Miscarriage: what if the vaginal microbiome was involved?

Currently, no treatment exists to prevent miscarriage, which affects 20% of pregnancies during the first trimester. English researchers took an interest in the vaginal microbiome of these future mothers and concluded that a modification of the bacteria present could be responsible for miscarriages. Their results were published on January 22 in the journal BMC Medicine.

A study conducted on 167 pregnant women

Scientists studied the cases of 167 women who had already had a miscarriage or experienced bleeding or pain during the first trimester of their pregnancy, between March 2014 and February 2019. Participants who had taken antibiotics, probiotics or progesterone supplements at the time of sample collection were not included in the study as this may have altered their vaginal microbiome.

Of these 167 women, 93 miscarried and 74 delivered at term. Of the 93 women who miscarried, 54 had no chromosomal abnormality in the embryo that could explain the miscarriage.

The researchers examined the vaginal bacteria present in all of these women, as well as looking for molecular signs of inflammation.

Pathogenic bacteria found

In women with chromosomally “normal” miscarriages, researchers found a reduced number of lactobacilli in their vaginal microbiome compared to women with chromosomally abnormal miscarriages.

The researchers also found high levels of inflammation in those women who had bacteria such as Prevotella and Streptococcus instead of Lactobacilli. Conversely, some women who gave birth at term had reductions in lactobacilli, but their immune system did not react to this and did not cause inflammation.

According to the researchers, miscarriages could be linked to inflammation, caused by a change in the vaginal microbiome. “There are several ideas as to how this inflammation could lead to pregnancy loss such as certain vaginal bacterial organisms triggering inflammation upstream which causes the lining of the uterus to break down.”says Dr. Karen Grewal, lead author of the study.

The Importance of a Healthy Vaginal Microbiome

Conversely, when there are no bacteria creating this inflammation, the vaginal microbiome is healthy. It limits infections, thanks to the lactobacilli that compose it and which will produce lactic acid to counter any bacteria that can cause infections. When, due to an imbalance in the vaginal microbiome, there are too few lactobacilli, there is local inflammation which would increase the risk of miscarriages.

The researchers believe their findings suggest a potentially treatable cause of miscarriage, but acknowledge that further research is needed to first confirm the association.

Influencing the vaginal microbiota to reduce the risk of miscarriage

According to the release from Imperial College London, researchers are working on a new test to quickly analyze the vaginal microbiome, as they believe it could help identify women who could benefit from preventative treatment for miscarriage. However, there is currently no way of knowing whether modifying the vaginal microbiome would reduce this risk.

But if the vaginal microbiota and risk of miscarriage link is confirmed, the main author Pr. Phillip Bennett judges that “this could highlight the important role of good vaginal hygiene in early pregnancy. For example, it may be a good idea to wash regularly, but avoid scented soaps, gels and antiseptics, as we know they can affect the healthy balance of bacteria and acid levels in the vagina. Douching is best not to use as it can disrupt normal vaginal bacteria”.

But he remains cautious: “Our early findings don’t give us enough information to say there’s a link between these types of products and miscarriage, but they do suggest that we need to take a closer look at the role of the vaginal microbiome.“