March 22, 2000 (Indianapolis) -- Sleeping on the tummy, or prone position, has been the most commonly identified risk factor in sudden infant death syndrome (SIDS). A study in this month's journal Archives of Disease in Childhood suggests one reason why.
The study shows that sleeping on the stomach has a measurable effect on the body's ability to control the size of its blood vessels, such as arteries and veins, which causes the blood vessels to dilate, or expand. This affects the infant body's ability to control its circulation.
"We wanted to do this study as we believe that sudden infant death syndrome is possibly linked with a problem with the circulation," says lead author Angeline Chong, MD, from the department of pediatrics at Rotunda Hospital in Dublin, Ireland, in an interview with WebMD. "Traditionally, research has focused on finding a respiratory cause to sudden infant death syndrome."
Forty-four full-term infants were studied during an overnight sleep. Recordings were made while the infants were horizontal and asleep on their backs and while they were asleep in a face-down position. Recordings were repeated after their heads were tilted 60 degrees in each sleeping position. Blood pressure, heart rate, and shin and abdominal wall skin temperatures were measured.
"We found in our study that babies who were lying on their tummies were more likely to drop their blood pressure, have a faster heart rate, and a higher skin temperature on their legs, which to us meant that the control of circulation was not as good when babies lie on their tummies," says Chong. Problems in circulation could cause blood not to reach vital organs such as the heart, lungs, and brain while an infant is sleeping. "We are still unclear as to why babies die of SIDS, and need more research into this area. Our findings will hopefully lead to other scientific works."
Emphasizing the uncertainty of what causes SIDS, Warren G. Guntheroth, MD, professor of pediatrics (cardiology) at the University of Washington in Seattle, notes that most SIDS experts think that heat stress plays a major role in the death of these infants. The outcomes observed by the researchers in this study could just as easily be related to the body's reactions to the buildup of heat, Guntheroth says, adding that dilation of the blood vessels to help the body cool off is an example.
"They have established no new category of risk in SIDS deaths," says Guntheroth in an interview with WebMD. "Their findings of increased skin temperature reinforce the idea put forth by myself and others that heat is the single most neglected risk factor in SIDS. This does, however, give yet another reason to place babies on their backs instead of their bellies."
The American Academy of Pediatrics recommends that infants not be placed for sleep in a face-down position. Sleeping on the back has the lowest risk and is preferred, and sleeping on the side -- while not as safe as sleeping on the back -- has a lower risk than sleeping on the tummy.
- Sleeping on the stomach is the most commonly identified risk factor for sudden infant death syndrome (SIDS).
- Researchers have found evidence that poor circulation control may contribute to SIDS, as babies sleeping on their stomachs are more likely to experience a drop in their blood pressure, faster heart rate, and higher skin temperature on their legs.
- Though scientists still do not know what causes SIDS, many believe that heat stress does play a role in the death of these infants.