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updated 1/13/2009 2:58:13 PM ET 2009-01-13T19:58:13

Previously undiscovered bacteria usually found in the mouth could be responsible for up to 80 percent of early preterm labors, estimate doctors from Case Western Reserve and Yale Universities in a new study published recently in the Journal of Clinical Microbiology.

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The research could help doctors prevent preterm births by encouraging oral hygiene or stop early labor from developing by prescribing targeted antibiotics.

"The earlier the woman goes into preterm labor, the higher the chance that she will be infected," said Yiping Han, a doctor at Case Western University and the first author on the study.

Most human pregnancies last about 40 weeks. A birth prior to 37 weeks is classified as preterm. About 12 percent of all births in the United States are preterm, a number that has grown by more than 30 percent since 1981 for reasons unknown. Babies born preterm can face many hurdles: vision and hearing loss, cerebral palsy, mental retardation, even death.

Labor itself is still somewhat of a mystery to science, which makes puzzling out preterm labor even more difficult. Anything from socioeconomic status and race to bacterial infection and genetics have been linked to preterm births, but a definitive cause is still elusive.

Strong correlation
Han and her colleagues think they have found a major cause, at least in mice. By infecting the rodents with Bergeyella, a previously unknown bacteria found in the mice, the researchers caused preterm births.

In humans, the scientists showed a strong correlation between infection and preterm births. Doctors removed amniotic fluid from 46 different women with potentially higher risk pregnancies. Of that group, 21 delivered an early preterm baby (32 weeks or earlier). Nineteen of those women, or about 85 percent, were positive for previously undetected bacteria.

The bacteria normally live in the mouth, but if a cut, cavity or other wound allows the bacteria to enter the blood stream, they can travel and eventually colonize the uterus. That triggers an immune response, which can inflame the uterus and eventually cause a mother to go into labor prematurely.

To identify bacteria behind preterm labor, doctors used polymerase chain reaction (PCR), a much more sensitive technique for finding and identifying bacteria than bacterial culturing, the current standard technique. Using PCR, the scientists identified the Bergeyella bacterium, as well as DNA belonging to 10 or 11 different strains of newly identified bacteria.

Now that doctors know about another link to preterm labor, the next step is to treat it. Antibiotics that specifically target these new bacteria are currently being tested.

"I thought it was a very interesting paper, and it seemed very sound," said Floyd Dewhirst, who is leading an effort to catalog the estimated 1,500 species of bacteria found in the human mouth at the Forsyth Institute in Boston.

"My recommendation is for women to keep their mouth as healthy as possible, and if they have periodontal disease, to get it treated before they become pregnant," said Dewhirst.

© 2012 Discovery Channel

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