Scientific Resources - Female Fertility and Vaginal Microbiome

The vaginal microbiome is essential for women’s health, especially in terms of reproductive health and fertility. This intricate microbial community, primarily composed of Lactobacillus species in most healthy women, plays a vital role in preventing infections and creating a favorable environment for conception and pregnancy. When this balance is disrupted, as seen in conditions like bacterial vaginosis or dysbiosis, it can affect fertility outcomes, including the effectiveness of assisted reproductive technologies (ARTs) such as IVF.

As the interest in the relationship between the vaginal microbiome and fertility increases, researchers are discovering new information about how microbial composition affects reproductive health and what strategies might help restore balance. This blog post offers a curated selection of scientific resources, summarizing key findings from academic studies on the vaginal microbiome, its effects on fertility, and potential methods for enhancement. Each summary includes a link to the original paper, enabling readers to explore the science further if they choose.

Below, you’ll find summaries of significant studies that illuminate this intriguing subject. Let’s examine how the vaginal microbiome impacts fertility and what insights we can gain to better support reproductive health.

1. Towards a Deeper Understanding of the Vaginal Microbiota

This paper highlights the critical role of the vaginal microbiota in maintaining vaginal health. While healthy vaginal microbiota are often dominated by Lactobacillus species, some women have microbiota with fewer Lactobacilli and more anaerobes, which have been linked to adverse health outcomes. The review delves into the biology of Lactobacillus-dominant versus non-dominant microbiota, exploring host factors that shape these communities. Current approaches like probiotics and vaginal microbiome transplants are discussed, alongside a call for advanced models of the cervicovaginal environment to shift research from associations to causative mechanisms.

Link to full paper: https://www.nature.com/articles/s41564-022-01083-2

2. The Female Vaginal Microbiome in Health and Bacterial Vaginosis

This paper reviews the dynamic nature of the vaginal microbiome, which evolves throughout a woman's life and menstrual cycle. A healthy microbiome is typically Lactobacillus-dominant, which protects the host through antimicrobial production. However, bacterial vaginosis (BV) arises when Lactobacilli decrease and anaerobes like Gardnerella vaginalis proliferate. BV is highly prevalent among women of reproductive age and is associated with serious health risks, including pelvic inflammatory disease, sexually transmitted infections, and preterm birth. The review summarises advancements in understanding BV’s mechanisms, diagnosis, and treatment strategies, with a focus on recent research developments.

Link to full paper: https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2021.631972/full

3. Finding a Balance in the Vaginal Microbiome: How Do We Treat and Prevent the Occurrence of Bacterial Vaginosis?

This review focuses on bacterial vaginosis (BV), a condition affecting one-third of women worldwide and often characterised by abnormal vaginal discharge and dysbiosis in the vaginal microbiota. Despite advancements in molecular tools to monitor microbial imbalances, treatment failure and recurrence rates remain high with standard antibiotics. The paper explores alternative strategies, such as probiotics and vaginal microbiota transplants, to restore vaginal health and reduce the colonisation of pathogenic microbes. It highlights the promise of these innovative approaches in improving treatment outcomes and achieving long-term vaginal microbial balance.

Link to full paper: https://pmc.ncbi.nlm.nih.gov/articles/PMC8232816/

4. Vaginal Microbiome and Its Relationship to Behavior, Sexual Health, and Sexually Transmitted Diseases

This review highlights the critical role of the vaginal microbiota in protecting against disease and maintaining reproductive health. Advances in molecular tools have enabled detailed studies of microbial composition and its links to behaviour, sexually transmitted diseases (STDs), and adverse birth outcomes. The vaginal microbiota clusters into dynamic community types, with Lactobacillus-dominated communities, particularly those with Lactobacillus crispatus, being most protective. Factors influencing microbiome composition include both modifiable behaviours and nonmodifiable traits like race and hygiene. The review examines these determinants and explores how microbiome research intersects with broader behavioural and public health contexts.

Link to full paper: https://pmc.ncbi.nlm.nih.gov/articles/PMC6743080/

5. The Role of Genital Tract Microbiome in Fertility: A Systematic Review

This systematic review examines the impact of the genital tract microbiome on fertility, including its role in assisted reproductive treatments (ARTs). The analysis of 26 studies highlights that a Lactobacillus-dominated microbiome, particularly Lactobacillus crispatus, is strongly associated with improved fertility outcomes. Conversely, the presence of pathogens such as Chlamydia trachomatis, Gardnerella vaginalis, and Ureaplasma species negatively affects fertility, even in asymptomatic cases of bacterial vaginosis (BV). The paper calls for standardised sampling methods and advanced research, particularly on the tubal microbiome, to better understand and optimise fertility potential and treatments.

Link to full paper: https://pmc.ncbi.nlm.nih.gov/articles/PMC8745627/

6. Identification of Vaginal Microbiome Associated with IVF Pregnancy

This study examines the differences in vaginal microbiome composition between women who conceived naturally and those who conceived through IVF, particularly regarding the increased risk of preterm birth (PTB) in IVF pregnancies. Using 16S rRNA sequencing, researchers found significant differences in beta diversity and genus composition between the two groups. Women in the IVF group exhibited higher abundances of genera such as Gardnerella, Neisseria, Prevotella, and Staphylococcus, as well as species-level differences like increased Lactobacillus iners and decreased Lactobacillus gasseri. These findings suggest that specific microbial signatures could predict IVF pregnancy outcomes and their association with PTB risk.

Link to full paper: https://www.nature.com/articles/s41598-022-10933-2

7. Characterisation of the Vaginal Microbiome in Women with Infertility and Its Potential Correlation with Hormone Stimulation during IVF

This study explores the vaginal microbiome composition of women undergoing IVF compared to healthy women. Women with infertility showed reduced microbiome diversity and richness compared to healthy controls, particularly during the follicular phase. Infertile women also exhibited distinct microbial shifts, such as an increased abundance of Atopobium, Aerococcus, and Bifidobacterium, alongside a decreased presence of Lactobacillus and Leuconostoc. Interestingly, hormone stimulation during IVF (e.g., GnRH agonist and r-hCG induction) did not significantly alter the vaginal microbiome of infertile women, suggesting stable microbiota patterns under these conditions.

Link to full paper: https://journals.asm.org/doi/10.1128/msystems.00450-20

8. Fertility Factors Affect the Vaginal Microbiome in Women of Reproductive Age

This study investigates how various fertility-related factors, such as age, hormone levels, tubal patency, and vaginal pH, influence the vaginal microbiome composition in reproductive-age women. Using 16S rRNA sequencing, the study found that higher vaginal pH, abnormal menstrual cycles, or tubal obstruction correlated with an increased abundance of Escherichia coli. Basal hormone levels (e.g., E2, LH, and FSH) were also significant determinants of microbial composition. Species like E. coli, Streptococcus agalactiae, and Prevotella intermedia were identified as potential biomarkers of reproductive tract health and endocrine conditions.

Link to full paper: https://pmc.ncbi.nlm.nih.gov/articles/PMC7078941/