(Reuters Health) - Women could soon know how far along they are in pregnancy and their risk of premature delivery using simple blood tests, researchers say.

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.

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: bit.ly/2JoQQwN Science, online June 8, 2018.