensity score strategy (1:2) was applied using the variables of age, BMI, and number of previous implantation failures. The results of the endometrial receptivity analysis were related to endometrial thickness. The same analysis was performed in a subgroup of patients with at least one previous implantation failure. Participants/materials, setting, methods By a longitudinal view of the endometrium using 2D ultrasound before progesterone initiation as part of a hormone replacement therapy cycle, endometrial thickness was measured from one endometrial layer to the other at the maximum site of thickness. Endometrial biopsies were performed after five days of progesterone administration. RNA was extracted and sequenced by next-generation sequencing using a computational predictor that obtained a diagnosis of standard or displaced window of implantation. Main results and the role of chance The endometrial receptivity analysis results revealed that thin endometrium patients (<6 mm) presented a significantly higher incidence of window of implantation displacement (174/385= 45.19%) than normal (6-12 mm; 256/770= 33.25%) and hypertrophic (> 12 mm; 250/770= 32.47%) endometrium patients (p < 0.001). Atrophic patients displayed a significantly higher frequency of post-receptive (16/385=4.16%) and 2 days pre-receptive (15/385=3.9%) results than normal (19/770=2.47% and 8/770=1.04%), and hypertrophic (11/770=1.43% and 8/770=1.04%) endometrium patients, respectively (p < 0.001). Results analyzed from the total sample size (before applying propensity score strategy) revealed the same trend, with a higher incidence of window of implantation displacement in atrophic (174/385=45.19%) compared to normal (13,834/41,764= 33.12%) and hypertrophic patients (1,155/3,631= 31.78%). A subanalysis from patients with at least one previous implantation failure revealed a similar displacement distribution in atrophic (89/198=44.95%), normal (134/397=33.75%), and hypertrophic (119/396=30.05%) endometrium patients (p < 0.001). Limitations, reasons for caution This study suffers from the inherent limitations of a retrospective study; furthermore, this descriptive study does not provide information regarding reproductive outcomes. Wider implications of the findings Our study highlights more significant window of implantation displacement in thin endometrium patients (<6 mm); however, normal thickness (6-12 mm; “receptive”) does not preclude an abnormal transcriptomic receptivity status, as shown in 33.12% of cases. This finding should be considered when applying an optimal methodology to assess endometrial receptivity. Trial registration number No