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The proportion of infants born prematurely has stayed constant at about 7 to 10 percent despite great improvements in the care of pregnant women and their babies. In half the cases of preterm birth, no cause can be identified. Researchers are finding, however, that preterm labor (PTL) may be linked to maternal infections of the vagina and genital tract. The amniotic fluid (which surrounds the fetus in the amniotic sac) of women in PTL has been tested and been found to contain infectious organisms. Also, administration of antibiotics has reduced the rate of premature birth among women with threatened (impending) PTL. But previous studies have been limited in that they typically tested for only one organism, without considering possible interactions among different organisms, and many did not correct for other risk factors for PTL. The current study investigated a range of infectious organisms and other factors thought to predispose to PTL. The subjects were 428 women in PTL, defined as labor before 37 weeks gestation, and 568 women in labor at full term (37 or more weeks gestation). Swabs were used to obtain samples of vaginal secretions, which were then tested for infectious organisms. Data analysis showed that two specific groups of bacteria were significantly associated with PTL. These groups were enteropharyngeal organisms (Escherichia coli, Klebsiella species, Haemophilus species, and Staphylococcus aureus), and the bacterial vaginosis group (normal found populating the vagina) (Gardnerella vaginalis and Bacteroides species). For each of these organisms, the percentage of women who had the organism present was higher for the preterm labor group than the full-term labor group, and the rates of infection were especially high for women in labor before 34 weeks gestation. Infections with some of these organisms produce no symptoms, while colonization with other bacteria leads to inflammation and other effects. More research is needed into sexual practices that may introduce these bacteria into the vagina and predispose to preterm labor. (Consumer Summary produced by Reliance Medical Information, Inc.)