Surreal illustration of a flower blooming from a landscape of vaginal microbiota

Does Your Gut Matter for IVF Success? The Truth About Vaginal Microbiota and Fertility

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Theo Raines in Health & Wellness October 2026 • 4 min read.

"Unpacking the latest research on how vaginal microbiota profiles impact live birth rates in IVF cycles with donor eggs."


For couples navigating the complex world of infertility, in-vitro fertilization (IVF) offers a beacon of hope. Yet, despite advancements in reproductive technology, success isn't always guaranteed. Researchers are continually exploring factors that can influence IVF outcomes, from embryo quality to endometrial receptivity. Recently, the spotlight has turned to the vaginal microbiota – the community of microorganisms residing in the female reproductive tract – and its potential role in fertility.

A healthy vaginal microbiota is typically dominated by Lactobacillus species, which help maintain an acidic environment that protects against harmful pathogens. However, imbalances in this delicate ecosystem, a condition known as bacterial vaginosis (BV), have been linked to various reproductive health issues. But does BV, or other variations in vaginal microbiota, directly impact the success of IVF treatments?

A new study published in 'Reproductive BioMedicine Online' has investigated the relationship between vaginal microbiota profiles at the time of embryo transfer and live birth rates in women undergoing IVF with donated oocytes. This approach isolates the impact of the vaginal environment, removing potential confounding factors related to egg quality and ovarian stimulation. Let's dive into the findings and what they mean for your fertility journey.

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Vaginal Microbiota and IVF Outcomes

Research has examined whether vaginal microbiota composition is associated with IVF outcomes, including clinical pregnancy and implantation success. A November 1, 2025 study set out to evaluate that relationship and considered microbiota a potential modifiable and predictive biomarker in infertility treatment. A systematic review also assessed genital-tract microbiota in women undergoing assisted reproductive treatment and compared IVF outcomes across microbial compositions. A February 11, 2025 report noted that assessing vaginal microbiota before embryo transfer may help optimize transfer timing, while a March 19, 2024 study analyzed microbiota composition in relation to IVF outcomes.

The Vaginal Microbiota and IVF Outcomes: What the Study Revealed

Surreal illustration of a flower blooming from a landscape of vaginal microbiota

The study, conducted with 150 Caucasian women receiving donated oocytes, prospectively examined the vaginal microbiota composition at the time of embryo transfer. Researchers analyzed samples for the presence of key Lactobacillus species (L. crispatus, L. gasseri, L. jensenii, and L. iners) and bacteria associated with BV (Gardnerella vaginalis, Atopobium vaginae, Mycoplasma hominis, and Prevotella spp.). The goal was to determine if specific microbiota profiles correlated with live birth rates.

Here's a breakdown of the key findings:

  • Dominant Species: A majority of samples were dominated by a single species, with Lactobacillus spp. being the most prevalent.
  • No Direct Link to Live Birth: The overall distribution of microbiota profiles (Lactobacillus-dominated vs. BV-associated) was not significantly different between women who achieved live birth and those who did not.
  • L. crispatus Predominance: Interestingly, a significantly higher proportion of women achieving live birth had vaginal microbiota dominated by L. crispatus. This correlation also extended to biochemical and clinical pregnancy.
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Mixed Findings in Recent Reviews

A PRISMA systematic review and meta-analysis defined vaginal dysbiosis in one included study as a non-Lactobacillus-dominated microbiota, with Lactobacillus below 90%. Another systematic review reported that a study found no effect of vaginal microbiota on live-birth rates after IVF. In contrast, a 2026 systematic review reported that abnormal vaginal microbiota—defined by elevated Gardnerella vaginalis and/or Atopobium vaginae—was associated with lower clinical pregnancy rates. A separate review published April 10, 2026 describes the vaginal microbiome as a possible predictive biomarker and regulatory target for assisted-reproduction outcomes.

Limits of Microbiome Comparisons

The supplied comparative sources do not provide a direct comparison of vaginal microbiota and IVF outcomes. One source describes an animal embryo-transfer study comparing live-birth rates between B6CF1 and Kunming (KM) mice, using 362 embryos collected from 24 B6CF1 and 14 KM mice. Another reports that 30 of 41 embryos collected from six rabbit donors were transferred to seven recipients. A November 20, 2025 article by Dr. Senai Aksoy cautions that association is not causation and says routine vaginal or endometrial microbiome profiling is not recommended.

These findings suggest that while the overall presence of BV-like microbiota may not directly prevent live birth in IVF cycles with donor eggs, the dominance of specific Lactobacillus species, particularly L. crispatus, could play a positive role.

Implications and Future Directions: What This Means for You

This study offers valuable insights into the complex relationship between vaginal microbiota and IVF success. While it's reassuring to know that a BV-like environment may not automatically derail your chances, optimizing your vaginal health could potentially improve your odds, specially enrichment with L. crispatus.

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Gut and Vaginal Microbiome Research

A study described in Fertility and Sterility investigated the composition and functional profile of the gut and vaginal microbiomes in IVF patients. It examined their association with cycle outcomes in fresh embryo-transfer cycles. The supplied source description states the research question but provides no findings or outcome figures, so it does not establish whether either microbiome predicts IVF success.

The Vaginal Microbiome in Context

A review published December 24, 2024 describes a healthy vaginal microbiome as dominated by Lactobacillus species, a community also known as Döderlein flora. It reports Lactobacillus concentrations of 10⁷–10⁸ colony-forming units per gram of vaginal fluid in the lower genital tract. These figures and descriptions provide broader context about vaginal microbiota; the supplied passage does not specify how they relate to IVF outcomes.

Here are some key takeaways and steps to consider:

<ul><li><b>Focus on a Balanced Microbiome:</b> While more research is needed, maintaining a healthy vaginal environment with a dominance of beneficial bacteria like L. crispatus appears to be beneficial.</li><li><b>Consult Your Doctor:</b> Talk to your doctor about your vaginal health and whether testing or interventions are appropriate for your specific situation.</li><li><b>Future Research:</b> Further studies are needed to confirm these findings and explore the mechanisms by which L. crispatus may influence IVF outcomes. Researchers also need to investigate how different interventions, such as probiotics, could be used to optimize vaginal microbiota profiles and improve fertility.</li></ul>

What the live-birth comparison shows

  • 1.03 (95% CI 0.79–1.33; I² = 28%) relative risk per embryo transferAcross IVF patients, the relative risk of live birth per embryo transfer for vaginal dysbiosis compared with normal vaginal microbiota was 1.03 (95% CI 0.79–1.33; I² = 28%).[1]

What these microbiota comparisons can show

The live-birth estimate is close to no relative difference, while its confidence interval includes values on either side of no difference. That makes it compatible with a range of possible effects rather than proof that dysbiosis has no relationship to live birth.[1]

What remains unresolved about microbiota and IVF

  • Can a proposed endometrial inflammatory pathway explain some reported links between microbial communities and pregnancy outcomes, or does it remain a possible mechanism?[2] [3]
  • How much can findings from combined partner microbiome profiles tell us about the contribution of the vaginal profile alone?[4]

Sources

  1. The Association between Vaginal Dysbiosis and Reproductive Outcomes in Sub-Fertile Women Undergoing IVF-Treatment: A Systematic PRISMA Review and Meta-Analysis (pmc.ncbi.nlm.nih.gov)
  2. Longitudinal analysis of vaginal microbiota during IVF fresh embryo transfer and in early pregnancy (pmc.ncbi.nlm.nih.gov)
  3. Effect of L. crispatus M247 Administration on Pregnancy Outcomes in Women Undergoing IVF: A Controlled, Retrospective, Observational, and Open-Label Study (pmc.ncbi.nlm.nih.gov)
  4. Lactobacillus crispatus‐dominated vaginal microbiome and Acinetobacter‐dominated seminal microbiome support beneficial ART outcome (obgyn.onlinelibrary.wiley.com)

About this Article -

Written with AI assistance from published research, and reviewed by the Mystum team. See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.rbmo.2018.12.019, Alternate LINK

Title: Vaginal Microbiota Profile At The Time Of Embryo Transfer Does Not Affect Live Birth Rate In Ivf Cycles With Donated Oocytes

Subject: Developmental Biology

Journal: Reproductive BioMedicine Online

Publisher: Elsevier BV

Authors: Paula Vergaro, Gustavo Tiscornia, Montserrat Barragán, Désirée García, Amelia Rodriguez, Josep Santaló, Rita Vassena

Published: 2019-06-01

Everything You Need To Know

1

What exactly is the vaginal microbiota and why is it important?

The vaginal microbiota refers to the community of microorganisms, primarily bacteria, that reside in the female reproductive tract. It's essential for maintaining vaginal health. In the context of In-Vitro Fertilization (IVF), the composition of this microbiota, particularly the presence of specific Lactobacillus species, can influence the success rates of the procedure. Imbalances or the presence of bacteria associated with Bacterial Vaginosis (BV) have been linked to reproductive health issues.

2

What is Bacterial Vaginosis (BV) and how does it relate to IVF?

Bacterial Vaginosis (BV) is a condition characterized by an imbalance in the vaginal microbiota, often involving a decrease in Lactobacillus species and an increase in other bacteria. In the context of IVF, the study found that the overall presence of a BV-like environment did not directly prevent live birth in cycles using donor eggs. However, this does not mean that Bacterial Vaginosis is not of concern. The study highlights the complexity of the vaginal microbiota and the importance of its balance for reproductive health, as BV is still linked to other reproductive health concerns.

3

What is the significance of Lactobacillus species in the context of IVF?

Lactobacillus species are a type of bacteria that are commonly found in a healthy vaginal microbiota. These bacteria help maintain an acidic environment, which protects against harmful pathogens. The study found that the dominance of specific Lactobacillus species, particularly L. crispatus, correlated with higher live birth rates in women undergoing IVF with donor eggs. This finding suggests that the presence of certain Lactobacillus species plays a positive role in IVF outcomes, while the absence may present challenges.

4

What did the study specifically examine regarding the vaginal microbiota and IVF success?

The study investigated how the composition of vaginal microbiota, specifically the presence of Lactobacillus species and bacteria associated with BV, at the time of embryo transfer, impacts the live birth rates in women undergoing IVF with donor eggs. The researchers examined samples to identify different microbiota profiles and correlated these profiles with the success of the IVF cycles. The use of donor eggs allowed the researchers to isolate the impact of the vaginal environment, removing potential confounding factors like egg quality.

5

What are the implications of these findings for those undergoing IVF?

Optimizing vaginal health could potentially improve the odds of a successful IVF cycle, especially the enrichment of the vaginal microbiota with L. crispatus. While the presence of a BV-like environment may not automatically prevent live birth in donor egg IVF cycles, having a vaginal microbiota dominated by L. crispatus correlated with higher live birth rates. Future research may focus on ways to promote the dominance of beneficial Lactobacillus species to enhance IVF success and reproductive health, particularly through interventions aimed at modulating the vaginal microbiota composition.

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