Vaginal microbiome: a cause of miscarriage ?

By Ana Espino | Published on February 18, 2026 | 3 min read

 Recurrent pregnancy loss (RPL) affects approximately 1–2% of women of reproductive age and represents a major issue in gynecology and obstetrics. It is defined as the occurrence of at least two consecutive pregnancy losses before 20 weeks of gestation. Although certain causes have been identified (chromosomal abnormalities, coagulation disorders, immunological factors), in nearly 50% of cases no clear triggering factor is found, which considerably complicates management.

Currently, therapeutic approaches remain fragmented and often empirical, combining hormonal treatments, antiplatelet agents, or immunomodulators without robust evidence of effectiveness for all patients. This uncertainty reflects the limitations of the current biomedical model, which often overlooks environmental and microbiological factors.

Among emerging avenues of research, the vaginal microbiota has attracted growing interest. Under normal conditions, an ecosystem dominated by Lactobacillus spp. provides protection against infection and maintains an acidic pH favorable to implantation. In contrast, dysbiosis—marked by the proliferation of anaerobic bacteria such as Gardnerella, Prevotella, or Atopobium—may promote inflammation, disrupt the maternal–fetal interface, and increase the risk of fetal loss.

In this context, the present study was initiated to analyze the role of the vaginal microbiome in recurrent pregnancy loss. The associated inflammatory, metabolic, and immune mechanisms were investigated. The objective was to evaluate therapeutic prospects, particularly through targeted modulation of this ecosystem.

What if miscarriage originated in the microbiota ?

This study is based on the analysis of vaginal microbiota composition, its derived metabolites, associated immune profiles, and their link with recurrent pregnancy loss. The selected studies include cervicovaginal sampling analyses, 16S rRNA sequencing, measurement of pro-inflammatory cytokines, and clinical cases of vaginal microbiota transplantation.

transplantation.   The results reveal that patients with RPL show a marked reduction in Lactobacillus species, with a predominance of potentially pathogenic bacteria such as Gardnerella vaginalis, Anaerobacillus, or Streptococcus. This imbalance is accompanied by an altered metabolic profile, with decreased protective lactate and increased pro-inflammatory biogenic amines, an exacerbated local inflammatory response (elevated IL-6, IL-8, TNF-α), and the presence of a bacterial biofilm resistant to standard antibiotic treatments. These changes lead to detrimental uterine immune activation, compromising maternal tolerance to the embryo and promoting implantation failure. Some studies highlight the potential of vaginal microbiota transplantation to restore a healthy ecosystem in refractory patients, opening the way to an innovative and personalized therapeutic strategy.

Rethinking miscarriage in the era of the microbiome