Unattended infants could be at risk of breathing difficulties such as apnoea — where breathing briefly stops — while restrained in a specialist seat for prolonged periods of time.
Nine babies who suffered from such problems were described as going “blue,” appearing “scrunched up” and “not breathing”.
The study, carried out by scientists in New Zealand and published in the British Medical Journal, looked at babies referred to the Auckland Cot Monitoring Service between July 1999 and December 2000.
The nine babies — aged between three days and six months — were left to sleep restrained in a car seat.
When the scene was reconstructed, scientists found the children’s heads bent forward with the jaw pressed on the chest, narrowing the airway and causing breathing problems.
Professor Alistair Gunn, associate professor at the Departments of Physiology and Paediatrics, University of Auckland in New Zealand, said parents should not leave babies for “excessive periods” in car seats.
But he said modifying seats to stop a child’s head bending forward could help.
“Infant car safety seats are vital to protect young infants in motor vehicle accidents,” he said.
“However, infants with certain health conditions are at risk of oxygen de-saturation and apnoea — temporary suspension of breathing — while they are restrained in recommended semi-reclining infant car seats.”
Michael Hayes, from the Child Accident Prevention Trust, said special seats for children reduced injury by 90%-95%.
He said 24 children aged under 10 died while travelling in cars in 2005 and 226 were admitted to hospital.