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Vaginal Microbiome and IVF: What Lactobacillus Dominance May Mean for Implantation

Dr. Senai Aksoy · · Updated · 8 min read
Medically reviewed on 2 September 2026 - Dr. Senai Aksoy
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Key Takeaways

Observational studies link a Lactobacillus-dominant vaginal microbiome with better IVF outcomes, but they do not show that changing the microbiome improves implantation or live birth. Vaginal symptoms and recurrent bacterial vaginosis deserve standard clinical assessment; commercial vaginal or endometrial microbiome profiling is not recommended routinely, even after repeated implantation failure.

Key evidence: ESHRE Good Practice Recommendations on Recurrent Implantation Failure CDC STI Treatment Guidelines — Bacterial Vaginosis Reschini et al. 2022 — endometrial microbiome sampling and assessment

When the vaginal microbiome enters the IVF conversation

When IVF fails more than once, attention often goes first to embryo quality or endometrial thickness. Those factors matter. They are not the whole picture.

Research has found associations between vaginal microbial patterns and IVF outcomes in some patients. It has not shown that one microbiome pattern directly causes an embryo to implant or fail. Chronic endometritis is a separate diagnosis; a vaginal microbiome result does not diagnose it.

That is not a hidden key for every failed cycle. Symptoms or recurrent bacterial vaginosis deserve ordinary clinical assessment. A commercial microbiome profile is a different test, and the evidence does not support offering it routinely after implantation failure.

What a “healthy” vaginal microbiome usually means

In many women of reproductive age, protective Lactobacillus species dominate the vagina. Lactobacillus crispatus is the species most often linked with a stable, acidic environment.

L. crispatus produces lactic acid and helps keep vaginal pH below 4.5. A shift toward a more diverse community of anaerobic bacteria, which may include Gardnerella, Atopobium, or Prevotella, is often seen in vaginal dysbiosis and bacterial vaginosis. A sequencing result alone, however, does not diagnose bacterial vaginosis.

Why it may matter for IVF

The embryo is transferred into the uterus, not the vagina. Any effect is therefore indirect.

Dysbiosis has been proposed as a marker of local inflammation and altered immune signalling. Bacterial ascent and changes in endometrial immune tolerance are possible explanations, but they remain hypotheses rather than established causes of implantation failure.

Those links are biologically plausible. They are still being studied. A microbiome result should inform clinical judgement. It should not replace it.

Is there a separate uterine (endometrial) microbiome?

The uterine cavity is not a continuation of the vagina. Endometrial samples contain far fewer bacteria and rarely mirror vaginal Lactobacillus dominance (Reschini et al. 2022).

In a study that sampled endometrial fluid through embryo-transfer catheters, alongside matched vaginal swabs from the same women, Lactobacillus dominance appeared in only 8% of endometrial samples. The dominant bacterial genera matched between vagina and endometrium in only 8% of women.

Endometrial samples are also easy to contaminate with vaginal or cervical bacteria during collection. That is one reason researchers now prefer double-lumen catheters.

A low Lactobacillus percentage in an endometrial sample is not, on its own, proof of a problem. In an IVF cohort tested in parallel, pregnancy rates were similar between women labelled “dysbiotic” and “eubiotic” on endometrial testing, and some women conceived with no Lactobacillus detected in the biopsy (Hashimoto & Kyono 2019).

Which bacteria truly live in the uterus, which thresholds should count as normal, and whether changing that environment changes live birth remain open questions. That is part of why ESHRE’s 2023 recommendations on recurrent implantation failure advise against routine vaginal or endometrial microbiome profiling.

What the current data show

Several studies associate Lactobacillus dominance — especially abundant L. crispatus — with higher implantation or clinical-pregnancy rates. A recent systematic review reported the same overall direction, but its authors also acknowledged the low quality and risk of bias in the underlying evidence (systematic review and meta-analysis, 2025). These findings make the microbiome a research marker, not a treatment target.

The limits matter as much as the signal:

The microbiome is a useful research lead. It is not a shortcut, and it is not a guaranteed solution.

What should be evaluated, and when?

Vaginal symptoms should be evaluated, but that does not automatically mean microbiome sequencing.

Odour, irritation, unusual discharge, or recurrent bacterial vaginosis call for a clinical history and standard diagnostic testing as appropriate. Suspected chronic endometritis is a separate question and may warrant its own assessment.

For recurrent implantation failure, ESHRE does not currently recommend routine uterine or vaginal microbiome profiling. The same applies before a first, uncomplicated IVF cycle.

How to support a healthy vaginal microbiome

There is no standardised way to “raise” a Lactobacillus percentage the way one corrects a vitamin level. The practical steps are simpler: avoid products that disrupt the vaginal environment and treat a diagnosed infection appropriately. Do not use probiotics as self-prescribed IVF preparation.

  1. Avoid vaginal douching, scented wipes, antiseptic washes, and harsh soaps.
  2. Seek assessment for odour, irritation, unusual discharge, or recurrent BV rather than starting a probiotic alone.
  3. Stop smoking if you smoke.
  4. Use antibiotics or antifungals only when a clinical infection is diagnosed.
  5. If you are considering a probiotic, discuss the specific product and clinical reason with your clinician; an IVF benefit has not been established.
  6. Do not apply food products such as yoghurt into the vagina.

CDC STI guidance still concludes that, despite studies of intravaginal lactobacilli and other probiotic formulations for bacterial vaginosis, “no studies support the use of these products as adjunctive or replacement therapy in women with bacterial vaginosis.”

One randomised study of women recovering from bacterial vaginosis reported changes in vaginal health after oral probiotics were added to antibiotic treatment. It was not an IVF-outcome trial and excluded women who were pregnant or planning pregnancy, so it cannot show that probiotics improve implantation or live birth (Qi et al., 2023).

Whether oral probiotics can shift a low-Lactobacillus vaginal profile specifically in IVF patients is being studied in a placebo-controlled randomised trial. The cited publication is the study protocol, not a results paper (van Haren et al., 2025).

Dr. Aksoy’s clinical perspective

Lactobacillus is protective in the vagina, but treating a low reading with probiotics is not a simple vitamin fix. Active bacterial vaginosis requires antibiotics, not probiotics.

The uterine cavity is a distinct environment with far fewer bacteria. Reaching a specific endometrial Lactobacillus percentage is not a standard IVF target. I treat diagnosed clinical conditions and the patient in front of me — not a commercial microbiome score.

Request a case review

If you have recurrent bacterial vaginosis, repeated implantation failure, or a vaginal or endometrial microbiome result you are unsure how to use, a structured review can separate symptoms that need standard testing from results that may not change treatment.

You can request a confidential case review before deciding on next steps.

FAQ

Should every IVF patient test the vaginal microbiome?

No. ESHRE does not recommend routine vaginal or uterine microbiome profiling, even after recurrent implantation failure. Symptoms such as odour, irritation, unusual discharge, or recurrent bacterial vaginosis call for standard clinical assessment, not automatically for microbiome sequencing.

Is Lactobacillus crispatus always “good”?

It is generally a favourable sign, because it is associated with a more stable, acidic vaginal environment. A single microbiome result still has to be read together with symptoms and fertility history.

Can probiotics improve IVF success?

We do not yet know that they improve implantation or live birth. They should not replace diagnosis and targeted treatment when an infection is suspected.

They are separate clinical questions. Some inflammatory and bacterial findings have been studied in both, but a vaginal microbiome pattern neither proves nor diagnoses chronic endometritis. Suspected chronic endometritis requires its own assessment.

Should antibiotics be used before every embryo transfer?

No. Antibiotics should be used when there is evidence of infection or another specific indication. Routine, untargeted use is not a good strategy.

Sources

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Dr. Senai Aksoy

Dr. Senai Aksoy studied and trained in France before returning to Turkey, where he was a member of the ICSI team at Sevgi Hospital, Ankara — the country's first ICSI centre (1994-95) — and a co-author on the first Turkish ICSI publications produced in collaboration with the Brussels Van Steirteghem group (Human Reproduction, 1996; PMID 8671323). He helped build the IVF programme at the American Hospital Istanbul and has been running his own fertility practice since 1998.

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