Half of babies are at risk of sudden infant death syndrome (SIDS) because they are put to bed with unsafe bedding, blankets and pillows.
Sleeping with loose bedding or soft objects poses a risk of suffocation in babies because they can construct a baby's airway or can get trapped over a child's head.
But despite years of advice, a study by the American Academy of Paediatrics (AAP) found that half of babies are still put in cots with 'potentially hazardous bedding'.
The data comes from the National Infant Sleep Position study which looked at the type of bedding chosen by parents from 1993 to 2010.
The AAP advises parents to put their babies to sleep in a cot with no loose bedding or soft objects, including cuddly toys, under or over the infant.
Experts advise using a firmly tucked in sheet, or a baby sleeping bag, instead.
While sudden infant syndrome deaths have declined in recent years, they still totaled around 2,000 deaths in the US in 2010.
The suffocation rate doubled from 2000 to 2010, when around 640 infants died from accidental sleep-related suffocation.
In the UK in 2012, 221 infant deaths were attributed to SIDS.
The team of researchers found that over the 17-year period, the use of loose bedding did decline but remained a common practice.
The rate of loose bedding use averaged around 86 per cent in 1993 to 1995, but declined to 55 per cent in 2008 to 2010.
Teenage mothers were found to be most likely to use the dangerous bedding (83.5 per cent), while those babies born at full term were least at risk (55.6 per cent).
The study also found the at-risk bedding was most likely used for infants who slept in adult beds, those put to sleep on their sides, or babies who shared a cot or bed with others.
The authors concluded that while the numbers have improved significantly, babies are 'still being put to bed in an unsafe sleeping environment; about half still sleep with blankets, quilts, pillows and other hazardous items'.
Study co-author Marian Willinger, a SIDS expert at the National Institute of Child Health and Human Development, said these infant deaths 'are tragic and they're just not necessary'.
The AAP said it is vital parents 'know and understand the risk factors associated with this dangerous practise in order to help reduce the number of sleep-related infant deaths'.
Lucy McKeon, research and information manager at The Lullaby Trust, said: "This new study suggests parents are using loose bedding which is considered less safe than well-fitted blankets or a baby sleep bag.
"A simple mattress in your cot with no loose bedding or bumpers is the safest sleeping place for a baby."
The study was published today in the journal Pediatrics.
ADVICE FOR PARENTS FROM THE LULLABY TRUST
Place your baby on his back to sleep.
Put your baby to sleep in a separate cot or Moses basket in the same room as you for the first six months.
Use a firm, flat, waterproof mattress in good condition
Don't cover your baby's face or head while sleeping or use loose bedding, such as quilts, blankets, pillows or cot bumpers.
Evidence-based advice is available on The Lullaby Trust website, www.lullabytrust.org.uk.
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