Mazen Al-Obaidi: The Hidden Ecosystem That May Shape Your Fertility

“The reproductive microbiome is the community of bacteria that lives in the vagina and the womb, and it is linked to the chance of pregnancy. For years, the womb was thought to be sterile (Stoyancheva et al., 2025). Research now shows it holds a small but active set of bacteria that are linked to embryo implantation and IVF success. This article explains what the reproductive microbiome is, how it affects fertility, and what recent studies show about changing it.

What is the reproductive microbiome?

The microbiome is the full set of bacteria that live in a part of the body. In the female reproductive tract, one group matters most:

• A healthy profile is dominated by Lactobacillus, a protective bacterium that keeps the environment slightly acidic (Stoyancheva et al., 2025; Hiratsuka et al., 2026).
• Lactobacillus crispatus is the species most often linked to good reproductive outcomes (Du et al., 2026; Burkova et al., 2026).
• An unhealthy profile, called dysbiosis, means low Lactobacillus and overgrowth of other bacteria such as Gardnerella, Atopobium, Prevotella, and Streptococcus (Stoyancheva et al., 2025).

Dysbiosis means the loss of the protective balance. It raises inflammation in the lining of the womb (Li et al., 2026).

How does the reproductive microbiome affect fertility?

The balance of bacteria tracks closely with reproductive success:

• A Lactobacillus-dominant profile is linked to higher implantation and pregnancy rates in IVF (Peng et al., 2025; Stoyancheva et al., 2025).
• Dysbiosis is linked to chronic endometritis, repeated implantation failure, and recurrent pregnancy loss (Hiratsuka et al., 2026).
• The species matters. Lactobacillus crispatus tracks with success, while Lactobacillus iners appears in both healthy and unstable profiles (Hanaoka et al., 2025; Burkova et al., 2026).
• During pregnancy, a Lactobacillus-rich vaginal profile is linked to lower risks of miscarriage and preterm birth (Hiratsuka et al., 2026).

The link works through the immune system and the barrier of the womb lining. Protective bacteria produce lactic acid, support the barrier, and calm inflammation, which helps an embryo implant (Li et al., 2026).

Does changing the microbiome improve fertility?

This is the active research question, and the early answers are mixed but promising:

• A ‘test and treat’ approach uses antibiotics, often with vaginal Lactobacillus probiotics, to restore balance. It has been reported to improve implantation in selected patients (Hiratsuka et al., 2026).
• In one clinic study, treating women with an unhealthy endometrial profile raised their pregnancy rates toward those of women who started with a healthy profile (Hanaoka et al., 2025).
• In a small, preliminary 2025 randomised trial, an oral probiotic (Ligilactobacillus salivarius) raised pregnancy rates to 48% versus 20% with placebo in couples with unexplained infertility before IVF (Huerga López et al., 2025).
• Tests such as ReceptIVFity read the vaginal profile to estimate the chance of pregnancy before IVF (Koedooder et al., 2019; van Haren et al., 2025).

What are the limits and cautions?

The science is young, and the evidence is not yet settled:

• The womb holds very few bacteria, so samples are hard to measure and easy to contaminate (Stoyancheva et al., 2025; Burkova et al., 2026).
• Probiotic results differ across studies, and no standard protocol exists (Du et al., 2026; Burkova et al., 2026).
• Large randomised trials that measure live birth as the main outcome are still needed (Du et al., 2026).
• Microbiome testing and probiotic treatment are not yet routine parts of IVF care (Burkova et al., 2026).

This article is for general information only and is not medical advice. Please speak to a doctor or fertility specialist about your own situation.”

Written by Mazen Al-Obaidi

Assistant Professor, University of Technology and Applied Sciences

References

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You can read the Full Article in the European Journal of Obstetrics, Gynecology, and Reproductive Biology.

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You can read the Full Article in the Journal of Assisted Reproduction and Genetics.

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You can read the Full Article in Fertility and Sterility.

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Title: Human embryo implantation: The complex interplay between endometrial receptivity and the microbiome

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You can read the Full Article in the Journal of Reproductive Immunology.

Title: Endometrial Microbiome and Reproductive Receptivity: Diverse Perspectives

Authors: Galina Stoyancheva, Nikolina Mihaylova, Maria Gerginova, Ekaterina Krumova

You can read the Full Article in the International Journal of Molecular Sciences.

Title: ProVag: the effect of oral probiotics on the vaginal microbiota composition in women receiving medical assisted reproduction in a Dutch fertility clinic – protocol of a randomised, placebo-controlled, double-blind study

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You can read the Full Article in BMJ Open.

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