A mother puts booties on an infant in Miami, Florida in 2006. Very young babies face a small risk of sudden death when seated, and not only when they are lying down, according to a study published online by Archives of Disease in Childhood, a British journal.[AFP]

The findings are based on an analysis of cases of sudden, unexpected deaths that occurred among infants up to the age of 12 months in Quebec, Canada, between 1991 and 2000.

Of 508 fully investigated deaths, 17, or 3.3 percent, occurred in babies who had been placed in seats, most often in car seats. The relative risk was much higher among babies who were less than a month old.

The authors, led by Aurore Cote at the McGill University Health Center in Montreal, say the risk was relatively small and do not call car-seat safety into question.

But extra care should be taken for very young babies in any type of infant seat, they say.

Last December, a paper in the British Medical Journal (BMJ) by doctors at New Zealand's University of Auckland recommended that parents not let very young babies sleep unattended in standard car safety seats.

They examined the cases of 43 local babies who had turned "blue" from lack of oxygen and had needed medical attention.

Nine of these infants had been restrained in a car safety seat that was suitable for their age.

When the experts reconstructed the scenes, using the infant's own car seat, they found the baby's head was invariably flexed forward. Its jaw pressed down on its chest, which caused a narrowing of the upper airway and led to breathing difficulties.

Several factors could have aggravated their difficulties, the main one being that the infants were very young -- average age five weeks -- and were thus at a stage when head control was undeveloped.