WASHINGTON (AP) -- Scientists might have found a new way to tell who's at risk of having a premature baby, by checking the bacterial community that lives in mom's reproductive tract.
Trillions of microbes share our bodies, living on the skin or in the gut, mouth or vagina, what scientists call our microbiome. Many of these germs play critical roles in health, from good digestion to robust immunity, but they can contribute to health problems if they get out of whack.
What about during pregnancy? Researchers at Stanford University tracked some of those microbial neighborhoods week by week through 49 healthy women's pregnancies - and found those who went into preterm labor harbored a different pattern of vaginal bacteria than the other moms-to-be.
It's not clear why, but there's one clue in Monday's study: At-risk mothers had low levels of lactobacillus bacteria, a family of bugs long thought important for vaginal health.
"We may have a new hook, a new angle to pursue" against preterm birth, said Dr. David Relman, a Stanford microbiology specialist who led the work. "It's possible that your microbiome could contribute to this pretty common and devastating condition."
Larger studies are needed, in diverse populations of women, to confirm the link. Another question is whether the problem is the lack of presumably protective bugs or whatever bacteria moved in in their place, noted Dr. Catherine Spong, a maternal-fetal medicine specialist at the National Institute of Child Health and Human Development.
But the finding "is very compelling," Spong said. It fits with some earlier evidence that "what our normal host flora is might be important in whether or not you're at risk for certain conditions."
If the research pans out, it raises the possibility of one day trying probiotics or other methods to alter microbial neighborhoods in women deemed at risk, said March of Dimes senior vice president Dr. Joe Leigh Simpson.
The work, published in Proceedings of the National Academy of Sciences, was partly funded by the March of Dimes Prematurity Research Center at Stanford.
About 450,000 U.S. babies are born premature, before completion of the 37th week of pregnancy. That's 11.4 percent of the babies born in 2013, a rate that has been inching down from a peak of 12.8 percent in 2006. Doctors have made strides in saving increasingly early preemies, but those babies are at greater risk of lasting vision and developmental problems.
Numerous factors play a role in preterm birth. Risks include pregnancy before age 17 or after 40, having twins or more, and the mother's own health, such as being underweight or overweight, having diabetes or high blood pressure, and whether she smokes. Part of the recent improvement in U.S. preterm birth rates came from reducing elective deliveries ahead of mom's due date, leading to a drop in "late preemies," or babies born a few weeks early.
But those factors don't explain all premature births, and scientists are trying to uncover other triggers and how to prevent them.
Alterations in people's normal microbiomes already are thought to play a role in other health conditions, from obesity to bowel disorders. And some previous research had reported that the vaginal microbiome changes when a woman becomes pregnant.
At Stanford, Relman's team took a closer look at 49 pregnant women, 15 of whom delivered prematurely. The researchers examined microbes from the vagina, stool, saliva and teeth and gums weekly during pregnancy, and monthly for up to a year afterward.
The vaginal microbiome was the one researchers linked to premature birth. In addition to low levels of lactobacilli, the women who had preemies also harbored some bacteria linked to a common condition called bacterial vaginosis.
What happened next was a surprise: Everybody harbored a different and more diverse collection of vaginal microbes after giving birth, whether they delivered early or not, vaginally or by C-section. The change lasted up to a year for some women.
The March of Dimes already recommends that women wait at least 18 to 23 months before getting pregnant again, time for the body to recover, and that finding fits, Simpson said.
"I have a feeling that the picture, the microbiome before a woman becomes pregnant or just at the time of conception may be one of the most important time points of all," said Relman, who is pursuing additional studies to try to tell.