Blood test can predict a baby’s due date

Parents have long yearned for a simple test that could accurately predict a mother’s due date, and her risk of a premature birth.

Now, using powerful genetic techniques, Stanford scientists are closing in on that dream with a preliminary tool that requires only a pregnant woman’s blood sample.

Acting like a molecular stethoscope, the test detects with about 75 percent accuracy whether the baby will be born prematurely, according to the new research, published in the current issue of the journal Science.

The same approach also can be used during the first trimester to estimate the due date with about 45 percent accuracy — a rate similar to ultrasound, a more expensive and invasive test.

The innovation could “alert us to which women are at risk so

they can be appropriately cared for,” said Stanford professor of bioengineering Stephen Quake, a senior author on the paper, in a prepared statement. “Hopefully that will give them a safer and more comfortable pregnancy, both physically and psychologically.”

There are reasons to be cautious about the news. The test was tried in fewer than 100 women. And it focuses on just a few genes; other genes may also prove to be important.

Calling it “an exploratory study,” the American College of Obstetrics and Gynecology called the research “too premature to say anything about. Ultimately, it needs a lot more investigation to determine if it will be clinically useful.”

But it enlists an affordable and convenient technique that, if proven further, could transform the monitoring of at-risk mothers and fetuses, saving lives. Preparing for an imminent birth can boost the survival rates of fragile infants. Predicting who is likely to have a preterm baby — and someday preventing early labor — would be even better.

There is currently no reliable way to predict when a pregnancy will result in premature birth, one of the world’s primary causes of fetal sickness and death, Dr. Kecia Gaither, director of Perinatal Services at NYC Health + Hospitals in the Bronx, New York, said in an email.

And it is difficult to accurately predict delivery dates, she said. Doctors currently rely on ultrasound imaging or the mother’s estimate of her last menstrual period to predict the gestational age of a fetus. But ultrasound can be expensive or unavailable. Estimates of menstrual periods can be imprecise.

Inaccurate estimates of due dates can sometimes lead to unnecessary induction of labor and cesarean sections, with pain and increased medical expenses.

“For any country, the cost factor — socially, fiscally, medically — would be markedly reduced if there were to be such a technological methodology,” Gaither said.

“The medical community, particularly the neonatal/perinatal community, would be exceedingly welcoming to have such a useful test,” she said.

If the results can be duplicated in a larger and more diverse population, the tool could be “a game changer,” said Dr. John Thoppil, president-elect of the Texas Association of Obstetricians and Gynecologists who teaches at Texas A&M University’s College of Medicine.

“For the most part, we can’t tell who is at risk for prematurity despite all the marvels of modern medicine,” he wrote in an email. “The first step in decreasing our premature births is identifying who is most at risk.”

The Stanford test detects the activity of genes in the mother, fetus and placenta by measuring levels of cellfree RNA, the loose pieces of genetic material that course through our veins, cast off by dying cells. Like a message in a bottle, the genes give reliable signals about fetal growth, gestational age and prematurity risk.

The Stanford team read these signals not just from the mom’s cells but also from the fetal cells that flow into the the mother’s blood. The genetic activity reveals physiological changes in the tissues and organs of both the mother and the baby — and clues of distress that can precede premature delivery.

“We found that a handful of genes are very highly predictive of which women are at risk for preterm delivery,” senior author Dr. Mads Melbye, a visiting professor of medicine at Stanford and president of the Statens Serum Institute in Copenhagen, said in a prepared statement. The lead authors are former Stanford postdoctoral scholar Thuy Ngo and Stanford graduate student Mira Moufarrej.

The team arrived at their findings by analyzing weekly blood samples from 31 Danish women over the course of their pregnancies to identify cell-free RNA indicative of the fetuses’ gestational age. Based on this data, the blood test they developed predicted the gestational age — when the birth occurred, within two weeks of the estimated due date — with 45 percent accuracy, which is comparable to ultrasound results of 48 percent.

When comparing the cellfree RNA of seven genes, they were able to identify six of eight pre-term births and 25 out of 26 full-term births in a study of American women during the second or third trimester of their pregnancies.

Before the new test is available for widespread use, it needs to be validated in research of larger numbers of pregnant women, according to the team.

The free-floating genetic material has proven to be a powerful tool for detecting other problems as well.

One simple blood test, also developed by Quake’s team, can tell newly pregnant women if they are carrying a child with Down syndrome. Developed in 2008, the test is now used by more than 3 million pregnant women a year.

Another blood test, still in development at the University of Washington, studies cell-free genetic material in an effort to detect cancer.

“Hopefully that will give them a safer and more comfortable pregnancy, both physically and psychologically.” — Stephen Quake, Stanford professor of bioengineering, on what the blood test can do for pregnant women at risk of premature birth