JBRA Assisted Reproduction 2025;29(Suppl.2 SBRA 2025):93
Poster Presentation
29^th Annual Congress of the SBRA. São Paulo/SP - Brazil, 2025
doi: 10.5935/1518-0557.20263680

P-81. Endometrial Dysbiosis as a Predictor of Poor Reproductive Outcomes in Assisted Reproduction

Elisa Weirich Braido¹, Isadora de Carvalho Schamm¹, Sophia Abur Said¹, Júlia Prauchner de Castilhos¹, Isadora Hausen², Isabella Lanzarini Erdklee¹, Marta Ribeiro Hentschke¹

¹ Pontifícia Universidade Católica de Porto Alegre - Porto Alegre – RS - Brasil
² Universidade do Vale do Rio Dos Sinos - São Leopoldo - RS - Brasil

Objective: To evaluate the impact of endometrial microbiome dysbiosis on reproductive outcomes in women undergoing in vitro fertilization (IVF) through a literature review.
Methods: A literature review was conducted in PubMed and ScienceDirect using the DeCS/MeSH terms "Endometrial Microbiota", "Endometrial Microbiome", "Uterine Microbiome", "Endometrium Dysbiosis", "Endometrial Dysbiosis', "Embryo Implantation", "Implantation Rate", "Embryo Transfer", "ART", "IVF", "Reproductive Outcome", "Female" and "Women". Seven articles were included.
Results: An eubiotic endometrial microbiome contains 90% or more of Lactobacillus spp. concentration with minor populations of bacteria such as Streptococcus and Staphylococcus, supporting an anti-inflammatory and implantation-friendly uterine environment. Dysbiosis, defined by a concentration below than 90% of Lactobacillus spp. and predominance of species like Streptococcus and Gardnerella, is associated with activation of endometrial inflammatory pathways. Endometrium affected by dysbiosis exhibits increased levels of pro-inflammatory mediators (IL-6, IL-1β, HIF-1α, and COX-2) and decreased levels of anti-inflammatory factors (IL-10 and IGF-1), reflecting a reduced presence of Lactobacillus. Notably, the percentage of Lactobacillus shows a negative correlation with IL-6 and IL-1β, and a positive correlation with IL-10 and IGF-1. According to recent studies, the hormone IGF-1 appears to play a crucial role in follicular and embryonic development, emerging as a potential marker for embryo quality and implantation potential. Although a certain degree of inflammatory response and immune cell recruitment is necessary during the implantation window to establish maternal immune tolerance, persistent inflammation and prolonged imbalance favor the emergence of a dysbiotic environment. Dysbiosis seems to be associated with poorer clinical outcomes, such as lower implantation rates, ongoing pregnancies, and lower live births. Among eubiotic women, the abundance of Lactobacillus was inversely associated with the number of IVF cycles performed. Thus, an imbalanced endometrial microbiota may lead to the establishment of a persistently inflamed microenvironment, which could reduce the likelihood of embryo implantation.
Conclusion: The endometrial microbiota is recognized as an influential factor in reproductive outcomes. The microorganisms present in the endometrium modulate physiological and immunological responses, thereby affecting embryo implantation, placental formation, and gestational development. The absence of Lactobacillus dominance promotes an inflammatory uterine environment that is unfavorable to embryo implantation, negatively impacting IVF clinical outcomes. An increased presence of pro-inflammatory cytokines and a reduction in repair and growth mediators, such as IGF-1, indicate a relevant immune imbalance, whose modulation may represent a promising therapeutic strategy. The effects on endometrial receptivity justify the inclusion of microbiological assessment in the diagnostic routine of women with implantation failure. Therefore, identifying endometrial dysbiosis as a potential cause of infertility reinforces the importance of evaluating uterine microbiota in infertile women. It is worth noting that research on this topic remains scarce, and further studies are needed to establish diagnostic and management protocols tailored to the uterine microbial profile.