What is already known
Recent studies suggest how the vaginal and endometrial microbiota may have an impact on reproductive health and pregnancy outcomes.
What this research adds
The authors aim to explore existing literature on the relationship between the vaginal, endometrial, and gut microbiome and recurrent pregnancy loss, identifying potential areas for future research.
Conclusions
Taking microbial health into account in reproductive medicine is fundamental. Nevertheless, more research on the potential benefits of using the microbiome to improve fertility outcomes is still needed.
The vaginal and endometrial microbiota may have an impact on reproductive health and pregnancy outcomes.
A significant number of women is affected by recurrent pregnancy loss, meaning two or more consecutive pregnancy losses. Half of these cases remain unjustifiable, raising the urgency for a better understanding of the underlying mechanisms.
A systematic review recently published in the Journal of Reproductive Immunology by Kilian Vomstein and colleagues from the Copenhagen University Hospitals provides a comprehensive overview of the emerging role of the microbiome in recurrent pregnancy loss (RPL). Below are the main findings.
Microbiome Composition
Adverse pregnancy outcomes seem to be associated with an imbalanced microbial composition. In particular, compared to normal gestations, women with RPL showed:
- Higher presence of several taxa like Fannyhessea vaginale, Prevotella, or Streptococcus at the vaginal level, mixed results for Lactobacilli and other few taxa. Also, aerobic vaginitis resulted 5 times more prevalent in the RPL group.
- Dysbiosis in the endometrial microbiome. Indeed, a higher presence of Proteobacteria, Dialister, Anaerobacillus, Erysielothrix, Hydrogenophilus spp., and Ureplasma spp. was correlated with an increase in preterm delivery and pregnancy loss.
- A decrease in microbial diversity and in relative abundance for taxa like Prevotellaceae and Selenomonas in the gut microbiome. On the contrary, Megasphaera and Enterococcus showed enrichment in RPL women.
Links between microbiome and RPL
Pregnancy may be impacted by the microbiome via a number of pathways, including metabolite synthesis, immune response modulation, and localized inflammation.
If dysbiotic, the microbial population can lead to inflammation, which may contribute to RPL. A vaginal raise of Gardnerella and Ureaplasma, while a depletion of Lactobacillus, for example, was correlated with a pro-inflammatory state.
Clinical Implications
Alterations in the vaginal and endometrial microbiome in the RPL group suggest potential microbial markers. Therefore, novel diagnostic tools could rely on microbial profiling.
Moreover, potential interventions include probiotics instead of antibiotics to support the growth of beneficial bacteria. Not only. The vaginal microbiota transplantation is a preliminary option to restore a healthy microbial balance.
In summary, the microbiota represents a potential resource for comprehending recurrent pregnancy loss. Unfortunately, despite the growing number of evidences in this area, more interventional studies are still required to determine the causal links between RPL and changes in the microbiome.
