Parents should not leave young infants sleeping in car seats for long periods of time, said a Quebec coroner who looked into the death of a two-month-old boy who suffocated when his mom placed him in a car seat after a restless night.

The recommendation comes two years after Montreal researchers warned very young babies are vulnerable to sudden infant death syndrome if they spend too much time in a seated position.

"The car seat is for the car. It is not for the bed or sleeping. It is for a car," said coroner Dr. Jacques Robinson on Wednesday.

'The head of the baby is heavier than the body. The neck muscle is not straight enough to let the neck rise. So, it falls.' —Dr. Jacques Robinson, Quebec coroner

The case that prompted the coroner's recommendation happened in February 2008 in Pointe-Claire on Montreal's west island.

A mother woke at 3 a.m. to feed her baby who was crying. She put the baby back to sleep in his crib. At 6 a.m., the baby started crying again.

The mother used a trick she had used before: she placed the baby in his car seat and then put the car seat in the crib.

An hour later, the mother checked in on the baby and found that he wasn't breathing. His eyes were glassy and his skin had a white, waxy appearance.

The mother called 911, and the parents started CPR on the baby. The baby was pronounced dead in hospital.

Robinson determined the baby died of asphyxiation due to an obstruction of his upper airway and blamed the baby's cramped posture in the seat for reducing his ability to breathe.

"The head of the baby is heavier than the body. The neck muscle is not straight enough to let the neck rise so it falls," said Robinson.

In his report, Robinson notes there are risks to leaving a child sleeping in any seated position. He encourages parents to put their children to sleep horizontally at all times, preferably in a crib.

He also advises parents to move their babies frequently when they are in a car seat in a vehicle. He recommends parents take their children out of the seat every hour while on a long trip.

Researchers find dangers with sleeping while seated

The coroner's findings are echoed in a study conducted by researchers at the McGill University Health Centre.

Researchers analyzed more than 500 sudden and unexpected deaths among babies under the age of one in Quebec between 1991 and 2000.

Seventeen (3.3 per cent) of the deaths occurred in babies who were seated, mostly in car seats.

The study was published in the online edition of the Archives of Disease in Childhood in 2007.