"In the case of the preterm prediction, "[it's] mostly maternal genes" producing the relevant RNA, rather than the placenta-based transcripts from the due-date predictor, says Stanford University graduate student Mira Moufarrej, a lead author of the study, in a press release.
He said the findings affirmed the existence of a "transcriptomic clock of pregnancy" that could serve as a new way to access the gestational age of a foetus.
In a related study with 38 women with elevated risk of delivering preterm, researchers found seven nucleic acids that accurately identified women who went into labor up to two months early. "[It] will be important to investigate the performance of the blood test in a broader, unselected population", they write in their study.
Preterm births is the largest cause of infant mortality in the United States.
And 15 million babies a year are born prematurely worldwide.
Next, the scientists used a version of the model to see if they could predict a woman's risk of preterm delivery.
But, with a more precise delivery date, doctors could prepare earlier pregnancies that are at risk.
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Stephen Quake, a professor of bioengineering at Stanford, is a senior author on the paper, hopes that the blood test will give women "a safer and more comfortable pregnancy, both physically and psychologically".
David K. Stevenson, M.D., the principal investigator of the March of Dimes Prematurity Research Center at Stanford University, described the noninvasive blood test approach as a way of "eavesdropping on a conversation" between the mother, the fetus and the placenta, without disturbing the pregnancy.
"RNA is what's happening in the cells at any given moment", said Dr. Quake, co-president of the Chan Zuckerberg Biohub, which funded the study along with others. The estimates of gestational age given by the model were accurate about 45 percent of the time, which is comparable to 48 percent accuracy for first-trimester ultrasound estimates.
To date, doctors have no reliable way to predict if a pregnancy will result in premature birth.
The researchers used blood samples from 31 women to create a model that allowed them to estimate the fetus' age based on nine free-floating RNAs, according to The Guardian. "It tells us a lot about human development in normal pregnancy", she said.
When will a pregnant woman actually deliver her baby?
When a woman gives birth prematurely - deemed to be before 37 weeks - a number of potential complications can arise for the baby, ranging from physical development issues to behavioural and neurological disorders.
"RNA corresponding to placental genes may provide an accurate estimate of fetal development and gestational age throughout pregnancy", the report found. A study by the University of Pennsylvania linked such births to changes in the mother's bacteria. "I bet you they're going to find that the mother's going to respond".