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Preterm birth
Pregnancy Apr 16, 2020
6 Minutes

Can this help in the fight against preterm birth?

Here at The Journey we have been very focused on the latest pioneering research coming out around the gut and the vaginal (or reproductive) microbiome. Although in research terms, it is still early days, what looks increasingly clear is that this collection of bacteria, fungi and even viruses can have long term implications for the health of ourselves and of our children – click here for more on the gut. The latest research to catch our eye focuses on the balance of bacteria in our vaginas and how this can potentially impact our chances of avoiding preterm birth – by as much as 75%! Here is what you need to know: 

How can the balance of bacteria in your vagina impact birth outcomes? 

We have long known that the vagina has its own collection of bacteria. Interestingly enough, The Human Microbiome Project has estimated that the female reproductive tract microbiota accounts for approximately 9% of the total bacterial load. (5) To give you a sense of what that looks like: there are approximately 1bn bacteria per gram of vaginal fluid in a healthy vaginal microbiome! 

Quite a bit then!

Why does this matter when it comes to preterm birth? 

Research is also increasingly underlining that when things go wrong, there may be a link to this microbiome being ‘out of balance‘.

No, not only when we have a major bacterial infection which is obviously not ideal. The suggestion is that more subtle imbalances could play a part in challenges that some couples face. 

Here’s the interesting part:

Research recently released has found that ‘women with a normal vaginal microbiome had as much as a 75% lower risk for preterm birth and that the abundance of Lactobacillus was the strongest risk factor.’ (6)

So, what is ‘balance’ when it comes to the reproductive microbiome? 

It turns out, it is all about the bacteria family: Lactobacillus… 

Unlike the gut, where the science as it stands (and as a reminder this is all new, developing fast) suggests that we want as much diversity as possible with no imbalances. The reverse appears true when it comes to the female reproductive microbiome. Particularly when it comes to reducing risks of preterm birth. 

As much as 90%… 

In fact, recent research over the last couple of years has suggested that what you want is heavy dominance by Lactobacillus. As much as +90% of the bacteria in fact from this family.  This does vary depending on your time of life. It also appears to be somewhat dependent on your ethnicity (5). However, for reproductive age women, it is certainly the case that when it comes to having a healthy reproductive tract dominance of Lactobacillus is ideal.

The latest research is showing that during pregnancy it is even more important. In fact, it appears to actually naturally increases vs non pregnancy. (6) 

So what is preterm birth? 

Premature birth is defined as birth of a baby before 37 weeks gestational age. Sadly, is on the rise globally and is the leading cause of death in the early weeks following birth. (6) 

Spontaneous Premature Birth accounts for two thirds of all preterm birth but let’s be very clear from the start, it is a complex phenotype. It appears to be linked to a number of factors including previous premature birth, race, gum disease, low BMI, maternal stress and low socio demographic status. (6)

So, what is the connection to the vaginal or reproductive microbiome? 

New research is linking incidence of premature birth, particularly in the first and second trimester (2) to an imbalance in our vaginal microbiome Regardless of race or ethnicity (6). Specifically not having enough of that all important protective Lactobacillus. This of course can occur for a variety of reasons. 

Why is having a Lactobacillus dominated reproductive microbiome so important for reducing chances of preterm birth? 

Well, firstly Lactobacillus produces Lactic Acid. This reduces the pH to below 5 (ie. makes conditions more acidic). That means that other (undesirable) bacteria are less likely to be able to grow. (1, 4, 5) 

One of the crucial mechanisms behind this ‘protective’ factor appears to be its role reducing inflammation which has long been linked to preterm birth. 

‘Lactobacillus has been shown to reduce the pro-inflammatory molecules…while increasing secretion of anti-inflammatory cytokines’ (1)

Click here for a reminder why long term inflammation is not something we want. 

Preterm birth appears not only related to major infections: 

Of course we know that if there is a major infection this can cause all sorts of problems. However, it does appear to be a bit more subtle than this.

‘Dysbiotic deviations from the Lactobacillus dominant vaginal profile during pregnancy results in increased risk of miscarriage and preterm birth.’ (5) 

So what does this all mean? Most importantly what can we do in order to reduce our chances of preterm birth?

Well first and foremost, and being at risk for being a broken record (!) It is important to remember that as with the research around the gut microbiome, this research is still very much in its infancy. That’s being said, having a healthy reproductive tract is never going to be a bad thing. This research seems to further emphasise this.

We know serious bacterial infections will cause problems. However, this is suggesting more subtle imbalances away from the ideal, can also potentially contribute to challenges that many couples are facing. Click here for more relating to its role in miscarriage and implantation issues. 

How can you promote more Lactobacillus in the reproductive microbiome? 

Well once again there are no clear cut answers at this stage. However there are a few things that are being discussed.


We are increasingly realising that many over the counter, store bought probiotics may be a waste of money. Click here for more. However, what is looking increasingly interesting is targeted probiotic use. With specific strains for specific things. Click here for another example which appears to show targeted strains as useful for colic/reflux.  

In the case of the reproductive tract, it seems relatively clear that Lactobacillus domination is ideal. There are several oral and vaginal probiotics currently commercially available. (5)

The initial results are encouraging. One study showed benefits in terms of colonisation from one cycle of probiotic treatment between 10-60%. This appears to be dependent on the species of Lactobacillus and whether it was orally or vaginally administered. (1) This particular study highlighted Lactobacillus Rhamnosus as particularly beneficial. 

However. As with any of these things it is imperative that if you are going through any of these issues and would like to investigate further that you speak to your doctor first. Particularly if you are going through any treatment. 

What about from food? 

At this stage creating a healthier microbiome certainly seems to come via what you eat. In fact research suggests it can be changed in as little as 24hrs via what you eat. Click here for more. 

When it comes to Lactobacillus specifically, it is principally found in dairy and fermented foods: think Kefir, Sauerkraut and Sourdough bread (7). They have been used for generations.

Is this a silver bullet? 

Generally there are no ‘silver bullets’. The human body is complex. The good news is that even if you are faced with premature birth the latest research suggests there is a lot we can do to help with development. Click here for more. However, if we do what we can to get the body into balance and allow it to do its job then it cant be a bad thing. As always, speak to your doctor if you are concerned and before making any changes. 


1) Selection of new Probiotics for Endometrial Health: Frontiers in Cellular and Infection microbiology April 2019

20 Endometrial Microbiota: A new player in town. Fertility and Sterility July 2017. 

3) Evidence that the endometrial microbiota has an effect on implantation success or failure: American Journal of Obstetrics and Gynaecology. Dec 2016 

4) Characterisation of Microbiota in Endometrial Fluid and Vaginal Secretions in Infertile Women with Repeated Impantation Failreu: Mediators of Inflammation. 2019. 

5) Deciphering the effect of reproductive tract microbiota on human reproduction. Reproductive Medicine and Biology. Jan 2019.

6) Kosti I, Lyalina S, Pollard: Meta-Analysis of Vaginal Microbiome Data Provides New Insights Into Preterm Birth: Frontiers in Microbiology: April 2020

7) Bernardeau M, Guguen M, Vernoux JP: Beneficial Lactobacilli in food and feed: long-term use, biodiversity and proposals for specific and realistic safety assessments.


This article is for informational purposes only. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice. The information on this website has been developed following years of personal research and from referenced and sourced medical research. Before making any changes we strongly recommend you consult a healthcare professional before you begin.

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