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Endometrial Microbiome and Miscarriage

Written by
Clare Carrick ANutr (BHSc Nutrition and Health Promotion)

Scientifically reviewed by
Dr Fathalla Ali, PhD (Paediatrics)


Whilst there is plenty of buzz surrounding ‘gut health’ and the ‘gut microbiome’, a woman’s endometrial microbiome has not yet become mainstream dinner table conversation…However, with rapid advances in this area, and some potentially life-altering discoveries being made, you can expect to see, and hear, a lot more about this area of microbiome research in the future!


The What?!

The endometrial microbiome is a relatively new kid on the block in terms of microbiome research, really only coming into the spotlight in the last five or so years. Only 9% of a woman’s entire human microbiome is in the female reproductive tract, and as of yet, most of the research on this area has been on the vaginal microbiome (1). Traditionally the uterus, home to the endometrial microbiome, was believed to be sterile, but it is now thought that the endometrium houses a completely different assortment of microbes to that of the vaginal microbiome (1). 


Let’s take a look at what this might mean for the future of reproductive health…


The Endometrial Microbiome: A Clue to Infertility and Miscarriage?

In 2020, indicators of the potential importance of the endometrial microbiome came to light, after differences were observed in the endometrial bacteria of a woman prior to miscarriage, compared to week 4 of a successful full term pregnancy (1). In this study, the endometrial microbiome in the 4th week of the successful pregnancy had a less rich and diverse, Lactobacillus-dominant composition compared to the endometrial microbiome sample prior to the miscarriage (1). 


This link has been noticed before with studies comparing the endometrial microbiome of different women and their pregnancy outcomes (2).  What these researchers noticed was that women with a Lactobacillus-dominated endometrial microbiome was much more likely to experience successful implantation, pregnancy, and live birth, than the women with an endometrial microbiome not dominated by Lactobacillus (2). 


One theory is that an imbalance in the endometrial microbiome may be the cause of infertility in some women, and that correcting this imbalance may be the key to improving the chance of pregnancy success (3). We already know that an infection in the uterus can impair successful pregnancy implantation due to the accompanying inflammation and immune activation of the endometrium, so the idea that the composition endometrial microbiome itself would have an impact is not too big a stretch (3). 


What This Could Mean

Although it’s still early days, these findings lead to a deeper understanding of some of the potential causes for miscarriage and infertility, which may prompt the development of innovative, microbiome-targeted interventions and treatments designed to help people lower their risks and hopefully avoid these heartbreaking events (1).


Although these results are promising, it is important to acknowledge that the data on the endometrial microbiome and its microbial inhabitants were collected using a transcervical catheter, meaning there is a chance of contamination from ‘outsider’ bacteria, which could distort the results (1).


So far, only a few tests are available to assess endometrial microbiome composition, and, although promising, evidence for their benefit and accuracy is not quite there yet (3). The theory is that, if the endometrial microbiome is found not to be dominated by Lactobacillus, future treatments, involving bacterial elimination using antibiotics or uterine ‘lavage’ (a sort-of ‘bath’ for the uterus), probiotics, or prebiotics, could help to correct this microbial imbalance (3). 

At the moment, this is really a case of ‘watch-this-space’. The evidence for this style of treatment, and its success with reducing miscarriage and infertility, is only in its preliminary stages and not quite ready for widespread clinical recommendation just yet, but the future of this area of microbiome research certainly does look bright (3).

Keywords: Disease, Bifidobacteria, Diet/Nutrition,  Environment, Lifestyle



  1. Moreno I, Garcia-Grau I, Bau D, Perez-Villaroya D, Gonzalez-Monfort M, Vilella F, Romero R, Simon C. The first glimpse of the endometrial microbiota in early pregnancy. American journal of obstetrics and gynecology. 2020 Apr 1;222(4):296-305.
  2. Moreno I, Codoñer FM, Vilella F, Valbuena D, Martinez-Blanch JF, Jimenez-Almazán J, Alonso R, Alamá P, Remohí J, Pellicer A, Ramon D. Evidence that the endometrial microbiota has an effect on implantation success or failure. American journal of obstetrics and gynecology. 2016 Dec 1;215(6):684-703.
  3. Elnashar AM. Impact of endometrial microbiome on fertility. Middle East Fertility Society Journal. 2021 Dec;26(1):1-6.

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