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Conception Pregnancy Oct 25, 2019
7 Minutes

Could the microbiome play a role in miscarriage, endometriosis, infertility?!

Here at The Journey we are not shy about talking (a lot) about the new science emerging around the power of the gut microbiome.Particularly for our purposes: hormones and development of the brain and immune system of a small person. One well known bacteria: Lactobacillus may play another important role…

In this article we are going to be talking about one of the latest discoveries around the microbiome. But, not the microbiome you may be thinking of…. ! 

Did you know that there is a reproductive tract microbiome?!

Well… there is. Turns out, just like the gut microbiome, it matters. Particularly, once again, for our purposes: having healthy kids. 

In fact….

The latest science is suggesting that getting that into the ‘right’ balance could be a positive step. Particularly when it comes to miscarriage, endometriosis and aiding implantation and a successful pregnancy.

Yes. Really.


Ok so here is what the latest science is suggesting – its pretty cool!

‘There is increasing evidence for microbiota as a key player not only in gynaecological health but also in pregnancy and for the infant.’ (1) 

So taking a step back.

What is a microbiome?

Well simply put it is a collection of bacteria, fungi and even viruses. The more ‘famous’ microbiome is the one within the gut. However, up and coming is the reproductive microbiome. 

We have long known that the vagina has its own collection of bacteria. More recently however, science has discovered that this extends up towards the upper reproductive tract. Including the uterus and endometrium. 

Interestingly enough, The Human Microbiome Project has estimated that the female reproductive tract microbiota accounts for approximately 9% of the total bacterial load. (5) 

This may give you a sense of how much bacteria we are talking about. There are approximately 1bn bacteria per gram of vaginal fluid in a healthy vaginal microbiome.

Quite a bit then!

Why does this matter?

We are also realising that when things go wrong, there may be a link to this microbiome being ‘out of balance‘. No, not just when we have a major bacterial infection which is obviously not ideal. It suggests that more subtle imbalances could play a part in challenges that some couples face. 

So what is ‘balance‘ in the case of the reproductive microbiome? All about Lactobacillus… 

Unlike the gut, where the science as it stands (and as a reminder this is all new, developing fast and we do not know it all yet) suggests that we want as much diversity as possible with no imbalances. It seems the reverse is true when it comes to the female reproductive microbiome.

In fact, recent research out over the last couple of years has suggested that what you want is heavy dominance by Lactobacillus. As much as +90% being made up of Lactobacillus. Which is a particular type of bacteria. 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. 

Why is having a Lactobacillus dominated reproductive microbiome important?

Well, 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) 

This appears to be favourable for embryo implantation for example (4). 

What happens if we don’t have enough Lactobacillus?

There is some evidence linking a lack of Endometrial Lactobacillus to those who struggle to become pregnant. Be that around implantation failure or even relating to those who suffer miscarriage. (1, 2 ) 

One of the reasons, according to the latest research, is around inflammation. It appears Lactobacillus plays a role reducing inflammation and encouraging implantation: 

‘Lactobacillus has been shown to reduce the pro-inflammatory molecules…while increasing secretion of anti-inflammatory cytokines… to prepare the endometrium for embryo implantation.’ (1) 

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.

Although, it is good to note that this is a ‘link’ at this stage. Rather than definitive cause. Always good to bear in mind….

Is there a connection between Endometriosis and the reproductive tract microbiome?

Endometriosis is a tricky one. It often doesn’t get diagnosed and question marks remain over what causes it. From a conception perspective, it can potentially make egg implantation and a viable pregnancy more challenging. 

The interesting part of this latest research is starting to suggest that people who suffer from Endometriosis have a different type of reproductive tract microbiota. The theories are that this altered microbiome could be a reason behind the inflammation. This may trigger the abnormal symptoms of endometriosis. (5) 

Now. Of course, as a reminder the science here is new and still developing. However, this is an interesting additional piece in the puzzle. Crucially something that you may be able to do something about.

What about miscarriage?

Of course there are multiple potential reasons behind miscarriage. Ranging from chromosomal abnormality (that means genetic issues with the egg/sperm). To the immune system misfiring, to serious bacterial infection being another of course. Click here for our discussion with leading miscarriage specialist Hassan Shehata. However, research is now also linking it to dysbiosis (ie. not what it should be) in the reproductive microbiome:

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

Once again. Many potential causes behind these things. However, another bit of food for thought…

What about women struggling with fertility?

As before, there are many drivers behind these issues. However, ‘evidence from several groups indicates that infertile patients harbour a different reproductive tract microbiota compared to healthy and fertile women.’ (3) 

It has also been suggested that a high percentage of people who are undergoing assisted reproductive technology have an ‘abnormal’ endometrial bacterial profile. (5)

So what does this all mean? Most importantly what can we do about this?

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. The 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. 

So, 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.

As one study suggested:

‘It is logical to hypothesise that the lower the number of bacterial pathogens in the reproductive tract and the higher the proportion of beneficial Lactobacillus could increase reproductive outcomes in those patients with abnormal microbiota.’ 


We are increasingly realising that many over the counter, store bought probiotics may be a waste of money. However, what is looking increasingly interesting is targeted probiotic use. With specific strains for specific things. Click here for another example. 

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 specifies of Lactobacillus and whether it was orally or vaginally administered. (1) 

This particular study highlighted Lactobacillus Rhamnosus as particularly beneficial. 

If there is ‘bad bacteria present’ what about antibiotics?

Obviously this is only ever a conversation to have with your doctor. Particularly as we have well documented issues around antibiotic resistance. Plus the lack of ‘targeted’ antibiotics meaning that the ‘good’ bacteria often gets taken out alongside the ‘bad’. On top of that it may not address the underlying issues. (1) 

However, in some cases, it has shown benefit in terms of pregnancy success. Particularly for people with endometriosis. Some research has shown it could even potentially be used in conjunction with probiotics following treatment. (5) 

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. 

Often there are no ‘silver bullets’. The human body is complex. However, if we can do what we can to get the body into balance and allow it to do its job then it cant be a bad thing!.

If you would like to read more on this research check out the links below.

  1. Selection of new Probiotics for Endometrial Health: Frontiers in Cellular and Infection microbiology April 2019
  2. 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. 


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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