P-549 Endometrial eubiosis vs dysbiosis: what role does the abundance of Lactobacillus play in endometrial receptivity?
Authors: Pérez Sánchez M , Díaz López C , Martínez-Lara A , Cotán D , Diez-Tercero L , Sandalinas Alabert M , Horcajadas Almansa J A 
Published: June 2023

Abstract

Study question
Is there an influence of Lactobacillus relative abundance on the expression profile of a set of genes related to endometrial receptivity?

Summary answer
The abundance of Lactobacillus genus in endometrium does not affect key genes related to endometrial receptivity determination.

What is known already
Typically, endometrial eubiosis has been determined by a Lactobacillus genus dominant presence (at least 90%), whereas a lower presence of this genus has been considered as endometrial dysbiosis. However, in recent years this belief has been called into question due to the theory that an abundance greater than 50% could already be considered as "Lactobacillus dominance". Nevertheless, there are few studies that analyze the influence of the relative abundance of this genus on endometrial receptivity.

Study design, size, duration
A total of 61 patients (average age= 39.04 years) were included in the study. Patients went through an endometrial biopsy for microbiome testing. Endometrial samples were classified according to their abundance of Lactobacillus genus: 43 samples with &lt;90% (average age= 39.4 years) and 18 samples with = &gt;90% (average age= 38.1 years), and a gene expression analysis of a 48 genes-panel related to endometrial receptivity was performed.

Participants/materials, setting, methods
RT-qPCR was performed for detection of certain microorganisms and pathogens in endometrial biopsies. Samples were selected based on the absence of pathogens and the presence of a regular profile of the rest of microorganisms, and classified according to their abundance of Lactobacillus. Gene expression of 48 genes related to endometrial receptivity was analyzed by microfluidic RT-qPCR. Data was analyzed by Delta-Delta Ct method, and Fold change was determined using Wilcoxon test.

Main results and the role of chance
There are no significant differences (p &gt; 0.05) in terms of gene expression profile of a 48 genes set related to endometrial receptivity by the current threshold (Lactobacillus = &gt;90% vs Lactobacillus &lt;90%). According to this result, the abundance of Lactobacillus would not affect the window of implantation. In addition, of total samples with receptivity evaluation (N = 49), 76.9% of the Lactobacillus &gt;90% group are receptive, whereas in the case of the Lactobacillus &lt;90% group, the proportion of receptive endometria is 63.8%.

Limitations, reasons for caution
Results could be affected by sample size and by typification, since some Lactobacillus species which are not considered beneficial may be responsible for the genus dominance in samples. In addition, further research on the expression analysis of other genes and the influence of different microorganisms are required.

Wider implications of the findings
Abundance of Lactobacillus in endometrial samples does not seem to affect 48 genes related to receptivity. Endometrium functionality does not have to be related to implantation window, at least based on the abundance of Lactobacillus with a 90% cutoff. It would be necessary to evaluate if pathogens could alter it.

Trial registration number
Not applicable