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/
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