The researchers identified a comprehensive list of microbial species in intra-amniotic infections by using new DNA methods to track down the presence of bacteria, the researchers said.

To increase their accuracy the investigators used a combination of analyses including proteomics results of amniotic fluid and histological analysis of the placenta to corroborate the infection and inflammation.

Intra-amniotic inflammation is known to set off spontaneous births of preterm babies at less than 32 weeks, said lead investigator Yiping Han of Case Western Reserve University said.

The study involved 46 women of which 44 experienced preterm births.

The study, published in the Journal of Clinical Microbiology, found bacteria levels from the amniotic fluids of pregnant women with signs or symptoms of preterm births were compared to those of a control group of 16 women without such manifestations and who delivered at term.

These bacteria reach the placenta through the genital tract or through the blood to the placenta. Han suspects some originate in the mouth which has hundreds of dozens of bacteria present.