Vaginal microbiome shift in early pregnancy linked to preterm birth

Last Updated: 2017-06-08

By Anne Harding

NEW YORK (Reuters Health) - Changes in the vaginal microbiome occurring between the first and second trimester of pregnancy are associated with preterm birth, new research shows.

“There does seem to be a signal for an association between the vaginal bacterial community and preterm birth,” Dr. Molly Stout of Washington University School of Medicine in St. Louis, Missouri, told Reuters Health by phone. The study is also the first to look at the vaginal microbiome and preterm delivery in a predominately African-American cohort, she noted.

While investigators have been studying the relationship between maternal infection and preterm birth for decades, most cases of preterm birth can’t be linked to a causative microbe or microbial community, Dr. Stout and her team note in their report, online May 23 in the American Journal of Obstetrics and Gynecology.

“These data likely reflect our incomplete understanding of normal and abnormal vaginal microbial communities during pregnancy,” they add.

Recent studies have shown that the vaginal microbiome is different in pregnancy, and that there are racial differences in vaginal microbial communities, the researchers write. The one study to date of the vaginal microbiome and preterm birth included mostly white women, they add.

Dr. Stout and her team used 16S ribosomal RNA (16S rRNA) gene sequencing to characterize the vaginal microbiome in 77 women who contributed a total of 149 vaginal swabs across pregnancy. Sixty-nine percent were African-American, and 31% delivered preterm.

Community richness and Shannon diversity were stable across pregnancy in women who delivered at term. However, women who delivered preterm showed decreased vaginal microbial richness, diversity and evenness, which occurred between the first and second trimesters. Within-subject studies also linked vaginal microbiome instability with preterm birth. There were no specific bacterial taxa associated with preterm birth risk.

“The big difference that we see exists between the first and second trimester,” Dr. Stout said. “It’s not an exact specific-enough signal yet to apply clinically but we’re dialing in on it.”

The goal, she added, will be to screen women early in pregnancy and identify those who are at high risk for preterm delivery.

Understanding the mechanisms involved in the association between the vaginal microbiome and preterm birth could lead to preventive treatment, Dr. Stout said. “We can make smartly designed therapies based on these pathways we know to be abnormal to try and prevent it.”

SOURCE: http://bit.ly/2r5CUP5

Am J Obstet Gynecol 2017.