On the way to motherhood, numerous agents and factors come together that can determine the success or failure of the journey to achieve pregnancy. One of the key players involved in this process is the microbiome, which has a close connection to reproductive health, especially in women.
For many people, this term may be unfamiliar, although they have likely heard of remedies that help alleviate its effects, such as probiotics. To better understand its functions and implications, let’s take a closer look at everything surrounding the microbiome.
What Is the Microbiome and What Are Its Functions?
According to the National Human Genome Research Institute, the microbiome is defined as the community of microorganisms (such as fungi, bacteria, and viruses) that exist in a particular environment. In humans, the term is often used to describe the microorganisms that live in or on a specific part of the body, such as the skin or the gastrointestinal tract.
Studies confirm that between 500 and 1,000 bacterial species inhabit the human body. This represents about 1–3% of total body mass, and they are essential for maintaining health.
This community of microorganisms performs vital tasks in the body: they break down food to extract necessary nutrients, educate the human immune system to recognize invading external agents, and even produce anti-inflammatory compounds and some vitamins. The microbiome also influences immune tolerance in the endometrium, affecting its receptivity in assisted reproduction processes and embryo implantation.
Types of Microbiomes That Influence Fertility
All the genetic material, arranged in sequence as a DNA chain, found in an individual microbe is referred to as the microbiome. It can affect fertility in various ways, and there are several types:
Vaginal Microbiome
The role of the microbiome in the vaginal area is to maintain an environment that supports successful fertilization. To achieve this, it is essential for a community of bacteria to coexist and keep the area healthy with the proper pH to receive sperm. The most common bacteria are known as lactobacilli. These microorganisms fight against harmful agents to prevent any type of genital infection. For this reason, maintaining a balanced population of these bacterial strains is important for improving, for example, the success rate of IVF treatments.
Endometrial Microbiome
It directly influences embryo implantation. Studies confirm that alterations in the endometrial flora due to intestinal dysbiosis (such as a lack of lactobacilli or an overgrowth of Candida) or sexually transmitted infections increase the risk of miscarriage and reduced fertility.
Gut Microbiome
It provides hormonal balance and is closely connected to the immune system. When a hormonal imbalance occurs, estrogens are not properly eliminated and return to the bloodstream. The bacteria responsible for eliminating estrogens (known as the estrobolome) can be altered—for better or worse—depending on lifestyle and dietary habits.
What Causes a Microbiota Imbalance?
An imbalance in the microbiota, known as dysbiosis, triggers an inflammatory state that ultimately disrupts immune activity. This heightened response can cause inflammation severe enough to lead to recurrent miscarriages and/or implantation failures.
The microbiota of a fertile woman is significantly different from that of an infertile woman. In a healthy woman, there is a high presence of Lactobacillus and Micrococcus species; in women with fertility issues, however, there is an overgrowth of dysbiosis accompanied by a minimal presence of lactobacilli.
Research has shown that an endometrial microbiome dominated by Lactobacillus is associated with a 60.7% implantation rate and a 70.6% pregnancy rate, compared to significantly lower rates in women whose microbiomes are not Lactobacillus-dominant.
These imbalances can be reduced and improved through different actions or habits, which we will explore in the next section.
How Can I Improve It? Recommendations
There are several ways to improve the body’s microbiome. Key recommendations include adopting a healthier lifestyle and diet, reducing stress levels, getting adequate rest, avoiding or minimizing a sedentary lifestyle, and limiting exposure to toxins. The use of probiotics is also recommended to enhance both intestinal and vaginal flora.
Probiotics are live microorganisms that help improve gut health when consumed. Some of the most notable sources include:
- Yogurt
- Kefir
- Kimchi
- Pickles
Tests to Evaluate the Microbiome
In addition to the many lifestyle and consumption habits that should be adjusted to drastically improve the overall microbiome, there are tests available to assess its condition and determine whether fertility issues may be linked to potential imbalances.
The most common microbiome tests for IVF are EMMA and ALICE.
EMMA test
It is a test that analyzes the bacterial composition of the endometrium—the inner lining of the uterus—to assess whether there is an adequate microbial balance for embryo implantation during an in vitro fertilization (IVF) treatment.
ALICE test
It is a diagnostic test that detects the most common pathogenic bacteria responsible for chronic endometritis, recommending the appropriate antibiotic and probiotic treatment. It is recommended for patients trying to conceive naturally who have experienced recurrent pregnancy loss.
If you want to understand the state of your microbiome or whether it may be affecting your specific case, don’t hesitate to consult a fertility specialist. This decision can be crucial in minimizing potential risks.
References
- Does probiotic and prebiotic treatement in ivf cycles of infertile women with Intestinal dysbiosis, affect pregnancy rate? Irollo a.m1, gangale m.f.1, tartaglione a.1, criscuolo c.2, aiello r.1, stortini e.1, infante v.1 1center for reproductive medicine chianciano salute via c. Marchesi 73
- Endometrial microbes and microbiome: Recent insights on the inflammatory and immune “players” of the human endometrium, Silvia D’Ippolito1,2 | Fiorella Di Nicuolo1,3 | Alfredo Pontecorvi3,4,5 | Matteo Gratta2 | Giovanni Scambia1,2 | Nicoletta Di Simone1,2
- National Human Genome Research Institute. (2025, 24 de junio). Microbioma. Talking Glossary of Genetic Terms. https://www.genome.gov/es/genetics-glossary/Microbioma
- Pastor, D. (2022). Microbiota y fertilidad en la mujer [Tesina]. https://didacpastor.com/wp-content/uploads/2022/12/Tesina-final.docx.pdf
- Tersigni, C., et al. «Recurrent pregnancy loss is associated to leaky gut: a novel pathogenic model of endometrium inflammation?». Journal of translational medicine 16.1 (2018): 102.
