Blood Test to Predict Pregnant Women's Due Date

Blood Test (Credit: Pixabay)

A new blood test for pregnant women detects with 75-80% accuracy whether their pregnancies will end in premature birth. The technique can also be used to estimate a fetus’ gestational age — or the mother’s due date — as reliably as and less expensively than ultrasound.

Having an early ultrasound to figure out when your child will be born is something most people take for granted. But for many women living in countries with poor-quality healthcare, ultrasounds are actually rarely available, or for some, too expensive to afford. 

But a new study published in Science, suggests that we’ll have a cheaper and easier way to pin down the due date in the future: a blood test. 

Researchers from Standford Medicine in collaboration with scientists from Denmark, Pennsylvania, and Alabama, recruited 31 Danish women to take part in their study. 

Each woman donated a weekly blood test throughout their pregnancy, that the researchers used to study bits of cell-free RNA — the messenger molecules that carry the body’s genetic instructions to its protein-making factories — taken from genes belonging to the mother, fetus and placenta. As the women’s pregnancies progressed, they noticed that the levels of RNA from certain genes found in the blood changed, too.

“We found that a handful of genes are very highly predictive of which women are at risk for preterm delivery,” said Mads Melbye, MD, visiting professor of medicine, and one of the senior authors of the study. 

Measuring the cell-free DNA in mother’s blood could also provide a wealth of new information about fetal growth, said lead author, and former Stanford postdoctoral scholar Thuy Ngo, PhD. 

They researchers used blood samples from 21 of the women to roughly work out a statistical model that predicted how pregnant a woman was, based on nine cell-free RNA genes sourced from the placenta.

In the remaining 10 women used to test the model, they were able to predict the gestational age of the fetus with 45% accuracy, meaning they were within 14 days of the actual due date (all 31 women had normal deliveries after 37 weeks).

That might not sound very precise, but ultrasound readings in the first trimester only have an average accuracy of 48%, according to the researchers.

“This gives a super-high resolution view of pregnancy and human development that no one’s ever seen before,” Ngo said. “It tells us a lot about human development in normal pregnancy.” 

The test, if further refined, could also tell us a lot more about the growing fetus later on in the pregnancy, unlike ultrasounds, which become less accurate in the second and third trimesters.