Scientists may have discovered one of the main causes behind premature births, and it appears to have something to do with bacteria. According to an AP report, the trillions of microbes throughout a mother’s reproductive system can affect the timing of delivery to a surprising degree.

Scientists at Stanford University examined some of the vaginal microbial communities in 49 healthy pregnant women. They discovered that the women who went into early labor had a different set of vaginal bacteria than the moms who delivered on time.

Mothers at risk of giving premature birth had low levels of lactobacillus bacteria, a microbe that is widely considered important for vaginal and intestinal health. Doctors have not shown a connection between premature births and the bacteria, but the study offers a new angle to approach the issue.

Researchers speculate that a different type of bacteria may be taking the place of lactobacillus microbes. Scientists involved in the study are interested in carrying out larger trials with greater sample diversity in order to better determine the risks posed by low levels of this bacteria.

Over 10 percent of babies in the U.S. are born prematurely. Doctors have made great strides in improving the survival rate of premature babies, but these children often face serious vision and developmental risks.

The bacterial ecosystem in the reproductive system could direct the body to make certain changes over the course of a pregnancy, and with such a wide range of microbial communities identified in the initial study, subsequent research will reveal just how bacteria affect a mother’s delivery time.