A new study from MIT offers hope for preventing premature birth, identifying a novel approach to evaluate the risk of early labor. Currently there is no reliable way to predict whether a woman with a normal pregnancy will go into labor before 37 weeks’ gestation, which is considered full-term.

But now, researchers have found the cervical mucus of women who deliver a baby before 37 weeks is very different from that of women who deliver later, potentially giving physicians a diagnostic tool to screen for and mitigate the risk of early labor.

Worldwide, as many as 18 percent of babies born are premies; about 1 million of them do not survive, and those who do can face developmental problems such as impaired vision or hearing, defects in the heart or lungs, or cognitive impairments.

While the causes of premature birth vary, between 25 and 40% of early births are believed to be caused by infections that occur when microbes reach the uterus through the cervical plug — that is, mucus that blocks access to the uterus during pregnancy. The study was led by Katharina Ribbeck, an associate professor of biological engineering at MIT, whose lab investigates the role of mucus in preventing infection.

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In a study published in 2013, Ribbeck found that cervical mucus from pregnant women at high risk of early labor was mechanically weaker and more elastic than that of low-risk pregnant women. For the new study, she and her colleagues decided to investigate the mucus’s permeability to small particles, such as bacteria. (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 labor in these women, and the samples were taken after they were stabilized. They all ended up giving birth before 37 weeks.

From samples collected from two groups of pregnant women — one low-risk for preterm birth, who ultimately delivered after 37 weeks, and the other high-risk, who ultimately delivered a premature baby — the researchers tested the ability of negatively charged spheres about 1 micron in diameter to travel through the mucus, and found a small but statistically insignificant difference the two groups. They then decided to do the same test with charged peptide probes (which are small enough to avoid getting stuck in the mucus network but are sensitive to the biochemical modifications of the mucus) and found a significant differences in the mucus’s ability to prevent infiltration: 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 labor, 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 says. 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.

“Mucins display all sorts of immunologically active factors that you may also lose when the adhesive properties change,” Ribbeck says.

Ribbeck anticipates that cervical mucus testing could be done early in pregnancy, as part of a routine screening for signs of potential preterm labor. (This test would determine risk from infection, but not from other potential causes of early labor.)

The next step, Ribbeck says, is to develop new ways to restore the normal function of the mucus.

The study published in the journal Scientific Reports.