NEW YORK (Reuters Health) - Certain bacteria may make their way from the mouth to the amniotic fluid, possibly putting pregnant women at risk of miscarriage, preterm delivery and other complications, according to the results of a preliminary study.

The amniotic fluid that surrounds the developing fetus is normally sterile. Infection within the amniotic sac, as a result of spread from the genital tract or medical procedures such as amniocentesis, can increase the risk of premature labor. One theory is that bacteria found in the mouth might also reach the amniotic fluid via the bloodstream, especially in women with inflamed or diseased gums.

In the study, the investigators analyzed samples of dental plaque and amniotic fluid from 48 women attending a hospital for an elective cesarean section. The average age of the study volunteers was 31 years.

The researchers found the DNA of a type of bacteria commonly found in the mouth in 7 out of 48 samples tested, according to the report in a recent issue of the British Journal of Obstetrics and Gynaecology. However, they were unable to culture, or grow the bacteria in the laboratory, suggesting that although DNA was present, the bacteria were present at very low levels or were not capable of causing infection.

The researchers did find, however, an association between microbes--both mouth bacteria and other types--in the amniotic fluid and complications in the women's previous pregnancies, including miscarriage, preterm delivery, premature rupture of the amniotic sac and death of the newborn.

"It is well recognized that DNA can persist in tissues for some time and may well have remained from a previous pregnancy," write Dr. Caroline Bearfield and colleagues from Queen Mary's School of Medicine and Dentistry, University of London, UK.

More study is needed to confirm the findings.

The researchers note that they used an extremely sensitive technique called PCR to check for genetic material from microbes in the various samples. Therefore, they add, the role of infection in pregnancy complications may have been underestimated by previous research using less sensitive tests.

SOURCE: British Journal of Obstetrics and Gynaecology 2002;109:527-533.

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