Researchers at Massachusetts Institute of Technology (MIT) have found that a simple test of cervical mucus may reveal pregnant women's risk of going into labour too early.
Up to 18 percent of babies born worldwide arrive before they are full-term, defined as 37 weeks of gestation.
The study, published in the journal Scientific Reports, showed that cervical mucus from women who delivered their babies before 37 weeks was very different from that of women who delivered later.
This type of analysis could offer an easy way to calculate the risk of early labor, potentially allowing doctors to try to intervene earlier to prevent preterm births.
"Our prediction is that we might be able to identify risk for preterm birth ahead of time, before labour sets in," said senior author of the study Katharina Ribbeck, Associate Professor at MIT.
Between 25 and 40 percent of early births are believed to be caused by infections that occur when microbes reach the uterus through the cervical plug, which is made of mucus and normally blocks access to the uterus.
For the new study, the researchers decided to investigate the mucus's permeability to small particles.
Mucus is formed from polymers known as mucins, and the composition and arrangement of these mucins determine how porous the gel is.
The researchers collected samples from two groups of patients. The low-risk group included pregnant women who came in to their doctors' offices for routine visits around 30 weeks and ended up giving birth after 37 weeks.
The high-risk group included women who went into labor early, between 24 and 34 weeks.
Doctors were able to halt labour in these women, and the samples were taken after they were stabilised. They all ended up giving birth before 37 weeks.
The researchers found a significant differences in mucus permeability and adhesiveness - the peptides were able to pass through samples from high-risk women much more easily.
This suggests that cervical mucus from women at high risk for early labour, for reasons not yet known, may be more susceptible to invasion by potentially harmful bacteria and microbes, making it more likely that those women will experience an infection that leads to preterm birth, Ribbeck said.
In addition, the altered mucus may be less able to retain helpful immune system components such as antibodies or antimicrobial peptides, which would normally help to combat infection, the study said.
Ribbeck anticipates that cervical mucus testing could be done early in pregnancy, as part of a routine screen that would reveal whether a woman was at high risk of preterm birth.