P-365 The composition of the endometrial microbiota, as determined by MicroBioMap®, significantly affects clinical outcomes in assisted reproduction treatments
Authors: Medina Ruiz L , Sarasa J , Ferrández-Rives M , Jurado I , Aizpurua J , Enciso M 
Published: June 2023

Abstract

Study question
How does the presence of specific pathogenic or health-promoting microbial species in the endometrium relate to female fertility in assisted reproduction treatments (ART)?

Summary answer
Detection of endometrial pathogens using MicroBioMap® is associated with poor ART outcomes, whereas sterile endometria show the highest pregnancy and live birth rates.

What is known already
Vaginal eubiosis is characterised by low microbial diversity and dominance of Lactobacillus, which displays bioregulatory functions and prevents the growth of pathogenic microorganisms. Vaginal dysbiosis is directly linked to infertility and poor pregnancy outcomes. However, the endometrial microbiota composition and its role in fertility are more controversial. Robust reports show that chronic endometritis (CE) is highly prevalent among infertile patients, whose outcomes improve after antibiotic treatment. However, the role of Lactobacillus in this compartment, whether it also displays bioregulatory functions, or if it is essential and beneficial for women undergoing ART, is still unclear.

Study design, size, duration
This is a case-control retrospective study analysing the endometrial microbiota in the window of implantation (WOI) and the ART outcomes of 456 women undergoing IVF cycles in egg donation regimes with/without PGT-A (177 and 163 respectively), or using their own eggs in cycles with/without PGT-A (91 and 25 respectively), between March 2016 and April 2021 in IVF-Life Alicante (Spain). ART results after single embryo transfer (sET) of patients with different endometrial microbiota profiles were compared.

Participants/materials, setting, methods
Presence of 18 microbial CE pathogens and 4 Lactobacillus species was determined by high-throughput qPCR (MicroBioMap®) in 456 endometrial samples obtained during the WOI (determined by ER Map® receptivity test) of a hormone replacement therapy cycle. Clinical outcomes (clinical pregnancy, CP; live birth, LB) of sETs performed during the WOI (guided by ER Map®) were compared in relation to the endometrial microbiota profile. In PGT-A cycles, embryo ploidy was determined by NGS (VeriSeq-MiSeq) before sET.

Main results and the role of chance
According to the microbial profile detected by MicroBioMap®, patients were categorised as i) Lactobacillus only (L, n = 199), ii) Pathogens only (P, n = 56), iii) Lactobacillus + pathogens (L+P, n = 59) or iv) Undetected (U, n = 142).
Absence of endometrial microorganisms was significantly associated to ART success. U-patients showed significantly higher CP (64.2% vs 50.8%, Fisheŕs exact p=0.046) and LB rates (52.9% vs 37.2%, p=0.03) after euploid sET than patients with microorganisms. These differences were more pronounced in patients receiving donor eggs (CP 70.2% vs 50.8%, p=0.026; LB 59.5% vs 40.2%, p=0.046).
Presence of Lactobacillus in isolation in the endometrium showed a detrimental effect compared to U-environments. A trend towards statistical significance was detected, with L-patients showing lower LB rates compared to U-patients after euploid sET (38.8% vs 52.9%; p = 0.084).
Detection of endometrial pathogens significantly reduced ART success rates. P-patients had significantly lower CP rates (64.2% vs 41.2%, p=0.038) after euploid sET than U-patients, and significantly lower CP (70.2% vs 36%, p=0.006) and LB rates (59.5% vs 21.7%, p=0.004) if receiving donor eggs. Interestingly, Lactobacillus dominance in pathogen-positive patients seemed to improve outcomes after euploid sET compared to pathogen-dominated patients (CP 56.7% vs 42.2%; LB 41.7% vs 31%).

Limitations, reasons for caution
This is a retrospective study. Randomised-control trials, non-selection studies and/or other investigations including antimicrobial treatments are needed to confirm these results and the extent of any clinical benefits. Endometrial biopsies were obtained transcervically. Although utmost care was taken, risk of contamination from the lower genital tract cannot be completely excluded.

Wider implications of the findings
Our results suggest that sterile endometria provide the best conditions for embryo implantation and pregnancy. Lactobacillus presence in endometrium might not be essential for pregnancy, and could even be detrimental if found in isolation. Presence of Lactobacillus as a bioregulator might only be beneficial if other pathogens co-colonise the tissue.

Trial registration number
Not applicable