3-min Science Digest · 31 May 2022

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In 10 seconds? Researchers have discovered how pregnancy rates, the success of assisted reproductive treatments, and favorable pregnancy outcomes are all linked to the dominance of a bacteria species in the female genital tract.

What? Bacteria have a say in pregnancy? Well, that’s what this study says after comparing the bacterial profile of the uterus and vagina of fertile and infertile women. Fascinatingly, the pregnancy rate was only 33.3% in females without a rich environment of Lactobacillus, compared to 70.6% in females with a high abundance of the bacteria (rate: 90% or more). In vitro fertilization (IVF) success of five participants in the study was also linked to the dominance of Lactobacillus in their bodies.

Why do bacteria play such an important role in pregnancy? The Lactobacillus species is very important in maintaining a healthy environment in the vagina. They maintain a low vaginal pH by producing lactic acid and other antimicrobial compounds to protect the sex organ from harmful pathogens and sexually transmitted diseases. These bacteria can also modulate the secretion of key molecules (inflammatory cytokines) that regulate biological processes in the body. The role of Lactobacillus in predicting the success of fertility is unclear, however, changes in cytokine levels were observed in women with preterm birth, thus offering potential interplay to pregnancy outcomes.

Number of pair samples with detection of most abundant operational taxonomic units (and highlighting to dominance of Lactobacillus) in vaginal aspirate alone (VA), endometrial fluid (EF) alone, and in both VA and EF. Source: Moreno, Codoner, Vilella et al, 2016

What happens if I have bacterial vaginosis and I’m considering IVF? Great question! It turns out that patients with bacterial vaginosis (inflammation due to disturbance in vaginal microflora) have a lesser rate of success with embryo implantation compared to patients with normal bacterial flora (27.6% vs 36.3%). However, this reduction is not considered significant. Although, bacterial vaginosis can also lead to a higher occurrence of preterm birth, low birth weight, and premature rupture of membranes.

Can tweak the levels of my bacteria? Probiotics have been considered to restore the dominance of Lactobacillus to improve pregnancy outcomes. In a preclinical study with female mice, probiotics reduced the presence of pro-inflammatory markers from bacteria that caused inflammation and promote the production of anti-inflammatory cytokines. The female mice were able to restore their fertility and deliver pups upon treatment with probiotics after inflammation. Obviously, this was a study done with lab animals. More studies and human trials are necessary to ensure the correct dose, treatment duration, and the matching of the right probiotics to bacterial strains.

I hear a lot about the gut microbiome. Is it linked to the vaginal microbiome? Yes! The Lactobacillus species in the vagina is also richly abundant in the gut, where it mediates key biological processes. ”Crosstalk” between the microbial species in these two organs has been identified. Boosting the gut microbiome has a positive impact on the vaginal microbiome, while bacterial vaginosis has been associated with poor gut health.

Bacteria do more than maintain healthy organs

Bacteria can also break down medications, causing them to become ineffective at times.

An HIV drug, tenofovir disoproxil (sold under the trade name Viread) had very different results in women, ranging from 49 to 75% efficacy in clinical trials.

A study looking at the role of vaginal microbiome on the drug’s activity showed that it reduced HIV infection by 61% in women with Lactobacillus dominant vaginal bacterial profile, but only by 18% in non-Lactobacillus (NLB) dominant women.

Further studies revealed the capabilities of the Gardnerella species (found in NLB women) to metabolize the drug, thus causing it to be ineffective against the HIV virus.

Microbiome research is growing at a fascinating rate as it plays an important role in regulating many of our body’s functions.

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The Science Integrity Check of this 3-min Science Digest was performed by 

Dr. Mónica Faut.

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