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How does the microbiome influence fertility?


The microbiome, or microbiomes, exist everywhere, inside us and around us. They are sometimes called our “second genomefor the direct relationship with our own genetics. A microbiome is a community of microorganisms which are found on all our body surfaces, such as the mouth, intestines, uterus, vagina, skin and the eyes. It is formed by, fungi, yeasts, archae, viruses but the main component is bacteria. The microbiota is the name given to all of the living microorganisms found in the microbiome.

In assisted reproduction, the microbiome, or endometrial flora (rich in Lactobacillus) is the collection of microorganisms that are found in the endometrium, the place where the embryo implants to begin a pregnancy. Many studies have demonstrated that the presence or predominance of certain bacteria can cause inflammation of the endometrium (chronic endometritis) recurrent implantation failures and failed pregnancies.

Furthermore, clinical cases have shown that a study of the endometrial microbiome, before the transfer, is a useful positive biomarker to be able to program or delay the embryo transfer.


Frequent gynecological infections or conditions, such as bacterial vaginosis, are related to changes in the vaginal flora. These can manifest in more abundant vaginal discharge, which may have an unpleasant odor, although they can also be completely asymptomatic. It has also been demonstrated that changes in the vaginal flora can be related to changes in the endometrial flora and result in endometritis, which is an inflammation of the endometrium. Due to the relationship between germs that produce inflammation, and the molecules that the immune system generates in response, the result can be a reduction in endometrial receptivity.

Reproductive problems, such as sterility, implantation failures (where after two or three transfers, pregnancy is not achieved), non-viable pregnancies such as biochemical pregnancies and miscarriages can be related to alterations in the endometrial microbiome.

Tests exist to help determine if the bacteria present in the endometrium are suitable for pregnancy to occur. These tests, developed by a clinical analysis laboratory, analyze the endometrial microbiome to determine if it is optimal or not, and detect any pathological

Changes in the semen analysis can also be responsible for an imbalance in the microbiota, such as a lower concentration of sperm, slower sperm, or semen analyses showing a high concentration of inflammatory cells.


To encourage a endometrium rich in Lactobacillus bacteria, you can eat a diet rich in pre and probiotics. Some foods containing these are natural yogurts, kefir, fermented soy products, and some fermented pickles such as gherkins or olives. Additionally, it is also recommended to have a diet rich in fibre: for example with wholegrain cereals, fruits and raw vegetables.

Probiotics and prebiotics also offer multiple benefits at other levels, especially in the support of intestinal flora, helping in the treatment of acute diarrhea, improving symptoms of irritable bowel syndrome and supporting a correct digestion in general, amongst other advantages.

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