TUESDAY, Aug. 21, 2018 (HealthDay News) -- That wearable oxygen monitor you bought for your baby could be feeding you bad information, researchers report.

Tests of two infant oxygen monitors sold directly to consumers have raised serious concerns about the accuracy of these devices, which are meant to keep an eye on a baby's heart rate and oxygen levels.

But one of the monitors, the Baby Vida, failed to detect low oxygen levels and kept displaying numbers that appeared normal, the researchers found. It also generated false warnings of low heart rate even though the baby was fine.

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The other monitor, the popular Owlet Smart Sock 2, inconsistently detected low oxygen levels in babies, said lead researcher Dr. Chris Bonafide. He's a pediatrician and safety expert at Children's Hospital of Philadelphia (CHOP).

"These are sold just as consumer products, yet are being compared to hospital-grade monitors," Bonafide said. "I think we've shown here that's not a fair claim to make. They're clearly not performing at the level of hospital-grade monitors."

The American Academy of Pediatrics (AAP) recommends against parents using any baby oxygen monitor, since research has shown that even the best hospital-grade devices cannot protect against sudden infant death syndrome (SIDS).

Monitor manufacturers tout the devices as a way to help new parents catch up on their sleep while still keeping an eye on their baby.

Instead, the devices could provide a false sense of security, said Dr. Rachel Moon, who chairs the AAP Task Force on SIDS.

"My main concern is people become complacent. They decide that since the baby's monitored it's OK for them to not practice safe sleep," said Moon, head of pediatrics for the University of Virginia School of Medicine. "Using a monitor is a lot easier than practicing safe sleep. And then if the monitors don't work, you're just in a horrible situation then."

The Baby Vida appears to be no longer on the market. Its website displays an error message, and the monitor is no longer available at Amazon or Walmart.

Owlet responded in a statement that its Smart Sock "is not a medical device and is intended for healthy babies. It is not intended to treat, cure or prevent any disease, including SIDS."

According to the statement, "Owlet recommends the same AAP guidelines for safe sleep and encourages using the device as a parents' peace of mind."

Bonafide and his colleagues tested the devices on 30 infants aged 6 months or younger in CHOP's cardiology and general pediatrics units during the last half of 2017.

Each baby wore a U.S. Food and Drug Administration-approved hospital-grade monitor on one foot and a consumer monitor on the other foot.

None of the 14 infants who experienced low oxygen levels according to the hospital-grade monitor had simultaneous low oxygen readings on the Baby Vida.

At the same time, the Baby Vida also falsely displayed slow heart rate in 14 babies who had a normal pulse, the findings showed.

"It had problems with false negative values and false positive values, in the same monitor," Bonafide said.

The Owlet device did detect low oxygen levels in all 12 patients who had their blood oxygen drop below normal, researchers said.

But the Owlet erroneously indicated that five of the 12 babies had normal oxygen levels at least once during these extended periods of low oxygen, the investigators found.

"Sometimes when those babies did have low oxygen saturation, the Owlet inconsistently would display normal oxygen saturation," Bonafide said.

Overall, the Owlet detected low oxygen levels accurately nearly 89 percent of the time. "If something is going wrong with a sick infant, you would want to know that 100 percent of the time," Bonafide said.

The findings were published as a research letter in the Aug. 21 issue of the Journal of the American Medical Association.

Owlet argues that this consumer test wasn't fair, because it compared their Smart Sock against another device used in hospitals. A true evaluation would have involved drawing blood from the babies, testing their blood gas levels in a laboratory and then comparing that to readings from the Owlet.

"The accuracy and performance of the Owlet Smart Sock is something that we take very seriously," Kurt Workman, co-founder and CEO of Owlet, said in a statement.

Bonafide said he's concerned these devices could needlessly scare parents by ringing an alarm when there's nothing wrong. He's also worried about false reassurance.

"A baby could actually be very sick and maybe the parent's instinct is to say, I really ought to bring this baby in, but maybe they check the number and the number can then falsely reassure, if they're dealing with a monitor that's not completely accurate," Bonafide said.

Parents who choose to use these monitors should discuss it with their pediatrician, he suggested.

"They should know what they're going to do if this monitor goes off in the middle of the night," Bonafide said. "Have that conversation with the pediatrician before that occurs so you can really have a plan in place."

More information

The American Academy of Pediatrics has more about safe sleep guidelines.