Lately, there’s been lots of talk about your vaginal microbiome—the bacteria, viruses, and fungi that live in your vagina—and how it affects the development of your baby’s microbiome. It also turns out that the microbes living in and on your body can also affect whether your baby grows to term (usually considered at least 37 weeks gestation) or whether they’re born early, which is also called preterm or premature.
Worldwide, about 10 percent of babies are born preterm, and one known cause of preterm birth is the growth of bacteria in the amniotic fluid. In this blog post, we’ll discuss the evidence for the influence of your microbiome on your fertility and your baby’s birthday, as well as how you can best take care of your microbiome.
Researchers have made connections between the composition of the vaginal microbiome and both the success of in vitro fertilization and miscarriage. In 2019, a team of researchers in The Netherlands showed that they could predict the success of in vitro fertilization attempts based on which species of microbes were present and in what amounts in the vaginal microbiome.  A 2020 study, led by researcher David MacIntyre of Imperial College London, revealed connections between the composition of the vaginal microbiome and first-trimester miscarriage.  This finding is intriguing because it could mean that modifying the microbiome could help decrease some early miscarriages.
With regard to preterm birth, there has been lots of evidence that points to a connection between the microbes present in the vagina and when baby is born. MacIntyre’s group at Imperial College London, for instance, has shown that vaginal dysbiosis—a condition when the microbes in the vagina aren’t present in typical amounts or ratios—is connected to premature rupture of membranes, which is when your bag of waters breaks early, and consequent preterm birth. 
And in a study published in Nature Medicine in 2019, Jennifer Fettweis, a microbiologist at Virginia Commonwealth University, and her colleagues analyzed microbiome data collected as part of the Human Microbiome Project.  They found that women whose babies were born early had a different make up of microbes in their vaginal microbiomes than women whose babies were born at term. The authors suggest that microbes that were more common in women who had premature babies may have affected inflammation in the vagina.
Despite the known influence of the vaginal microbiome on fertility, miscarriage, and birth timing, it’s not particularly easy or routine to check the composition and health of someone’s vaginal microbiome. To solve this problem, MacIntyre’s group recently developed a way to quickly and simply make an educated guess about the vaginal microbiome composition from just one test—work they published in Nature Communications in October 2021.  With just one vaginal swab—a test you already do during pregnancy when you’re tested for the presence of Group B Strep—researchers can get a good idea about which microbes are present in the vagina. The authors write that if the composition of the vaginal microbiome is known, it might help clinicians decide who is most at risk for preterm birth and to monitor those people more carefully and potentially prevent babies from being born early.
If you’re curious about your microbiome and want to take good care of it during pregnancy, what can you do? First, don’t douche or use any kind of product to “clean” your vagina. It’s self-cleaning and washing your vulva (the outside of your genitals) with water in the shower is adequate. Plus, douching or using cleaning products in your vagina could disrupt your microbiome. Finally, eating well, exercising, and drinking plenty of water will help keep your whole body, including your vagina and the microbes that live there, happy.
- Koedooder, R. et al. (2019). The vaginal microbiome as a predictor for outcome of in vitro fertilization with or without intracytoplasmic sperm injection: a prospective study. Human reproduction.
- Al-Memar, M. et al. (2020). The association between vaginal bacterial composition and miscarriage: a nested case-control study. BJOG : an international journal of obstetrics and gynaecology.
- Brown, R. G. et al. (2018). Vaginal dysbiosis increases risk of preterm fetal membrane rupture, neonatal sepsis and is exacerbated by erythromycin. BMC medicine.
- Fettweis, J. M. et al. (2019). The vaginal microbiome and preterm birth. Nature medicine.
- Pruski, P. et a. (2021). Direct on-swab metabolic profiling of vaginal microbiome host interactions during pregnancy and preterm birth. Nature communications.