Scientists have developed a new blood test for pregnant women that could accurately detect whether their pregnancies will end in premature birth.
The technique can also be used to estimate a foetus' gestational age - or the mother's due date - as reliably as and less expensively than ultrasound.
The test, described in the journal Science, could help reduce problems related to premature birth, which affects 15 million infants worldwide each year.
Until now, doctors have lacked a reliable way to predict whether pregnancies will end prematurely, and have struggled to accurately predict delivery dates for all types of pregnancies, especially in low-resource settings.
The tests measure the activity of maternal, placental and foetal genes by assessing maternal blood levels of cell-free RNA, tiny bits of the messenger molecule that carry the body's genetic instructions to its protein-making factories.
The team used blood samples collected during pregnancy to identify which genes gave reliable signals about gestational age and prematurity risk.
"We found that a handful of genes are very highly predictive of which women are at risk for preterm delivery," said Mads Melbye, a visiting professor at Stanford.
The gestational-age test was developed by studying a cohort of 31 Danish women who gave blood weekly throughout their pregnancies. All the women had full-term pregnancies.
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.
The estimates of gestational age given by the model were accurate about 45 per cent of the time, which is comparable to 48 per cent accuracy for first-trimester ultrasound estimates.
Measuring cell-free RNA in mothers' blood also could provide a wealth of new information about foetal growth, said former Stanford postdoctoral scholar Thuy Ngo.
"This gives a super-high resolution view of pregnancy and human development that no one's ever seen before. It tells us a lot about human development in normal pregnancy," she said.
To figure out how to predict preterm birth, the researchers used blood samples from 38 American women who were at risk for premature delivery because they had already had early contractions or had given birth to a preterm baby before.
These women each gave one blood sample during the second or third trimester of their pregnancies. Of this group, 13 delivered prematurely, and the remaining 25 delivered at term.
The scientists found that levels of cell-free RNA from seven genes from the mother and the placenta could predict which pregnancies would end early.
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