Scientists have found a higher number of pathogenic bacteria in placentas from women who delivered prematurely, supporting the presumption that maternal infection may cause preterm birth -- less than 37 weeks gestation.

Contradicting general belief, traces of the bacteria were found in healthy placentas as well. These bacteria have been previously reported as opportunistic intra-uterine -- within the uterus -- pathogens, and are highly correlated with the incidence of premature birth and miscarriage. "We did observe a higher number of known pathogenic bacteria, such as Mycoplasma and Ureaplasma, in the placenta of women who had a preterm spontaneous birth which supports the long-observed association between maternal infection and preterm birth," said Lydia J. Leon from the University College London, Britain.

For the study, published in the journal Applied and Environmental Microbiology, the team investigated bacteria in both healthy and preterm placental samples from more than 250 women. "There was a clear difference in the types of bacteria observed in a placenta, dependent on whether (the baby) was delivered by caesarean section or vaginally," said Leon. However, much of those differences may reflect contamination picked up during delivery rather than bacteria present in the placenta prior to delivery, according to the report.

"Our understanding of spontaneous preterm birth is relatively limited. That was the motivation for the research," Leon added. Preterm birth is linked with both psychological and physical disabilities and is considered as the leading cause of infant morbidity and mortality worldwide. Infection is known to be an important cause of spontaneous preterm birth. "If we better understand the involvement of bacteria during pregnancy, we can develop more targeted treatment to hopefully prevent preterm birth and save lives," Leon said.