Based on fetal genetic material known as RNA circulating in a
mother's bloodstream, the tests can predict how much time is left in
a pregnancy with about the same accuracy and lower cost than current
methods, the study team reports in the journal Science.
"We have made a discovery on an important problem - but this is just
the beginning of the story, as our work needs to be validated in a
large (clinical trial) before it becomes medically useful," senior
study author Stephen R. Quake of Stanford University in California
told Reuters Health in an email.
Ultrasound, combined with a woman's estimate of her last menstrual
period, is typically used to estimate the week of pregnancy, which
is also the so-called gestational age of the fetus. But the scans
can be expensive and this method does not say anything about the
odds of a preterm birth, the study authors note.

A normal pregnancy lasts about 39 to 40 weeks, and births after 37
weeks' gestational age are considered full term. Millions of births
worldwide occur earlier than this, the researchers write, and
preterm birth is the leading cause of newborn death as well as later
health problems for these infants.
Quake's team previously showed that expectant mothers' blood
contains free-floating RNA molecules, each one a transcript of genes
that are active in both fetus and mother, and that the types and
amounts of these molecules changed over the course of pregnancy.
In the current pilot study, they found that a combination of only
nine RNAs could accurately predict the time remaining until delivery
for both first-time mothers and women who had previously given
birth.
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The blood test's accuracy, within 14 days of the actual gestational
age at delivery, was similar to that of ultrasound measurements. An
added benefit is that the blood test, unlike ultrasound, doesn't
rely on the woman's recollection of her last menstrual period.
The researchers also used a separate set of RNAs to identify women
who were at risk of preterm delivery. This test predicted preterm
and full-term births with an accuracy exceeding 80 percent, the
study found.
"The preterm birth result is important because of the tremendous
potential impact on human health - something like 15 million babies
each year are affected, and currently there are no good ways to
predict who is at risk," Quake said.
The researchers believe that similar blood tests can also be
developed to identify and monitor fetuses with congenital defects
that can be treated even before birth.
SOURCE: https://bit.ly/2JoQQwN Science, online June 8, 2018.
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