JBRA Assisted Reproduction 2025;29(Suppl.2 SBRA 2025):232
Poster Presentation
29^th Annual Congress of the SBRA. São Paulo/SP - Brazil, 2025
doi: 10.5935/1518-0557.20263849

P-220. The association between endometrial microbiome profiles and live birth rates in in vitro fertilization cycles: a narrative review

Isabella Kassamanian Afonso¹, Endjeli Vogler Reche¹, Milena de Souza Gomes Luiz¹, Maria Mônica Pereira¹

¹ Centro Universitário São Camilo - São Paulo – SP - Brasil

Objective: To evaluate the association between endometrial microbiome (EM) profiles and live birth rates in in vitro fertilization (IVF) cycles.
Methods: This was a narrative literature review of studies indexed in the Medline (PubMed) database over the past ten years, combining terms related to IVF, microbiome, and endometrium, resulting in 35 articles retrieved. Two independent reviewers performed screening using the Rayyan platform, with conflicts resolved by a third reviewer. Subsequently, the selected full-text articles were analyzed, including observational studies and randomized clinical trials that evaluated the EM using molecular methods or microbiological culture in infertile women. Exclusion criteria were studies without outcome data, reviews, editorials, and case reports. Extracted data included study type, sample size, mean age, and outcomes.
Results: Seven studies were included: two prospective observational studies, three retrospective observational studies, one retrospective/prospective cohort, and one secondary analysis of a randomized clinical trial. The mean sample size was 149 participants, with a mean age of 35.64 years. The presence of pathogenic bacteria such as Streptococcus, Staphylococcus, and Neisseria was associated with reduced Lactobacillus spp., an increased risk of implantation failure, and pregnancy loss. Studies showed that among bacteria present in the EM, Lactobacillus species were prevalent in women with successful pregnancy outcomes, whereas pathogenic species (Streptococcus, Staphylococcus, Neisseria) were predominant in unsuccessful cases. In a study of patients with repeated implantation failure, 88.7% presented pathogenic bacteria in the endometrium, and Lactobacillus dominance was significantly lower in these cases (DR=54.5%; p<0.01). Patients with pathogenic microbiota received antibiotic treatment before subsequent embryo transfer, which increased clinical and ongoing pregnancy rates compared to the pathogen-free group, although without statistical significance (p>0.05). Another study found that combining antibiotics with vaginal Lactobacillus supplementation for dysbiosis treatment resulted in higher pregnancy rates than antibiotics alone or no dysbiosis; dysbiosis treatment was the only factor associated with clinical pregnancy in multivariate analysis. In another study, groups with live births showed higher abundance of Lactobacillus crispatus, suggesting that an endometrium dominated by this species may enhance receptivity and implantation, increasing the likelihood of live birth. However, one study reported Lactobacillus dominance in only 8% of EM samples, with a clinical pregnancy rate of 30% and a live birth rate of 19%. Additionally, bacterial diversity was higher in women who conceived. Therefore, no significant association was found between this microbiome profile and pregnancy or live birth rates. Chronic endometritis (CE) was identified in 31.4% of patients with recurrent implantation failure, with an increase in multidrugresistant CE (MDR-CE) cases in recent years. Although both resistant and sensitive profiles were often dominated by Lactobacillus, persistent inflammation was more intense in resistant cases. Antibiotic treatment showed similar effectiveness in both groups, with comparable live birth rates. These findings reinforce that endometrial microbiota and inflammation are interconnected and may impact pregnancy outcomes.
Conclusion: The endometrial microbiome may directly influence assisted reproduction outcomes through both its composition and functional activity. Lactobacillus appeared to play a positive role in this environment. However, further research with higher methodological quality is needed to clarify the mechanisms involved, identify differences between outcomes related to natural conception and IVF, and improve treatments for microbiota-associated infertility.