Microbes might play a role in premature births

Microbes in the wrong place at the wrong time -- a woman's amniotic fluid during pregnancy -- might play a role in causing premature births, according to a study published in the online journal PLoS ONE.

Using a sensitive molecular technique, researchers found a greater quantity and variety of bacteria and fungi in a significant portion of women who gave birth prematurely. The more severe the infection, the earlier the women were likely to give birth.

The amniotic sac, which surrounds a fetus in the womb, has long been considered a protected, almost sacrosanct, site.

"Certain kinds of organisms have been known to get in and not necessarily cause any harm," said Dr. David Relman, an infectious disease specialist at Stanford University School of Medicine and the study's senior author. "But in general, bugs don't belong there."

One in eight American infants is born before full term, which is defined as 38 weeks. The high rate is attributed in part to assisted reproduction, which often results in twins or triplets. But the cause of about half of all spontaneous premature births is a mystery.

Babies born too early can have learning disabilities, neurological problems, lung diseases and cerebral palsy. Prematurity is the leading cause of infant mortality in the United States, accounting for more than one-third of all infant deaths, according to the national Centers for Disease Control and Prevention.

Dr. Dan DiGiulio, a research associate in Relman's laboratory, used two techniques of molecular biology to look for microbes in amniotic fluid samples from 166 women in preterm labor. Of these, 113 went on to deliver prematurely and 53 carried their babies full term.

DiGiulio found evidence of infection in 15 percent of the samples, all from women who gave birth early.

The microbes found represented one fungal and 17 bacterial species, including one that had never been identified, according to the report published last week.

One of the most common was Leptotrichia, which can be found in the mouth and the vagina. Both gum disease and bacterial vaginosis have been shown to increase the risks of premature delivery.