Bacteria in Cervix, Vagina May Influence Risk of Spontaneous Preterm Birth

By Rob Goodier

February 06, 2017

NEW YORK (Reuters Health) - Researchers have identified bacterial species in the cervix and vagina that may be linked to the risk of spontaneous preterm birth.

"It is very exciting data and hopefully will lead us on a new path to identifying women at risk for preterm birth but also finding new cures to prevent prematurity," Dr. Michal Elovitz of the University of Pennsylvania in Philadelphia told Reuters Health by email.

Dr. Elovitz and colleagues, who presented their findings January 26 at the Society for Maternal-Fetal Medicine's annual conference in Las Vegas, Nevada, sought to assess differences in cervicovaginal microbial populations between women who suffer preterm birth and those who carry to term.

"Although conventional wisdom says premature birth begins in the uterus, we decided to take an entirely new look at the problem," Dr. Elovitz explained in a statement.

The study included 2,000 women pregnant with singletons, with samples taken three times from weeks 16 to 28. The researchers identified 83 cases of preterm birth and compared their data with those of 336 matched controls who delivered at term.

To validate the findings, the team added a second, separate cohort of 616 women with specimens collected between 22 and 32 weeks.

At least 37 bacterial species were associated with significant protection against spontaneous preterm birth. Bifidobacteria in particular were the most consistently protective across gestational time points and by race, Dr. Elovitz said.

On the other side of the spectrum, 13 bacterial species were linked to an uptick in preterm birth - most dramatically bacterial vaginosis-associated bacterium 2 (BVAB2), BVAB3 and Mobiluncus.

Racial differences also emerged in these associations. Frequency matching by race revealed that certain (but not all) of the bacteria identified appeared to affect the length of the term only in white people, while others affect only black people.

"In other words, race matters in regards to the risk from the bacteria and preterm birth," Dr. Elovitz said.

An explanation for the findings may have something to do with immune responses.

"We believe that either by losing 'good' bugs, or by having too many 'bad bugs,' that this results in an unfavorable immune response," Dr. Elovitz said. "This leads to changes in the surface of the cervix (the cervical epithelial barrier), which in turn leads to the cervix changing early, making it shorten and open and then preterm birth follows."

If confirmed, the findings could prompt screening and even treatment to prevent preterm birth, experts say.

"From these data, we may learn how to prevent preterm birth either by eliminating the cervicovaginal bacteria that are associated with an increased risk and/or by enhancing the presence of protective bacteria," Dr. Edward McCabe, chief medical officer of the March of Dimes, said in a statement.

"This is a promising new area that should become a research priority," he added.

The research won the March of Dimes Award for Best Abstract on Prematurity presented at the conference.


Am J Obstet Gynecol 2017.