On the heels of a study that showed infant deaths from critical congenital heart defects fell by one-third in eight states that first mandated a newborn screening test, experts now look forward to technological improvements in the test so that more babies’ lives can be saved.

“I think that the state mandates and the fact that babies are being screened is going really well,” said Dr. Marci Sontag, associate director of Newborn Screening Technical Assistance and Evaluation Program, or NewSTEPs, which collects data on newborn screening across the country. “But does the screen need to be adjusted? Yes. There are nuances that could be addressed.”

Data collection and analysis from the screening test, called pulse oximetry, could be improved, said Sontag. As it is, there are some unique scenarios of a test result, such as when readings differ between a hand and foot. Her big worry is that some babies who need referrals are being missed.

“I want to know that states know who’s being screened, and then where those kids [with low oxygen levels] go,” Sontag, an epidemiologist, said. “Did they get an echo[cardiogram], did they get treatment, are babies being missed?”

Pulse oximetry measures oxygen levels in the blood by placing a small probe on the hand and foot of a newborn. A reading of 95 percent to 100 percent is normal for a healthy baby, but a blood oxygen saturation level below 95 percent may require further testing to check for a heart problem.

But pulse oximetry isn’t perfect, experts said. For example, if an infant is moving too much during the screen or the probe isn’t attached correctly, the results may not be as accurate. Or, and perhaps more importantly, “many children with significant [critical congenital heart defects] may not have low enough oxygen levels to be detected,” said Dr. Matt Oster, a pediatric cardiologist with Children’s Healthcare of Atlanta.

Still, Sontag is hopeful that improvements are coming. She said several private companies are working to enhance their technology through methods such as refining algorithms to flag babies who score in the normal range but whose hand and foot scores are more than 3 percentage points apart, which requires further evaluation. The goal is to take away any guesswork so that all babies who need further evaluation can be identified.

An estimated 40,000 babies are born each year with congenital heart defects, and about one in four has a critical congenital heart defect that requires surgery within a year. But historically, many babies left their birth hospitals with their heart defect undiagnosed and therefore missed their window for surgery.

The recent study, published in December in JAMA, was the first to analyze data from the eight states that had mandated pulse oximetry by June 2013.

The dramatic drop in infant deaths was “larger than what we anticipated,” said study coauthor Dr. Scott Grosse, a health scientist at National Center on Birth Defects and Developmental Disabilities at the Centers for Disease Control and Prevention. “If it had been half as large, we still would have been impressed.”

As of 2017, all states except Idaho and Kansas mandate newborn screening for critical congenital heart disease, according an editorial that accompanied the study. Even so, most hospitals in states that do not require it still conduct the test, experts said.

“What this study was able to show is that [pulse ox screening] does make a difference,” said Oster, who also coauthored the JAMA study.

Four deaths were prevented for every 100,000 births, the study showed. The researchers took that finding a bit further, writing that pulse oximetry could save the lives of 120 infants every year if screening was mandated nationwide.

“The study showed that while everyone thought and hoped that the screening would save lives, it really did,” Oster said. “It’s a great example of a public health success story.”