A new blood test that can estimate due dates may be on the horizon.
A new blood test that can predict preterm birth and estimate due dates may be on the horizon.

Despite the fact that only 5% of babies are born on their "due date," it remains one of the first questions asked when expecting. While knowing the estimated delivery date of a baby can help a family prepare for their new arrival, we all know that babies come when they are ready.

As it currently stands, a woman's estimate of her last menstrual period and ultrasounds are both used to determine gestational age. Ultrasounds during the first trimester are presently the gold standard for predicting due dates. However, in addition to being relatively expensive, ultrasounds also have a margin of error, which increases as the pregnancy progresses. They also have no way of predicting early spontaneous births.

Related: Why I Asked My Midwife to NOT Tell Me My Due Date

Led by researchers at Stanford University, scientists have recently discovered a way to use non-invasive blood tests to predict a woman's risk of premature birth, as well as to estimate a fetus's gestational age.

According to a press release from Stanford, the new blood tests can detect whether or not a pregnancy will end in premature birth with 75-80% accuracy. The blood test can also estimate a woman's due date with the same precision as an ultrasound. The new blood tests are described in a paper published this month in the journal Science.

The pilot study, which involved 31 healthy Danish women who gave blood weekly throughout their pregnancies, measured nine cell-free RNA molecules in the blood. Using a sophisticated statistical model, the researchers were able to estimate gestational age within 14 days at delivery for 45% of the women in the study. In comparison, when using ultrasound, the researchers were able to predict gestational age in 48% of the women.

Related: Ultrasounds During Pregnancy: Helpful or Harmful?

Utilizing blood samples from another 38 American women who were at high risk for premature birth, the scientists found that levels of cell-free RNA from seven maternal and placenta genes could predict up to two months in advance which infants would be born early.

"Essentially, the findings are that you can measure gestational age and predict risk of preterm delivery in this pilot study," first author Mira Moufarrej told CNN. "The next steps would be to get an ethnically diverse cohort of women prospectively collected and then see if these findings validate there, both findings about gestational age and the ones about preterm delivery," she continued.

If the smaller pilot studies can be replicated in a larger, more diverse group, the implications could be enormous. The blood tests could provide a more cost-effective and accurate way to validate due-dates, as well as to be the first blood test to predict preterm birth.