What if a simple blood test could predict if you were going to go into labor or go full term? A team of scientists have figured out how to do just that, and their blood test has accuracy ratings between 75 and 80%.

The breakthrough, published this month in the journal Science, is important as it may help doctors accurately predict delivery dates, but also because it’s a first step in understanding how our bodies are having conversations with our babies at a molecular level.

The study examined biomarkers in blood known as cell-free RNA, specifically cell-free RNA expressed from the placenta or fetus and found in the mother’s blood. These so called “messenger molecules” carry genetic instructions to around in our bodies.

“Because this RNA ‘floats’ around in the maternal blood, we can then detect—systemically in the mother—what might be happening to the pregnancy,” explains Michal Elovitz, a professor of obstetrics and gynecology and maternal-fetal physician at the Hospital of the University of Pennsylvania.

Elovitz contributed data to the research and conducted a scientific review of the paper. “This study—understanding that more work and validation are needed—suggests that whatever is marking the clock of gestation for term delivery is not the same for women who ultimately have a spontaneous preterm birth,” she explains.

The blood test is cheaper than an ultrasound test (but just as accurate) and a lot more accurate than the other method often used for predicting due date: Counting from the date of mom’s last period.

“We found that a handful of genes are very highly predictive of which women are at risk for preterm delivery,” says Mads Melbye, one of the study’s authors. Understanding which moms are at risk could help doctors and midwives plan in advance, and do things like move a mother to an area where she will have immediate access to care when she goes into labor. It’s important because preterm babies really need all the help they can get.

According to the CDC, preterm birth is among the leading causes of infant mortality in the U.S. And the World Health Organization estimates 15 million babies are born too soon every year. Whatever science can do to reduce poor outcomes for those preemies is welcome, say those behind the study.

“I’ve spent a lot of time over the years working to understand preterm delivery. This is the first real, significant scientific progress on this problem in a long time,” says Melbye.

Dr. Edith Cheng, a professor of maternal-fetal medicine and medical genetics at the University of Washington, tells the New York Times she sees a lot of potential in the study, beyond just the obvious ways it could help preemies. She believes further research will build on this study and show how those fetal bits that enter our blood impact our bodies and our pregnancies. “I bet you they’re going to find that the mother’s going to respond. There’s a conversation going on. That’s what’s cool,” says Cheng.

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