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Bacterial community in pregnant women linked to preterm birth (2015-11-04)

A specific pattern of high bacterial diversity in the vagina during pregnancy increases a woman’s risk of giving birth prematurely, according to a study from the Stanford University School of Medicine that tracked women's microbial communities on a week-by-week basis during pregnancy.

A high-diversity pattern in the vaginal bacteria raised the likelihood of premature birth, and the longer the bacteria followed this pattern, the higher the risk, the study found. The study may also help explain why prematurity risk is elevated in women who have closely spaced pregnancies.

When the research began, little was known about whether or how the body’s indigenous communities of bacteria change in pregnancy, said the study’s senior author, David Relman, MD, professor of medicine and of microbiology and immunology at Stanford, and chief of infectious diseases at the Veterans Affairs Palo Alto Health Care System, who is also a project leader at the March of Dimes Prematurity Research Center at Stanford. “It seemed like a big missing piece of the story.”

Relman’s team studied 49 pregnant women, 15 of whom delivered prematurely. The women gave weekly samples during pregnancy, and monthly samples for up to a year after delivery, that allowed researchers to characterize the bacterial communities in the vagina, lower gut, saliva and tooth and gum areas.

The scientists found that vaginal microbial communities fell into five patterns, consistent with prior research.
For most women, the communities in the vagina and at the three other body sites did not change much during the course of pregnancy. “It’s a bit surprising how stable the communities are, since there are lots of other body features that change dramatically in pregnancy, such as maternal hormone levels, metabolism and weight,” said Relman, who holds the Thomas C. and Joan M. Merigan Professorship.

Four patterns of vaginal bacteria were characterized by little bacterial diversity and by dominance of various kinds of lactobacillus bacteria, which have been previously associated with health in women. None of these patterns were linked in the study to preterm birth.

The remaining pattern — characterized by greater bacterial diversity, high levels of gardnerella and ureaplasma bacteria, and low levels of lactobacillus — was linked with increased risk for preterm birth, especially if the bacterial community displayed this pattern for several weeks.

“It may be that an event in the first trimester or early second trimester, or even prior to pregnancy, starts the clock ticking” said the study’s lead author, Daniel DiGiulio, MD, a research associate and clinical instructor in medicine.

The researchers also found that, in all women, vaginal bacterial communities changed significantly after birth. This was true both of women who delivered prematurely and at term.
The change was seen after both vaginal and cesarean deliveries.
For up to a year after birth, women tended to have the more-diverse bacterial pattern.

Though the findings need to be confirmed in a larger, more diverse group of women, they may ultimately help doctors identify which women are at risk for premature delivery, the researchers said.
The findings also raise the possibility that treatment with probiotics or other interventions designed to alter the body’s communities of bacteria may help ward off prematurity, a concept the researchers hope to test in future studies.

“Traditionally, we viewed microbes as pathogens — as bad actors,” said DiGiulio. “We now recognize that our bodies’ microbial communities perform many beneficial functions, yet there may be times when the communities get out of whack.”

Other Stanford-affiliated co-authors of the study are research associates Benjamin Callahan, PhD, Elizabeth Costello, PhD, and Paul McMurdie, PhD; Deirdre Lyell, MD, associate professor of obstetrics and gynecology; Anna Robaczewska, MS, research assistant; postdoctoral scholars Christine Sun, PhD, and Daniela Goltsman, PhD; Ronald Wong, PhD, senior research scientist; Gary Shaw, DrPH, professor of pediatrics; and Susan Holmes, PhD, professor of statistics. Lyell, Shaw and Stevenson are members of Stanford’s Child Health Research Institute.

For more information
PNAS
Temporal and spatial variation of the human microbiota during pregnancy
Link...

Stanford University School of Medicine
https://med.stanford.edu/

MDN