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Why Aren’t We Talking About How the Vaginal Microbiome Impacts Fertility?

Take a peek at how the dynamic microbial world within your vagina might influence your fertility status, preterm birth risk, and more.

5 minutes

25 Citations

If you’re trying to get pregnant, you’ve no doubt received plenty of advice (solicited or not) about how to go about it. 

Chances are, this guidance discounts a key piece of the fertility puzzle: the dynamic microbial world that populates your vagina. We reached out to Ava Mainieri, Ph.D., a geneticist and evolutionary biologist specializing in female reproductive health, to learn about how the vaginal microbiome impacts fertility, and what this means for anyone trying to get pregnant. 

“The first thing I think you should do is take a deep breath, and know that everything is going to be okay,” Dr. Mainieri says. “Women don’t hear that enough in their care.”

So with that: inhale, exhale, and let’s begin.

Let’s Get Microscopic: How Your Vaginal Ecosystem Impacts Fertility

Your vaginal microbiome (VMB) is a living landscape of billions of microscopic organisms, predominantly bacteria. Ideally, these bacterial communities work synergistically to help keep your vagina comfortable and infection-free.1,2

Unlike the gut microbiome, which is more diverse, your VMB seems to operate best when it is dominated by one certain microbial genus: Lactobacillus. Dysbiosis, characterized by a decrease in Lactobacillus species and an increase in other types of bacteria in the VMB, may contribute to inflammation and an increased risk of conditions like bacterial vaginosis (BV).3 

Dr. Mainieri explains that the VMB and lactobacilli also play an essential role during fertility and pregnancy. Once an egg is fertilized, it must be implanted into the uterine lining, and imbalances in the vaginal microbiome such as bacterial vaginosis (BV) have been associated with increased rates of implantation failure.4 How, exactly, vaginal lactobacilli modulate implantation is still up for debate. It could be that VMBs with an abundance of lactobacilli and low overall bacterial diversity help decrease inflammation in the reproductive tract and/or create an acidic environment that supports embryo implantation in the uterine cavity.5,6 

Back in 2005, scientists made the first attempt to go beyond associations and show a direct causal relationship between Lactobacillus species and implantation outcomes. To do so, they gave women undergoing IVF an intravaginal probiotic during embryo transfer. In the end, the probiotic did not have any impact on implantation rates or pregnancy outcomes.7 

However, this research was done before the scientific community knew which specific strains of Lactobacillus most often occurred in the vagina. You see, Lactobacillus is at the top of its bacterial family tree. Underneath it, there are at least 170 species, and within those species, there are countless strains—each with a unique role to play.8 We now know that some strains within the Lactobacillus crispatus species, specifically, seem to be associated with a healthy pregnancy and positive birth outcomes.9-11

A more recent study, published in 2023, found that taking a Lactobacillus probiotic decreased the chance of miscarriage but didn’t have any impact on pregnancy rates among those undergoing IVF. However, this study also used a Lactobacillus strain not commonly dominant in vaginas (Lactobacillus acidophilus)​​.12 

This goes to show how important strain-level specificity is to the study of probiotics. It’s still possible that probiotics formulated with naturally occurring vaginal Lactobacillus strains could help decrease miscarriage risk and support implantation (during IVF or natural conception), Dr. Mainieri explains—but we need more granular research to be sure.

The role of the VMB in fertility also seems to expand beyond the uterine lining. The cervix, a muscular barrier between the vagina and the uterus, is protected by a thick mucus lining that facilitates the transfer of sperm to the uterus. The exact relationship between vaginal microbes, cervical mucus, hormones, and fertility is an active area of scientific investigation—but the vaginal microbiome does indeed seem to influence the composition of the cervix.13,14 This is yet another potential way the VMB may impact fertility. 

Nine Months Later: How the VMB Impacts Birth Outcomes

Recent research from the NIH’s Human Microbiome Project (HMP) found that those who delivered preterm tended to have vaginal microbiomes lower in L. crispatus.11

This is a significant and timely finding, as premature births (before 37 completed weeks of pregnancy) are once again on the rise in the U.S. after years of decline.15,16 About 1 in 10 babies are now born prematurely in this country every year, putting them at greater risk of certain respiratory, gastrointestinal, and immune diseases.15,17

So, how might the VMB play a role in reversing this disturbing trend? It could be that vaginal environments dominated by lactobacilli are more protective against sexually transmitted infections (STIs).18 STIs might increase the risk of preterm birth by triggering an inflammatory response that can lead to cervical remodeling and premature rupture of fetal membranes.11,19 L. crispatus is also protective against vaginal microbiome disturbances like BV, which has been linked to an increased risk of preterm birth.11,20

While there appears to be a genetic component to some preterm births, nutrient-poor diets, high stress levels, and some vaginal hygiene products may also be risk factors—potentially to some degree due to their influence on the vaginal microbiome.2-24

The more we uncover about the function of the VMB, the closer we get to preventing preterm births and improving pregnancy outcomes around the world. However, research on how the vaginal microbiome impacts fertility and childbirth is still very much ongoing, and you should always work with your OB/GYN to formulate your personal care plan.

Seeding a Brighter Future

It’s important to protect your vaginal microbiome throughout your life—but especially when you’re pregnant or trying to get pregnant. We still have a lot to learn about what an “optimal” vaginal microbiome looks like (and it definitely varies from person to person), but existing research suggests that VMBs higher in certain strains like L. crispatus tend to be stronger and more resilient.18

Building a healthy VMB will serve you (and your child) long after birth. A mother’s vaginal microbiota imprints on their child via vaginal birth, skin-to-skin contact, and breastfeeding, helping set newborns up to develop strong microbiota of their own.25 This process, appropriately called “seeding,” reminds us that vaginal microbes are one of the first—and more valuable—gifts we can give our children.

Citations

  1. Reid, G. (2017). Therapeutic opportunities in the vaginal microbiome. Microbiology Spectrum, 5(3). https://doi.org/10.1128/microbiolspec.bad-0001-2016
  2. Chen, X., Lu, Y., Chen, T., & Li, R. (2021). The female vaginal microbiome in health and bacterial vaginosis. Frontiers in Cellular and Infection Microbiology, 11. https://doi.org/10.3389/fcimb.2021.631972
  3. Han, Y., Liu, Z., & Chen, T. (2021). Role of vaginal microbiota dysbiosis in gynecological diseases and the potential interventions. Frontiers in Microbiology, 12, 643422. https://doi.org/10.3389/fmicb.2021.643422
  4. Ravel, J., Moreno, I., & Simón, C. (2021). Bacterial vaginosis and its association with infertility, endometritis, and pelvic inflammatory disease. American Journal of Obstetrics and Gynecology, 224(3), 251–257. https://doi.org/10.1016/j.ajog.2020.10.019
  5. Dabee, S., Passmore, J. S., Heffron, R., & Jaspan, H. B. (2021). The Complex link between the female genital microbiota, genital infections, and inflammation. Infection and Immunity, 89(5), e00487-20. https://doi.org/10.1128/IAI.00487-20
  6. Gardner D. K. (2015). Lactate production by the mammalian blastocyst: Manipulating the microenvironment for uterine implantation and invasion?. BioEssays: News and Reviews in Molecular, Cellular and Developmental Biology, 37(4), 364–371. https://doi.org/10.1002/bies.201400155
  7. Gilboa, Y., Bar-Hava, I., Fisch, B., Ashkenazi, J., Voliovitch, I., Borkowski, T., & Orvieto, R. (2005). Does intravaginal probiotic supplementation increase the pregnancy rate in IVF-embryo transfer cycles? Reproductive Biomedicine Online, 11(1), 71–75. https://doi.org/10.1016/s1472-6483(10)61301-6
  8. Goldstein, E. J. C., Tyrrell, K. L., & Citron, D. M. (2015). Lactobacillus species: Taxonomic complexity and controversial susceptibilities. Clinical Infectious Diseases, 60(suppl_2), S98–S107. https://doi.org/10.1093/cid/civ072
  9. Starc, M., Lučovnik, M., Eržen Vrlič, P., & Jeverica, S. (2022). Protective effect of Lactobacillus crispatus against vaginal colonization with group b streptococci in the third trimester of pregnancy. Pathogens (Basel, Switzerland), 11(9), 980. https://doi.org/10.3390/pathogens11090980
  10. Gudnadottir, U., Debelius, J. W., Du, J., Hugerth, L. W., Danielsson, H., Schuppe-Koistinen, I., Fransson, E., & Brusselaers, N. (2022). The vaginal microbiome and the risk of preterm birth: A systematic review and network meta-analysis. Scientific Reports, 12(1). https://doi.org/10.1038/s41598-022-12007-9
  11. Fettweis, J. M., Serrano, M. G., Brooks, J. P., Edwards, D. J., Girerd, P. H., Parikh, H. I., Huang, B., Arodz, T. J., Edupuganti, L., Glascock, A. L., Xu, J., Jimenez, N. R., Vivadelli, S. C., Fong, S. S., Sheth, N. U., Jean, S., Lee, V., Bokhari, Y. A., Lara, A. M., . . . Buck, G. A. (2019). The vaginal microbiome and preterm birth. Nature Medicine, 25(6), 1012–1021. https://doi.org/10.1038/s41591-019-0450-2
  12. Thanaboonyawat, I., Pothisan, S., Petyim, S., & Laokirkkiat, P. (2023). Pregnancy outcomes after vaginal probiotic supplementation before frozen embryo transfer: A randomized controlled study. Scientific Reports, 13(1). https://doi.org/10.1038/s41598-023-39078-6
  13. Vagios, S., & Mitchell, C. M. (2021). Mutual preservation: A review of interactions between cervicovaginal mucus and microbiota. Frontiers in Cellular and Infection Microbiology, 11. https://doi.org/10.3389/fcimb.2021.676114
  14. Dong, M., Dong, Y., Bai, J., Li, H., Ma, X., Li, B., Wang, C., Li, H., Qi, W., Wang, Y., Fan, A., Han, C., & Xue, F. (2023). Interactions between microbiota and cervical epithelial, immune, and mucus barrier. Frontiers in Cellular and Infection Microbiology, 13. https://doi.org/10.3389/fcimb.2023.1124591
  15. Preterm birth. (2023, December 14). Maternal Infant Health. https://www.cdc.gov/maternal-infant-health/preterm-birth/?CDC_AAref_Val=https://www.cdc.gov/reproductivehealth/maternalinfanthealth/pretermbirth.htm
  16. Martin, J. A., & Osterman, M. J. K. (2024). Shifts in the distribution of births by gestational age: United States, 2014-2022. National Vital Statistics Reports: From the Centers for Disease Control and Prevention, National Center for Health Statistics, National Vital Statistics System, 73(1), 1–11.
  17. Behrman, R. E., Butler, A. S., & Institute of Medicine (US) Committee on Understanding Premature Birth and Assuring Healthy Outcomes (Eds.). (2007). Preterm Birth: Causes, Consequences, and Prevention. National Academies Press (US).
  18. France, M., Alizadeh, M., Brown, S. E., Ma, B., & Ravel, J. (2022). Towards a deeper understanding of the vaginal microbiota. Nature Microbiology, 7(3), 367–378. https://doi.org/10.1038/s41564-022-01083-2
  19. Gao, R., Liu, B., Yang, W., Wu, Y., Wang, B., Santillan, M. K., Ryckman, K., Santillan, D. A., & Bao, W. (2021). Association of maternal sexually transmitted infections with risk of preterm birth in the United States. JAMA Network Open, 4(11), e2133413. https://doi.org/10.1001/jamanetworkopen.2021.33413
  20. Ng, B. K., Chuah, J. N., Cheah, F. C., Ismail, N. a. M., Tan, G. C., Wong, K. K., & Lim, P. S. (2023). Maternal and fetal outcomes of pregnant women with bacterial vaginosis. Frontiers in Surgery, 10. https://doi.org/10.3389/fsurg.2023.1084867
  21. Couceiro, J., Matos, I., Mendes, J. J., Baptista, P. V., Fernandes, A. R., & Quintas, A. (2021). Inflammatory factors, genetic variants, and predisposition for preterm birth. Clinical Genetics, 100(4), 357–367. https://doi.org/10.1111/cge.14001
  22. Gete, D. G., Waller, M., & Mishra, G. D. (2019). Effects of maternal diets on preterm birth and low birth weight: A systematic review. British Journal of Nutrition, 123(4), 446–461. https://doi.org/10.1017/s0007114519002897
  23. Burris, H. H., Riis, V. M., Schmidt, I., Gerson, K. D., Brown, A., & Elovitz, M. A. (2020). Maternal stress, low cervicovaginal β-defensin, and spontaneous preterm birth. American Journal of Obstetrics & Gynecology, Maternal-fetal Medicine, 2(2), 100092. https://doi.org/10.1016/j.ajogmf.2020.100092
  24. Janssen, L. E., Verduin, R. J. T., De Groot, C. J. M., Oudijk, M. A., & De Boer, M. A. (2022). The association between vaginal hygiene practices and spontaneous preterm birth: A case-control study. PloS One, 17(6), e0268248. https://doi.org/10.1371/journal.pone.0268248
  25. Hourigan, S. K., & Dominguez-Bello, M. G. (2023). Microbial seeding in early life. Cell Host & Microbe, 31(3), 331–333. https://doi.org/10.1016/j.chom.2023.02.007