A premature baby lies inside an incubator at an Egyptian public hospital in the province of Sharkia, northeast of Cairo, June 10, 2008. REUTERS/Nasser Nuri

WASHINGTON (Reuters) - Undiagnosed infections may be causing a significant number of premature births, researchers reported on Monday after finding bacteria or fungi in 15 percent of the amniotic fluid samples taken from women in pre-term labor.

The heavier the infection, the more likely the women were to deliver younger, sicker infants, the team at Stanford University in California found.

“If we could prevent these infections in the first place, or detect them sooner, we might one day be able to prevent some of these premature births,” Dr. Dan DiGiulio, who worked on the study, said in a statement.

More and more children are being born prematurely in the United States, with 12 percent of births coming before the 37th week of gestation. Premature babies are vulnerable to breathing problems, underdeveloped organs, infections and cerebral palsy.

DiGiulio’s team looked for the DNA of germs in amniotic fluid samples collected from 166 women in pre-term labor at the Detroit Medical Center between October 1998 and December 2002.

They used this method and standard laboratory cultures to determine that 25 of the 166 samples were infected with either bacteria or fungi. They also found at least one unknown organism that could be a new species.

All 25 of the women with infected amniotic fluid went on to deliver their babies pre-term, while 53 of the women with no infections were able to stop their labor.

Now the team is working to see if infections can be detected before pre-term labor starts, which could lead to new prevention or treatment approaches.