Bacterial vaginosis and its association with infertility, endometritis, and pelvic inflammatory disease Original paper

What was reviewed?

This review article comprehensively examines the associations between bacterial vaginosis (BV), endometritis, pelvic inflammatory disease (PID), and infertility, with a particular focus on the underlying microbiome-related mechanisms. The paper synthesizes current evidence on how disruptions in the vaginal and endometrial microbiota, characterized predominantly by a loss of beneficial lactobacilli and an overgrowth of anaerobic bacteria, contribute to the pathogenesis of these gynecological conditions. The review covers diagnostic criteria, treatment options, recurrence issues, and the role of the vaginal and endometrial microbial signatures in affecting reproductive outcomes, both naturally and in assisted reproduction settings. It also explores potential mechanistic pathways linking these infections to infertility, including inflammation, immune responses, microbial toxin production, and increased susceptibility to sexually transmitted infections (STIs).

Who was reviewed?

The review synthesizes data from a broad range of studies involving women of reproductive age, particularly those diagnosed with BV, endometritis, or PID, as well as women experiencing infertility (including those undergoing fertility treatments such as in vitro fertilization [IVF]). It considers diverse populations, including women with tubal and non-tubal infertility, women with unexplained or idiopathic infertility, and those with recurrent implantation failure or miscarriage. The article also references clinical trials and meta-analyses, drawing on evidence from both symptomatic and asymptomatic women across multiple ethnic groups and geographic regions.

Most important findings

The review highlights that optimal vaginal health is typically characterized by a microbiota dominated by lactobacilli, which produce lactic acid and antimicrobial compounds, conferring protection against pathogenic bacteria. BV is marked by a depletion of these protective lactobacilli and an overgrowth of anaerobes such as Gardnerella vaginalis, Atopobium vaginae, Megasphaera spp., and others. This microbial imbalance is strongly associated with an increased risk of endometritis and PID, both of which are significant causes of infertility. Notably, more than 85% of PID cases are linked to BV-associated bacteria and/or STIs, but fewer than half involve classic pathogens like Neisseria gonorrhoeae or Chlamydia trachomatis, underscoring the importance of the broader vaginal microbiome.

BV increases the risk of acquiring STIs, which further amplify the risk of upper genital tract infections and infertility. Mechanistically, BV-related bacteria can induce genital tract inflammation, alter immune responses, produce enzymes that degrade cervical mucus, and facilitate pathogen ascension to the endometrium and fallopian tubes. Women with BV and non-lactobacillus-dominated endometrial microbiota have lower implantation and pregnancy rates, particularly in IVF settings. Chronic endometritis (CE) is highly prevalent among women with unexplained infertility and recurrent implantation failure, and cure of CE with antibiotics improves reproductive outcomes. Despite these associations, causality between BV and infertility is not fully established due to heterogeneity in diagnostic criteria, patient populations, and study designs.

Key implications

The review underscores the clinical importance of recognizing and treating BV, endometritis, and PID—especially in women with infertility or at risk of reproductive complications. Early diagnosis and appropriate antibiotic treatment for symptomatic BV and CE can improve fertility outcomes, particularly in IVF patients. The findings also call for a more nuanced understanding of the vaginal and endometrial microbiome, advocating for future research to refine the definitions of “normal” versus “abnormal” microbial states and to clarify the mechanisms linking microbial dysbiosis to infertility. Given the high recurrence rates and diagnostic challenges, integrating microbiome-based diagnostics and interventions (including probiotics) into preconceptional and fertility care may offer new avenues for improving women’s reproductive health.