Babies should never be allowed to sleep in car safety seats when the seat is not in a car, researchers say after a new study showing a link to decreased oxygen levels.
Dr Christine McIntosh and her colleagues have also warned that babies' time in car safety seats should be kept to a minimum, after the latest findings in their long-running research.
The researchers, from Auckland University and the Cot Death Association, have previously shown a reduction in mild breathing problems in babies whose car safety seat was fitted with a simple foam insert with a slot for the back of the head.
Babies' heads are larger, relative to the body, than adults' heads, and protrude behind the line of the back.
The commercially available insert helps to keep the baby's body forward. It also allows the head to remain upright even when the infant is asleep, rather than slumping forward, which can obstruct breathing when the chin is on the chest and pushed back.