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Can a healthy microbiome prevent miscarriage?

Can a healthy microbiome prevent miscarriage?

Nicole Knight, AHCJ | March 27, 2020 | Getting Pregnant
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Miscarriage is common, occurring in at least one in four pregnancies. Medical experts generally agree that chromosomal problems account for around half of these pregnancy losses, but the reason for the other 50% is mostly unknown (1). 

Now science suggests that an unbalanced vaginal microbiome may play a role in miscarriage, and conversely, a balanced vaginal ecosystem may prevent miscarriages in the first trimester (1). 

The advantages of a healthy vaginal microbiome also appear to safeguard against preterm birth and include fertility benefits (2, 3).

Whether you’re trying to conceive (TTC) now — or down the road — here is what you need to know about keeping your vaginal microbiome healthy. We explain how the makeup of your microbiome may yield important clues about the likelihood of having a miscarriage or a healthy pregnancy, and whether modern medicine has come up with an evidence-based treatment for an imbalanced microbiome.


What's a vaginal microbiome?

The term microbiome is often used in reference to gut health. A vaginal microbiome is the same basic concept, except of course, in your vagina. 

The vagina is naturally colonized by a host of tiny microbes which make up the vaginal microbiome (4, 5). 

The amount and type of microbes in the vagina vary, but the majority are a helpful bacteria known as Lactobacillus. One study found that one or more species of Lactobacillus accounted for 73% of the vaginal bacteria in women of reproductive age (4). 

Lactobacillus perform an important job in the vagina. They churn out antimicrobial agents, such as lactic acid, to ward off pathogens that may cause infections and pregnancy complications (4, 5).


What affects Lactobacillus?

It’s not entirely clear why some women’s microbiomes contain more Lactobacillus than others. Scientists theorize that rising estrogen levels appear to trigger the cells lining the vagina to produce glycogen, which creates a welcoming environment for Lactobacillus to develop and flourish (4, 5). 


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What’s the role of the vaginal microbiome?

The quantity and type of bacteria in the vaginal microbiome is directly related to reproductive health. As a recent paper in Nature noted, “the hallmark of health in the female reproductive tract” is a homogeneous Lactobacillus-dominated vaginal microbiome (6).

Science shows that a healthy vaginal microbiome seems to protect against infections, such as bacterial vaginosis, yeast infections, sexually transmitted infections, and urinary tract infections (2, 6). 

The opposite also appears to be true. Research has linked a vaginal microbiome with low levels of Lactobacillus to an increased risk for pelvic inflammatory disease and even pregnancy complications (2, 6).


What does the vaginal microbiome have to do with pregnancy?

Research has shown that women with healthy pregnancies have vaginal microbiomes that are rich in Lactobacillus. High levels of vaginal Lactobacillus in pregnancy protect against genital infections, which are a common cause of miscarriage, notes a PLOS One study (2). 

Conversely, research has linked lower amounts of vaginal Lactobacillus to pregnancy complications, such as premature rupturing of membranes (amniotic sac) and preterm birth. This is crucial knowledge from a fetal health standpoint because preterm birth is the leading cause of neonatal death globally (2).


Does the uterine microbiome affect fertility?

Researchers are just beginning to explore how the composition of bacteria in the entire reproductive tract, not just the vagina, affects fertility. 

A small study in the American Journal of Obstetrics and Gynecology followed 31 women undergoing in vitro fertilization (IVF) and found that women with mostly non-Lactobacillus microbes in their uterine lining had significantly lower rates of implantation, pregnancy, and live birth than women with a uterine microbiome comprised of more than 90% Lactobacillus (3). 

The authors further found that women with uterine microbiota less than 90% Lactobacillus also had higher miscarriage rates (3). Findings like this have led some scientists to also investigate the role of the vaginal microbiome in miscarriage. 

Some researchers are even rallying behind a new theory — that the makeup of the vaginal microbiome early in pregnancy may be one of the most useful predictors of pregnancy-related complications, even miscarriage (1).


What does the vaginal microbiome have to do with miscarriage?

Scientists are now investigating the influence of a healthy — and unhealthy — vaginal microbiome during the first trimester, a crucial period of pregnancy when the majority of miscarriages occur (1).

A team of researchers in the United Kingdom and Belgium recruited a group of 161 women who were in their first trimester of pregnancy. The team took a series of samples of the women’s vaginal flora, compared it against a control group, and found that women who experienced first trimester miscarriages had significantly less Lactobacillus in their vaginal microbiome than women who went on to have full-term pregnancies (1). 

As the authors noted, the vaginal microbiome may be a “modifiable risk factor” in miscarriage — meaning that promoting a vaginal microbiome rich in Lactobacillus could potentially lower the risk of an early miscarriage (1).


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Similarly, a separate paper published in 2019 found that women who'd experienced at least 3 miscarriages for previously unknown reasons had imbalanced vaginal flora. The study found these women had less Lactobacillus in their vaginal microbiome than expected, and instead had an abundance of other microbes, such as Atopobium, Prevotella, and Streptococcus (7). 

The authors suggest that restoring a healthy vaginal microbiome through lifestyle changes, medications, or probiotics might potentially prevent pregnancy loss in the crucial early weeks of pregnancy (7).   


Do vaginal microbiome treatments work?

This is a question that scientists are still investigating. Certain oral vaginal probiotics appear to restore microbial harmony and reduce urogenital infections. However, the studies showing these benefits only included women who weren’t pregnant, so the data isn't useful in understanding whether probiotics might help prevent an early pregnancy loss (8). 

Researchers are now turning their attention to studying how oral probiotics may promote a healthy pregnancy, but unfortunately, a randomized trial last year found that taking an oral probiotic made no difference in the vaginal microbiomes of pregnant women (9).

The bottom line is that it’s too early to determine whether probiotics might one day prevent early miscarriages and promote healthy pregnancies; more research is needed.

If you’re trying to conceive, talk with your healthcare provider about the benefits and risks of probiotics before making the supplements a part of your fertility regimen.


  1. Al-Memar, M., Bobdiwala, S., Fourie, H., Mannino, R., Lee, Y. S., Smith, A., Marchesi, J. R., Timmerman, D., Bourne, T., Bennett, P. R., & MacIntyre, D. A. (2020, January). The association between vaginal bacterial composition and miscarriage: A nested case-control study. BJOG: An International Journal of Obstetrics and Gynaecology, 127(2), 264–274. https://doi.org/10.1111/1471-0528.15972
  2. Farr, A., Kiss, H., Hagmann, M., Machal, S., Holzer, I., Kueronya, V., Husslein, P. W., & Petricevic, L. (2015, December). Role of Lactobacillus species in the intermediate vaginal flora in early pregnancy: A retrospective cohort study. PloS ONE, 10(12). 
  3. Moreno, I., Codoñer, F. M., Vilella, F., Valbuena, D., Martinez-Blanch, J. F., Jimenez-Almazán, J., ... Simon, C. (2016, October). Evidence that the endometrial microbiota has an effect on implantation success or failure. American Journal of Obstetrics and Gynecology, 215(6), 
  4. Ravel, J., Gajer, P., Abdo, Z., Schneider, G. M., Koenig, S. S., McCulle, S. L., Karlebach, S., Gorle, R., Russell, J., Tacket, C. O., Brotman, R. M., Davis, C. C., Ault, K., Peralta, L., & Forney, L. J. (2011, March). Vaginal microbiome of reproductive-age women. Proceedings of the National Academy of Sciences of the United States of America, 108(Suppl 1), 4680–4687.
  5. Borges S., Silva J., & Teixeira, P. (2014, March). The role of lactobacilli and probiotics in maintaining vaginal health. Archives of Gynecology and Obstetrics, 289(3), 479–489. 
  6. Fettweis, J.M., Serrano, M.G., & Brooks, J.P.  (2019, May). The vaginal microbiome and preterm birth. Nature Medicine, 25, 1012–1021. 
  7. Zhang, F., Zhang, T., Ma, Y., Huang, Z., He, Y., Pan, H., Fang, M., & Ding, H. (2019, March). Alteration of vaginal microbiota in patients with unexplained recurrent miscarriage. Experimental and Therapeutic Medicine, 17(5), 3307–3316. 
  8. Wee, B. A., Thomas, M., Sweeney, E. L., Frentiu, F. D., Samios, M., Ravel, J., Gajer, P., Myers, G., Timms, P., Allan, J. A., & Huston, W. M. (2018, June). A retrospective pilot study to determine whether the reproductive tract microbiota differs between women with a history of infertility and fertile women. The Australian & New Zealand Journal of Obstetrics & Gynaecology, 58(3), 341–348.     
  9. Husain, S., Allotey, J., Drymoussi, Z., Wilks, M., Fernandez‐Felix, B.M., Whiley, A. ...Millar, M. (2019, April). Effects of oral probiotic supplements on vaginal microbiota during pregnancy: A randomised, double‐blind, placebo‐controlled trial with microbiome analysis. BJOG: An International Journal of Obstetrics and Gynaecology, 127(2), 285-286.
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