In a review of infant deaths that occurred while children were sleeping in sitting devices, researchers determined than more than 60% of the deaths were in car seats. The car seats were used as directed in less than 10% of those cases.

“While car seats are important when you’re traveling with an infant, it’s best not to have the infant sleep in the car seat when you’re at home,” says researcher Rachel Moon, MD, a pediatrician at the University of Virginia Children’s Hospital, in a release. “The safest place for a baby to sleep is on a firm, flat surface.”

Sleep-Related Infant Deaths in Sitting Devices

Moon and colleagues set out to shed light on a poorly documented category of infant deaths: deaths while sleeping in sitting devices, such as car seats and strollers. The American Academy of Pediatrics discourages allowing children to routinely sleep in such devices.

Of almost 12,000 infant sleep-related deaths reported between 2004 and 2014, approximately 3%—348 deaths—occurred in sitting devices, the researchers found. Car seats were the site of 62.9% of these deaths, but in the “great majority” of cases, the infant was not traveling in a car, the researchers report. Out of the total deaths in a sitting device, only .2% occurred in a vehicle that was in motion or temporarily parked. More than half of car seat deaths occurred at the child’s home.

While the researchers did not establish why the infants were in car seats when not traveling, they note that some parents may not be able to afford a crib or bassinet, or people may use the seats to hold the child while doing other tasks.

After car seats, the most common site for sleep-related infant deaths while sitting were bouncers, swings, and similar devices (122 deaths, 35.1%). Strollers were the site of 2% of deaths (seven of the 348).

Overall, nearly two-thirds of the deaths in sitting devices occurred while the devices were not being used for their intended purpose and in compliance with their instructions, the researchers report.

The researchers emphasize that their findings in no way call into question the safety of car seats when used as directed. Car seats are a “safe and effective way of transporting an infant and should always be used when transporting an infant in a motor vehicle, whether the infant is awake or asleep,” the researchers write.

The researchers have published their findings in the scientific journal Pediatrics. The study’s authors were Peter Liaw of UVA, Moon, Autumn Han of Missouri’s Capital Region Medical Center and Jeffrey Colvin of Missouri’s Children’s Mercy Hospitals and Clinics.

Funding for the Child Death Review Case Reporting System used in the study is provided by the Maternal and Child Health Bureau of the U.S. Department of Health and Human Services, grant UG7MC28482.