Largest risk factor for sudden infant death is bed-sharing, particularly among very young babies, US researchers said on Monday.
Sixty-nine percent of babies who died suddenly were sharing a sleeping space with another person when they died, said the report in the journal Pediatrics.
The findings were based on government data regarding 8,207 sleep-related infant deaths from 24 states from 2004-2012.
Researchers found that the risks were different for infants up to age three months than they were for those aged four to 12 months.
Younger infants who died were more likely to have been bed-sharing (73.8 percent vs. 58.9 percent).
Bed-sharing was defined as sleeping on an adult's bed either near or on another person.
Older babies who died while sleeping were more likely to have been discovered on their bellies with objects like blankets or stuffed animals in their sleeping area.
The American Academy of Pediatrics recommends that babies sleep on a firm surface, in a crib near their parents or caregivers, but not in the same bed in order to avoid the danger of accidental suffocation.
Babies should also be placed on their backs to go to sleep. Pillows, blankets and toys should be kept out of the baby's bed, the AAP has said.