If you thought Sudden Infant Death Syndrome (SIDS) only occurs when babies are lying down, think again.

Very young babies also face a small risk of sudden death when seated — as in a car seat. Babies less than a month old are the most vulnerable according to a study published in the journal, Archives of Disease in Childhood.

In fact, babies less than a month old were over 7 times more likely to die suddenly when seated than older babies. Surprisingly, premature babies were not at greater risk than full-term babies.

The McGill University Health Centre researchers analyzed 508 unexplained sudden deaths of infants (up to 12 months old) in Quebec, Canada, from 1991 to 2001.

Seventeen, or 3.3%, of the deaths occurred when babies were seated — usually in car seats. Ten of those deaths were unexplained.

Although the death rate was small, even one baby dying is too many.

A previous study by doctors at New Zealand’s University of Auckland might shed some light on why this happens. That study was published in the British Medical Journal in December 2006.

They studied 43 cases where babies had turned blue from lack of oxygen and needed medical help.

The babies were an average of 5 weeks old. Nine of them had been in car seats that were considered to be suitable for their age.

The researchers found that the babies in car seats had their heads down with their jaws pressed on their chests. That led to compressed airways and trouble breathing.

The doctors believed that the babies’ lack of head control caused the problem.

While the experts stress that you must use a car seat for your infant’s safety, you should take extra care with very young babies in any kind of infant seat.