Additionally, the researchers observed differences between the placental microbiome of infants born slightly prematurely and infants born at full term, suggesting a link between bacterial composition in the placenta and preterm birth.

"Exposure of the fetus to a placental microbiome may have fundamental implications for early human development and the physiology of pregnancy," said James Versalovic, co-author of the report and professor of pathology at Baylor and head of pathology at Texas Children's Hospital.

They plan to further explore the connection in a future study looking at the oral and placental microbiomes of more than 500 women at risk for preterm birth.

The knowledge could "lead to rapid breakthroughs in not only identifying women at risk for preterm birth, but developing new and worthwhile strategies to prevent preterm birth," said Aagaard.