The Vaginal Microbiome – the hidden key to success in IVF?

In vitro fertilisation (IVF) as the names suggests, is a fertility treatment where an egg is fertilised by a sperm outside of the body. For many couples diagnosed with infertility, IVF offers hope of conceiving a child.

The first IVF baby was born in July 1978. Yet, despite decades of technological advances, IVF success rates remain modest. In the UK, in 2023, the average pregnancy rate using frozen embryo transfers was 39% per embryo transferred and the average preliminary birth rate was 33% per embryo transferred^[1].

This raises an important question: why do some cycles fail even when everything appears to point to a successful outcome?

While multiple factors influence fertility, emerging research points to an unexpected factor - the vaginal microbiome.

What is the vaginal microbiome?

The vaginal microbiome, or vaginal microbiota, refers to a community of microorganisms, including bacteria, viruses and fungi, that live in the vaginal environment.

In healthy individuals, this environment is dominated by Lactobacillus species, which help maintain an acidic pH to protect against infections and inflammation. This protective role is crucial in preventing conditions such as bacterial vaginosis and yeast infections.

When this balance is disrupted, known as “dysbiosis”, harmful bacteria can thrive, leading to increased infection risk. Lifestyle factors are thought to play an important role in the shape of the vaginal microbiome, with factors such as diet and smoking having an effect on the level of Lactobacillus present.

The vaginal microbiome & IVF outcomes

Recent studies suggest that the composition of the vaginal microbiome may significantly impact IVF success. In particular, it is thought that Lactobacillus dominance is associated with better IVF outcomes – both higher rates of implantation and pregnancy success rates^[2].

Conversely, increased microbial diversity and dysbiosis have been linked to repeated implantation failure (RIF), recurrent pregnancy loss (RPL), and low IVF success rates, particularly in individuals with unexplained infertility (“idiopathic infertility”). Studies have identified an overrepresentation of genera such as Mobiluncus, Peptoniphilus, Prevotella, and Varibaculum in patients experiencing RIF^[3].

The future of IVF

According to Dr. Westphal in a recent webinar hosted by Evvy, unexplained infertility occurs in 30% of couples, and subset of these could be caused by issues associated with the vaginal microbiome. This makes it an important area for further research.

Advances in sequencing technology are enabling more precise identification of bacterial strains. Historically, 16S ribosomal RNA (rRNA) was used for screening studies, but sequencing based on fragments of the 16S rRNA gene (i.e., fragment based on the hypervariable regions) are generally considered not to provide strain-level specificity. However, more in-depth, strain-level information can be provided by using metagenomics to screen the vaginal microbiome in IVF patients to better understand the factors driving successful outcomes. In particular, researchers could look at strains and look at lifestyle factors to determine what can lead to unfavourable vaginal environments.

Companies like Evvy are aiming to transition patients from dysbiosis to Lactobacillus dominance by microbiome profiling to predict IVF success and personalise treatment plans.

Potential interventions could include, for example, microbiome-transplantation to restore a healthy vaginal microbiome and increase chances of a healthy pregnancy^[4]. Alternatively, more targeted probiotics or microbiome-based therapies may be used to improve implantation rates. For example, Zinereo Pharma's Fertibiome®, a probiotic solution based on Ligilactobacillus salivarius PS11610, has demonstrated antimicrobial and immunomodulatory activity. In clinical studies, Fertibiome® has been shown to significantly increase live birth rates in frozen embryo transfer cycles[5].

Patients now also have access to at-home vaginal microbiome screening kits from companies like Evvy and Daye, empowering them to understand and optimise their own microbiome.

A new frontier in fertility care

The vaginal microbiome’s role in IVF success is an exciting frontier. As research progresses, microbiome screening could become a standard step before IVF treatment. Integrating microbiome data into fertility care has the potential to revolutionise treatment strategies and improve outcomes for countless patients.

And of course, with all this potential for further research and innovation comes opportunities for new IP in this space. If you’d like to know more about IP relating to the vaginal microbiome, then please reach out to our Women’s Health team here at Mewburn Ellis.

References

1. [https://www.hfea.gov.uk/about-us/publications/research-and-data/fertility-treatment-2023-trends-and-figures/
2. García-Velasco, et al. The reproductive microbiome – clinical practice recommendations for fertility specialists. Reproductive BioMedicine Online, Volume 41, Issue 3, 443 – 453 (2020).
3. Xiuju Chen, et al., Implication of the Vaginal Microbiome in Female Infertility and Assisted Conception Outcomes, Genomics, Proteomics & Bioinformatics, Volume 23, Issue 4. (2025)
4. Meng Y, et al. Vaginal microbiota transplantation is a truly opulent and promising edge: fully grasp its potential. Front. Cell. Infect. Microbiol., (2024)
5. https://microbiomepost.com/beyond-the-gut-how-zinereo-pharma-is-redefining-reproductive-health/