How Does Your Microbe Community Change During Pregnancy?


The vaginal microbiota undergoes major compositional changes throughout a women’s lifespan from birth, to puberty, to menopause. However, very little is known about the composition of the vaginal microbiota throughout these transitional stages (Romero 2014). So if the microbial community of the vagina changes throughout a women’s life, how does pregnancy change it, if it does at all?

Normal pregnancies (carried to term) represent a short but dramatic change in anatomy, physiology, and immune function. Some of the many changes a female body needs to do is develop the placenta, increase their hormone levels, and develop changes in their immune response to prevent their body from rejecting the fetus. These changes may drive alterations in the structure and composition of the microbial community which results in a changed microbiome.

The human microbiota plays a huge role in our health, yet little is known about the changing microbial make-up of the vagina during and after pregnancy (DiGiulio 2015). Establishing a baseline for the vaginal microbiome during pregnancy will be a crucial step in possibly being able to predict and prevent pregnancy complications like preterm birth and bacterial vaginosis. Past studies have shown that the vaginal microbial community has shown an increase in Lactobacillus abundance with reduced richness and diversity when compared to the vaginal microbiome of non-pregnant women (Freitas 2017).

But what about the rest of the body? Pregnancy changes the whole female body, so does that mean that the microbial community in other body sites can change as well? Even though pregnancy alters a women’s body so drastically, there haven’t been many studies looking into the changes it can cause in microbial structure throughout the whole body. Only two previous studies have simultaneously looked at body sites other than the vagina when looking at microbial community change throughout pregnancy.

Central Question

How does the microbial community within the mother’s body change throughout as well as after pregnancy?


Figure demonstrating the five different community groups observed (from figure 2 in DiGiulio 2014)

DiGiulio et al. found that the progression of pregnancy is not associated with a dramatic remodeling of the diversity and composition of a women’s microbiota, but that the vaginal community transitions between five main community types. Four of these community types were dominated by a Lactobacillus species and were more stable than a fifth diverse group. Not only did they find that the diverse group exhibited a stronger association with preterm birth, but they also found that the amount of time the vaginal community remained in this diverse state have an effect on gestation time, usually resulting in preterm birth.

When looking at the diverse group independently, DiGiulio et al. found that when Lactobacillus abundance was low there was a high abundance of Gardnerella (bacterial vaginosis) and Ureaplasma present in the vagina, which may increase the risk of preterm birth. This could be due to the Gardnerella and Ureaplasma outcompeting the Lactobacilli for resources in the vagina.

Not only did the vaginal community change between these five groups throughout the pregnancy, but it then changed again after delivery. DiGiulio et al. found that delivery, either by C-section or vaginally, was typically accompanied by a huge increase in community diversity after delivery. The Lactobacilli were replaced by other microbes that do not rely on oxygen for growth known as anaerobic bacteria. These changes resulted in the vaginal community to be more similar to the gut community and remained this way up to a year after delivery. This change in community can result in future pregnancy problems if conception occurs too soon after delivery, meaning women should give their bodies time to re-stabilize after giving birth before getting pregnant again. For example, one problem that could happen is that the new fetus is unable to survive in the altered community, resulting in the mother having a miscarriage.

Furthermore, DiGiulio et al. did not find any significant and dramatic changes in microbial community in the three other body sites that were swabbed (gut, saliva, tooth/gum) during the course of the pregnancy.

My Questions

Many studies have found that the vaginal community of pregnant women is dominated by Lactobacillus species and is described to have lower richness and diversity than non-pregnant women. Below in the further reading section, the What is Vaginal Microbiome? article states that the dominance of Lactobacilli appears to be unique to humans, so why do Lactobacillus species only dominate the human vaginal community and not other animal species? One possible answer to this could be that they outcompete the other present species for the limited resources to survive.

Both Gardnerella and Ureaplasma have been implicated as having potential roles in pregnancy complications with preterm birth when paired with low Lactobacillus abundance. Why do these two pathogens cause complications? Do they only cause complications when there is a low abundance of Lactobacillus? Is there any treatments that can help stabilize the low Lactobacillus abundance or that can fight off Gardnerella or Ureaplasma? Looking more into Gardnerella and Ureaplasma would be a good next step in preventing pregnancy problems.

Further Reading

To compare the findings of this study to the vaginal microbial community throughout a non-pregnant women’s lifetime, Larry Forney from the University of Idaho looked at the Causes and consequences of temporal changes in the vaginal microbiome. Forney looked at the vaginal microbiome in about 350 women from four different ethnic groups and found that the vaginal community dynamics are highly personalized to the individual women. Forney also talks about the five different community groups he found and discusses the changes of pH in the vagina.

For more information on the vaginal microbiome in healthy women, the article What is Vaginal Microbiome? talks about Lactobacilli and their function in the vagina. There is also a video in the article, and in the first four minutes Jacques Ravel goes a little more in depth about the changes the vaginal microbial community makes throughout a women’s lifetime. Ravel discusses that the vagina is actually sterile at birth but is then quickly colonized by Lactobacilli, but after 3-4 weeks the Lactobacilli disappear until puberty, he then goes on to discuss one of his studies on the vaginal microbiome. The article also talks about the possible positive effects probiotics can have on vaginal communities.


  • DiGiulio, D. B., Callahan, B. J., McMurdie, P. J., Costello, E. K., Lyell, D. J., Robaczewska, A., … & Stevenson, D. K. (2015). Temporal and spatial variation of the human microbiota during pregnancy. Proceedings of the National Academy of Sciences, 112(35), 11060-11065. doi:  10.1073/pnas.1502875112
  • Forney, Larry. “Causes and Consequences of Temporal Changes in the Vaginal Microbiome.’ Institute of Arctic Biology::Life Science Hour Seminars, 1 Mar. 2018,
  • Freitas, A. C., Chaban, B., Bocking, A., Rocco, M., Yang, S., Hill, J. E., & Money, D. M. (2017). The vaginal microbiome of pregnant women is less rich and diverse, with lower prevalence of Mollicutes, compared to non-pregnant women. Scientific Reports, 7(1), 9212. doi:  10.1038/s41598-017-07790-9
  • MeÅ¡trović, Tomislav. “What Is Vaginal Microbiome?’, AZoNetwork, © 2000-2018, 23 Aug. 2018,
  • Romero, R., Hassan, S. S., Gajer, P., Tarca, A. L., Fadrosh, D. W., Nikita, L., … & Chaiworapongsa, T. (2014). The composition and stability of the vaginal microbiota of normal pregnant women is different from that of non-pregnant women. Microbiome, 2(1), 4. doi:  10.1186/2049-2618-2-4