Speaker- Courtney Povey

A study investigated microbial compositions in the vaginal and endometrial microbiomes. While the vaginal microbiome, dominated by lactobacillus species, is well-characterized, the endometrial microbiome, once thought sterile, has been identified with lower microbial diversity. The study explored whether these sites share similar microbial profiles, which is crucial for understanding their roles in reproductive health and their impact on outcomes in assisted reproductive technologies (ART). Different sampling methods—biopsies for the endometrium and swabs for the vagina—were employed due to accessibility and invasiveness. Vaginal sampling, less invasive and ethically uncomplicated, offers advantages for broader studies. Despite challenges like contamination risks and technical complexity in endometrial sampling, understanding microbial similarities between these sites could potentially replace more invasive biopsies with more accessible and cost-effective tests in clinical practice. The study underscores the importance of exploring less invasive alternatives to enhance the understanding and treatment of reproductive health issues related to microbial balance.

The study aimed to assess the correspondence between vaginal and endometrial microbiomes in 59 IVF (In vitro Fertilization) patients. During the mid-cycle of a cycle preceding frozen embryo transfer, paired endometrial biopsies and vaginal swabs were collected. Microbial DNA was extracted and analysed using qPCR (Quantitative Polymerase Chain Reaction), detecting 19 bacterial species, including four lactobacillus species known for their commensal role and 15 species commonly associated with dysbiosis. It explored whether vaginal sampling could reliably reflect the microbial composition of the endometrial microenvironment, which is crucial for optimizing reproductive health interventions like IVF. 

The study suggests processing differences were evident between vaginal swabs and endometrial biopsies due to the latter's low microbial load, requiring additional steps like enzymatic lysis and preamplification. Despite these challenges, both sites showed similar microbial compositions dominated by lactobacilli, with comparable abundances of dysbiotic species like Gardnerella vaginalis. The findings challenge previous notions of greater endometrial microbial diversity compared to the vagina, suggesting methodological influences. Direct comparisons indicated strong similarities in microbial profiles between the two sites, with minor discrepancies observed in a few cases, possibly influenced by factors like prior antibiotic use or reproductive treatments. 

Some patients exhibited less favourable vaginal compositions compared to the endometrium. Possible reasons include prior oral probiotics or antibiotics use and treatments for conditions like chronic endometritis, which were identified through patient questionnaires. The literature suggests that oral antibiotics and probiotics, often containing Lactobacillus crispatus, may not efficiently modify the vaginal microbiome. The study's cross-sectional design limits conclusions on longitudinal changes in microbial composition. Addressing confounding factors is crucial for accurate study outcomes. 

The remarkable similarity between the vaginal and endometrial microbiomes suggests that minimally invasive vaginal sampling could potentially replace invasive biopsies, facilitating improved patient recruitment in the study and streamlined application of validated clinical tests. 

Endometrial sample contamination risks were addressed through standard clinic protocols, with potential mitigation using specialized catheter techniques. The study suggests that vaginal samples may sufficiently reflect endometrial microbiota, revealing significant similarities between the two sites. Further investigation is needed to validate the relationship conclusively. Using qPCR, it effectively detected bacterial DNA in low biomass endometrial samples, demonstrating higher sensitivity than culture-based methods. However, additional studies are warranted to assess these microbial findings' viability and clinical relevance. Future studies should explore how microbiota variations impact endometrial development before embryo transfer, potentially offering insights into optimizing reproductive health outcomes. 

European Society of Human Reproduction and Embryology, July 7-10, Amsterdam, The Netherlands