By Gabrielle Gleeson-Solomon, CEO of Tota
Scientific Review by Dr Nick Parkinson, PhD
What the science says about vaginal microbiome and fertility—and what's still unknown.
The short answer is quite possibly. The longer answer is that the science is still incredibly new, and nobody should be selling you certainty on this one.
Around 1 in 6 people worldwide experience infertility at some point in their lives. We already know fertility is influenced by a complex mix of factors, from hormones and ovulation to egg and sperm quality. But researchers are now asking whether another piece of the puzzle could be the vaginal microbiome.
We don't yet have evidence that an imbalanced vaginal microbiome directly causes infertility. What we do know is that women with healthier vaginal microbiomes tend to have better fertility outcomes, particularly during IVF. Studies have linked healthier vaginal microbiomes with higher implantation, clinical pregnancy rates and lower rates of miscarriage in some cases.
The vaginal microbiome is one of the few factors influencing reproductive health that most women have never had the opportunity to measure.
Here's what we know, what's starting to emerge, and what nobody can tell you yet.
Why vaginal microbiome research is still so new
Until recently, hardly anyone was looking at the vaginal microbiome at all.
Women's health has historically been under-researched, and the vaginal microbiome is no exception. The first breakthrough came in 1892, when German gynaecologist Albert Döderlein identified a family of bacteria now known as Lactobacillus. He found they keep the vagina slightly acidic, making it difficult for harmful bacteria to thrive.
For more than a century, that was roughly where our understanding stopped.
It wasn't until advances in DNA sequencing over the last 15 years that scientists could see the vagina isn't home to just one family of bacteria. It's a whole ecosystem of bacteria, fungi and other microorganisms.
That changed the direction of research. Instead of focusing only on infections, scientists began exploring how the whole vaginal microbiome might influence women's health more broadly, including its potential role in fertility.
How the vaginal microbiome and fertility might be linked
A consistent pattern has emerged, although the evidence is still evolving. Women whose microbiomes are dominated by Lactobacillus bacteria tend to have better reproductive outcomes than women with less protective profiles.
Researchers have several theories about why this link exists. Three of the strongest are:
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Protecting the reproductive tract
Lactobacillus bacteria produce lactic acid, which keeps the vagina slightly acidic. That makes it harder for harmful bacteria to take hold or travel further into the reproductive tract. Researchers think this may help create a healthier environment for conception.
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Creating better conditions for sperm
For pregnancy to happen, sperm need to survive the journey to the egg. The vaginal environment needs to strike a careful balance: acidic enough to keep harmful bacteria under control, but still able to support sperm as they continue their journey towards the egg.
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Reducing the risk of imbalances like bacterial vaginosis (BV)
When Lactobacillus becomes less dominant, other bacteria take over. This is called vaginal dysbiosis and its most common form is bacterial vaginosis, or BV. Because BV has been linked to poorer reproductive outcomes, researchers are investigating whether preventing these imbalances could also support fertility.
What the research actually shows
Over the last few years, researchers around the world have compared the vaginal microbiomes of thousands of women with their fertility outcomes. Individual studies don't always agree, but one finding keeps coming up: women with Lactobacillus-dominated microbiomes generally have better outcomes, particularly during IVF.
A 2025 review of eight studies found that women with a more balanced vaginal microbiome had higher pregnancy rates, higher live birth rates and fewer miscarriages during IVF. Lactobacillus crispatus was the species most consistently linked to success.
A much larger review of 6,835 women undergoing IVF found that vaginal imbalance was associated with lower clinical pregnancy rates and a higher risk of early pregnancy loss. It showed up in around 19% of the women studied. That same review found no clear effect on live birth rates, which the researchers themselves called puzzling.
The vaginal microbiome is just one piece of the fertility puzzle. If you're wondering what else is worth checking before trying to conceive, we've put together a guide to the fertility tests that might be useful if you’re planning to or trying to conceive.
Can BV affect fertility?
Same answer. Quite possibly.
BV is common. The World Health Organisation estimates it affects 23 to 29% of women of reproductive age at any point in time. It's also often silent. In one large survey, 84% of women who met the diagnostic criteria for BV reported no symptoms at all. No odour, no discharge, nothing you'd think to mention to a GP.
BV has been linked to several reproductive complications, including pelvic inflammatory disease, miscarriage and preterm birth. That doesn't mean BV causes fertility problems. It does explain why it's become such an important area of research.
What we can say is that BV isn’t just about symptoms such as odour or discharge. BV has been linked to several reproductive complications, which is why researchers are investigating.
What we still don’t know
Despite the uncertainty, the vaginal microbiome is important. Researchers are investigating exactly how the vaginal microbiome influences fertility and which interventions could make the biggest difference.
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How much the vaginal microbiome affects fertility
Almost every study in this area is observational. Researchers record what's living in a woman's vaginal microbiome, then see what happens next. That shows the two things often appear together. It doesn't show that one caused the other.
A suboptimal vaginal microbiome might be making conception harder. Or something else, like inflammation, hormones or an existing reproductive condition, might be causing both. We just don’t know the exact cause and effect yet.
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Exactly which bacteria matter most
Lactobacillus crispatus bacteria consistently looks good. Beyond that, it gets messy. A 2026 study found that sorting women into the broad microbiome groups researchers usually use didn't predict IVF outcomes at all. Instead, two specific bacteria, Ureaplasma parvum and Lactobacillus iners, were associated with poorer implantation, clinical pregnancy and live birth rates.
Nobody has agreed on the culprit yet, or how much of it counts as too much.
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Whether improving the vaginal microbiome improves fertility
This is the big one, and it's where a lot of the internet gets ahead of the evidence. Correcting an imbalance and improving fertility are two different things.
In one trial, women given Lactobacillus before an IVF embryo transfer were no more likely to get pregnant than the women who weren't. Their miscarriage rate was lower, which is encouraging. Larger studies are still needed before we know exactly how much difference treatment can make.
What is in your control
While researchers continue answering these questions, one thing is within your control: understanding your own vaginal microbiome before you start trying for a baby.
Fertility investigations and treatment can be time-consuming, emotionally demanding and, for many people, expensive. A vaginal microbiome test isn't a replacement for conventional fertility testing, but it can provide additional information about an aspect of reproductive health that isn't routinely assessed. It's a simple, non-invasive way to check for microbial imbalances before moving on to more complex fertility investigations or treatment.
Because vaginal microbiome imbalances are often completely symptomless, many women have no reason to suspect anything is different. A microbiome test is one of the only ways to understand what's there and whether your microbiome appears to be in a healthy, Lactobacillus-dominant state. If an imbalance is identified, there may be simple and practical steps you can discuss with your healthcare professional, from lifestyle changes and probiotics to treatment where appropriate, before you start trying to conceive.
So, can the vaginal microbiome affect fertility?
Quite possibly, yes.
A Lactobacillus-dominant vaginal microbiome is associated with better fertility outcomes, particularly during IVF. A disrupted vaginal microbiome has been associated with poorer fertility outcomes. The mechanism isn't nailed down, the treatment pathway isn't fully proven, and anyone telling you otherwise is running ahead of the evidence.
If you're planning a pregnancy, understanding your vaginal microbiome won't give you all the answers, but it can give you information that would otherwise remain invisible. If you're looking to be as informed as possible before trying for a baby, that's a valuable place to start.
Know your body, totally.
There are a lot of fertility tests sold online. Some are worth doing, some aren't. We've written a separate guide on how to tell the difference.
Sources
- World Health Organization. 1 in 6 people globally affected by infertility. WHO; 2023. WHO
- Skafte-Holm A, Humaidan P, Bernabeu A, Lledo B, Jensen JS, Haahr T. The Association between Vaginal Dysbiosis and Reproductive Outcomes in Sub-Fertile Women Undergoing IVF-Treatment: A Systematic PRISMA Review and Meta-Analysis. Pathogens. 2021 Mar 4;10(3):295. PubMed 33806442
- Ventolini G. Progresses in vaginal microflora physiology and implications for bacterial vaginosis and candidiasis. Womens Health. 2016;12:283-291. PubMed 27215488
- Samama M, Ueno J, Carvalho de Arruda Veiga E, Piscopo RCCP, Ikeda F, Pires de Lemos N, Tadeu Bidinotto L, Guimarães da Silva M, Jarmy Di Bella Z, Entezami F. Vaginal Microbiome and Its Relationship with Assisted Reproduction: A Systematic Review and Meta-Analysis. PubMed 41010324
- Maksimovic Celicanin M, Haahr T, Humaidan P, Skafte-Holm A. Vaginal dysbiosis - the association with reproductive outcomes in IVF patients: a systematic review and meta-analysis. Curr Opin Obstet Gynecol. 2024 Jun 1;36(3):155-164. PubMed 38597377
- World Health Organization. Bacterial vaginosis. WHO Fact Sheets. WHO
- Koumans EH, Sternberg M, Bruce C, McQuillan G, Kendrick J, Sutton M, Markowitz LE. The prevalence of bacterial vaginosis in the United States, 2001–2004; associations with symptoms, sexual behaviors, and reproductive health. Sex Transm Dis. 2007;34(11):864-869. PubMed: 17621244
- Graspeuntner S, Lupatsii M, Hamala N, Masuch A, Depenbusch M, Pfeffer I, Schultze-Mosgau A, Eggersmann TK, Rupp J, Griesinger G. Vaginal microbial community state types fail to predict IVF outcomes, whereas Ureaplasma parvum and Lactobacillus iners are negative predictors of implantation, clinical pregnancy, and live birth. Hum Reprod Open. 2026;2026(2):hoag018. Oxford Academic
- Thanaboonyawat I, Pothisan S, Petyim S, Laokirkkiat P. Pregnancy outcomes after vaginal probiotic supplementation before frozen embryo transfer: a randomized controlled study. Sci Rep. 2023;13(1):11892. Nature
This article is for general information and does not replace medical advice. If you're experiencing new, severe, persistent or worsening symptoms, please speak to a GP or another qualified healthcare professional.
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