But ultrasound can be expensive or unavailable. "With further study, we might be able to identify specific genes and gene pathways that could reveal some of the underlying causes of preterm birth, and suggest potential targets for interventions to prevent it".
Recent research from the U.S. has shown that the number of premature births climbed to 9.93pc in 2017, up from 9.86 in 2016, making it the third consecutive annual increase after steady declines over the previous seven years.
In the past, doctors have lacked a way to predict which pregnancies will end more than three weeks before the mother's due date.
And it is hard to accurately predict delivery dates, she said.
Stevenson, M.D., principal investigator at the March of Dimes Prematurity Research Center at Stanford University, describes the PCR-based tests, which can be carried out on a single blood sample, as effectively "eavesdropping on a conversation" among the mother, the fetus, and the placenta.
Researchers have developed an affordable blood test they say can predict a pregnant women's due date and potentially identify women at risk for of preterm birth; Virginia's governor has expanded Medicaid in the state; and the American Medical Association is expected to take a stance on over-the-counter birth control this weekend.
Preterm births occur in approximately 12 percent of all live births in the USA - and it is the cause of about 70 percent of newborn deaths, according to the American College of Obstetrics and Gynecology. It works by detecting the RNA that's circulating in the pregnant woman's blood, thereby providing vital information about the fetus's development.
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.
The test detected the variations in RNA in a pregnant woman's blood and estimated due dates within two weeks in almost half the cases.
The scientists used blood samples from 21 of them to build a statistical model, which identified nine cell-free RNAs produced by the placenta that predict gestational age, and validated the model using samples from the remaining 10 women.
In a related study of another 38 women, all at elevated risk of delivering preterm, the researchers identified seven nucleic acids that accurately classified women who delivered preterm up to two months in advance of labour. All the women had full-term pregnancies. The team used blood samples collected during pregnancy to identify which genes gave reliable signals about gestational age and prematurity risk. If larger clinical trials reproduce them, this kind of blood test could help save babies who would otherwise die because they were born prematurely, the researchers say.
They acknowledge that their studies will need verifiying in much larger, ethnically diverse cohorts, including women who aren't already known to be at risk of preterm birth.