A blood test could give a more exact baby due date, improve prenatal care: Study

When will a pregnant woman actually deliver her baby? Right now, it's pretty much an informed guess -- and that's not just inconvenient, assumptions about when a baby is due can also lead to extra medical procedures for both the mother and the baby.

A new study, published in Science Magazine, tried a new method of predicting when a baby is due -- using a simple blood test that could be more accurate than the current method of using the expectant mother's estimate of missed periods, paired with a series of ultrasounds.

"Currently, the best tool that clinicians have to understand pregnancy is ultrasound," the co-author of a new study Mira Moufarrej, researcher at Stanford University, told ABC News. "While ultrasound gives us a good idea of how far along a given pregnancy is ... what it doesn’t tell us is when a given woman will deliver."

Not knowing the exact number of weeks of a pregnancy means doctors may think a baby is overdue when it’s not -- and that can lead to unnecessary induction of labor, C-sections, extended postnatal care and increased medical expenses.

The leading cause of complications and neonatal death is preterm birth, which affects approximately 15 million births a year worldwide.

Preterm births occur in approximately 12 percent of all live births in the U.S. -- and it is the cause of about 70 percent of newborn deaths, according to the American College of Obstetrics and Gynecology.

Two-thirds of preterm births occur spontaneously, without medical induction, according to the study.

But, with a more precise delivery date, doctors could prepare earlier pregnancies that are at risk.

In this pilot study, researchers looked at 31 healthy pregnant women and showed that the blood test (which looked at genetic RNA particles circulating in the blood) was able to predict gestational age and identify women at risk for preterm delivery, all from the same blood sample, with 75-80 percent accuracy. That’s as reliable as an ultrasound, and much quicker and cheaper. In a study of 38 women at risk of preterm delivery, RNA markers were also identified.

Moufarrej said that the test “would allow us to predict up to two months in advance of delivery a really important risk during pregnancy -- spontaneous preterm birth.”

"RNA corresponding to placental genes may provide an accurate estimate of fetal development and gestational age throughout pregnancy," the report found.

The pilot study was promising, but before this can be a new standard of care, a larger sample size and a blind trial would be necessary.

Moufarrej expects those trials could come in the next five years.

"In the long run, non-invasive blood tests like we describe in the paper -- that predicts gestational age and risk of preterm delivery -- would make prenatal care more accessible and affordable," she said, "hopefully leading to healthier pregnancies and healthier babies."

Eric M. Ascher, D.O., is a third-year family medicine resident from New York working in the ABC News Medical Unit.