The placenta, long thought to be sterile, is home to a bacterial community similar to the one found in the mouth, researchers report today. The microbes are generally non-pathogenic, but according to the authors of the study, variations in their composition could be at the root of common but poorly understood pregnancy disorders such as preterm birth, which occurs in one out of every ten pregnancies. “This is the first study to show that even in normal pregnancy there is a specific microbiome associated with normal placentation,” says Dr. George Saade, an obstetrician at UTMB, who was not involved in the work.