Vaginal bacteria linked to premature birth

By Dr. Liji Thomas, MDApr 8 2020

A new study published in the journal Frontiers in Microbiology in April 2020 reports that women who deliver early are more likely to have a greater variety of bacteria in their birth canals. The research also highlights specific bacteria that are associated with premature birth. This knowledge could help design tests to screen for high-risk pregnancies.

Preterm birth, defined as being born before 37 completed weeks of pregnancy, affects 15 million babies, according to 2012 statistics released by the World Health Organization (WHO). Preterm birth is often a complicated issue. The babies are not fully competent to live outside the mother's womb, leading to multiple medical problems, delayed neurodevelopmental outcomes, and infant death. Indeed, preterm birth is the most common cause of death in newborns.

The risk factors for preterm birth include a high maternal age, increased maternal stress, and maternal malnutrition, among others, but the mechanism through which these operate to advance the date of labor is less clear. Not knowing why the woman goes into labor limits the ability to intervene effectively, as researcher Marina Sirota explains, "new ways of identifying women at higher risk is sorely needed."

Scientists have been trying to pick out areas that contribute to premature labor. One such area of research is the role of various microbes in the vaginal microbiome. However, most such studies have been carried out on a small scale and include only one ethnic group. This limits their generalizability to other populations.

3d illustration - Lactobacillus Bulgaricus Bacteria / Shutterstock.com

The current study

The researchers tried to overcome this difficulty by carrying out a meta-analysis. This type of study brings together data from multiple studies into a single large dataset, explains co-researcher Idit Kosti. The findings yield more information while expanding the range of composition of the population, to make it more inclusive in terms of ethnic origin and stage of gestation. As a result, the resulting analysis is more generalizable than each individual study.

The investigators brought together five datasets, with over 3,000 samples of the vaginal microbiome from 400-plus women. This helped them identify previously unknown links between the vaginal microflora, certain specific bacteria, and the risk of preterm delivery.

The findings

Kosti says, "We found that women who deliver prematurely have a significantly more diverse vaginal microbiome, especially in their first trimester, than those who deliver at full term. In addition to confirming several bacterial species known to be associated with premature birth, we have identified several new ones."

In addition, they report that specific microbes are more often found in women who deliver early. Some bacterial species, like Lactobacillus, have already been the subject of older studies, and are known to be found more commonly in women who deliver at full term. On the other hand, some species like Olsenella and Clostridium sensu stricto have been identified in this study for the first time to herald an early delivery.

What does this information mean?

Hopefully, this information will help discover new testing methods to identify pregnant women who are at high risk for preterm labor. The research methods can be used by other investigators to combine still more studies on this theme. This could help screen mothers as well as develop treatments to avert this condition, which is costly in terms of human life, suffering, and financial expenditure.

Earlier studies have, however, shown that different ethnic and racial groups have distinctive microbiomes. High bacterial diversity, along with the presence of bacteria like Gardnerella vaginalis, Atopobium vaginae, and Veillonellaceae that are associated with bacterial vaginosis, were found to predict early spontaneous preterm birth, in another study. This could mean that a one-size-fits-all approach to vaginal microbiome screening might not work well to screen pregnant women at risk. More work needs to be done to define a 'normal' pregnant microbiome in the vagina.