A large portion of sleep-related deaths occur when infants are placed on sofas, according to a new study that also found certain behaviors are linked to those deaths.

About one in eight sudden and sleep-related deaths among infants are occurring on sofas, according to researchers. They also say that deaths were more common among infants sleeping on a sofa with someone else, found on their side or exposed to tobacco while in the womb.

“We did this study simply because there wasn’t a lot of data out there already about what are the factors related to sleep-related deaths on sofas,” said Dr. Jeffrey Colvin, one of the study’s authors and a pediatrician at Children’s Mercy Hospitals in Kansas City, Missouri.

The researchers analyzed data collected between 2004 and 2012 from 24 states, on the sleep-related deaths of 7,934 infants aged 12 months or younger.

Overall, 12 percent of the deaths occurred while the infant was sleeping on a sofa. Compared to other sleep-related deaths, those occurring on sofas were about 20 percent more likely to have an ill-defined cause of death and 90 percent more likely to be classified as suffocation.

Infants who died while sleeping on sofas were more than twice as likely to be sharing the space with someone else, the researchers found.

“We found that one in eight of (sleep-related) deaths occurred on the sofa and nearly 90 percent to those deaths occurred when an adult was sharing that sofa with the infant,” Colvin said.

The infants who died while sleeping on sofas were more likely to be new to sleeping on that surface, compared to infants who died elsewhere.

“That location was not the infant's usual sleep location,” Colvin said. “That brings up the possibility that the sofa was likely being used for a nap rather than overnight sleeping.”

The infants were also more likely to be found on their side. Surfaces often slope toward the back of the sofa allowing infants to easily roll and wedge between the cushions, the researchers write in the journal Pediatrics.

Additionally, the researcher found infants who died while sleeping on sofas were more likely to have been exposed to tobacco in the womb, compared to infants who died while sleeping on other surfaces.

Colvin said it’s difficult to explain the connection between smoking and sleep-related deaths among infants on sofas.

“I think the message for parents is that the sofa is an inherently dangerous place for an infant to sleep,” he said. “It’s a soft sleeping surface with pillows and blankets.”

The American Academy of Pediatrics recommends that infants sleep on a flat firm surface, according to the researchers.

"There is simply nothing about sofas that follow the ABCs of safe sleeping,” Colvin said. Those ABCs are that babies sleep Alone on their Backs in Cribs, he added.

Colvin added that parents should also know that sudden infant deaths can occur during naps and not just during overnight sleeping.

“An unsafe sleep environment is unsafe whether it’s night or day and whether the adult is awake or asleep,” he said.