According to a study in the Journal of Pediatrics there have been 47 deaths recorded by the US Consumer Product Safety Commission (CPSC) between 2004 and 2008 that occurred in car seats, swings, slings, strollers, and bouncers. Of those, 31 occurred in car seats. The cause was strangulation from the straps or asphyxiation. Why you ask? 1. Children were not properly buckled (harness was loosened or not buckled appropriately) and the child moved in the seat getting caught up in the straps and 2. the car seat was placed on an elevated surface and fell over, causing injury and death to the child.
The American Academy of Pediatrics recommends that these types of devices not be used for sleeping arrangements for the baby. Babies need to be in a safe, FLAT environment (unless otherwise directed by your pediatrician) to reduce the chances of SIDS or Sudden Infant Death Syndrome.
As you can see from the picture below the parents loosened the harness and moved the harness retainer clip (chest clip) down. The infant can wiggle and move and potentially get caught up in the straps.
WRONG WAY TO HARNESS A BABY!!!