Will my baby choke if placed on the back to sleep?
No. Healthy babies naturally swallow or cough up fluids—it's a reflex all people have. Babies may actually clear such fluids better when sleeping on their backs because of the location of the opening to the lungs in relation to the opening to the stomach. There has been no increase in choking or similar problems for babies who sleep on their backs.
When the baby is in the back sleep position, the trachea (tube to the lungs) lies on top of the esophagus (tube to the stomach). Anything regurgitated or refluxed from the stomach through the esophagus has to work against gravity to enter the trachea and cause choking. When the baby is sleeping on its stomach, such fluids will exit the esophagus and pool at the opening for the trachea, making choking much more likely.
Cases of fatal choking are very rare except when related to a medical condition. The number of fatal choking deaths has not increased since back sleeping recommendations began. In most of the few reported cases of fatal choking, an infant was sleeping on his or her stomach.