A new study, conducted in 11 counties in California, is the first to examine the relationship between infant sleeping position and SIDS in a diverse U.S. population.
"Infants placed in an unaccustomed prone or side sleeping position had a higher risk of SIDS than infants who were always placed prone or on the side," writes lead author De-Kun Li, MD, a researcher with the Kaiser Foundation Research Institute in Oakland, Calif. His study appears in the American Journal of Epidemiology.
"These findings reinforce the importance of placing infants on their backs at all times," says Duane Alexander, MD, director of the National Institute of Child Health and Human Development, in a news release.
The incidence of SIDS has declined more than 50% since 1992, when the American Academy of Pediatrics recommended that infants be placed on their backs to sleep. Before the Kaiser study, evidence of the link between stomach sleeping and SIDS risk was based largely on overseas studies, where populations and cultural practices are different from those in the U.S.
In their study, Li and colleagues conducted in-person interviews with the mothers of 185 SIDS cases and 312 randomly selected mothers who served as controls. They asked mothers about the position in which the infant had last been put down to sleep, the position in which the infant was found, changes in sleep position since birth, during the two weeks before death, and on the death date.
Infants last placed on their sides for sleep were more likely to die of SIDS than infants placed on their backs.
Also, the risk of SIDS was significantly increased if infants turned from their sides to their stomachs during sleep.
Though the reason is not clear, researchers say that the instability of the side position makes it more likely for babies who are placed to sleep in this position to roll over onto their stomachs.
A pattern also emerged when the researchers looked specifically at the position in which an infant was last placed to sleep compared with their usual sleeping position. If the infant was usually placed to sleep in the low-risk position -- on the back -- but was placed to sleep in a high-risk position -- on the stomach or side -- the SIDS risk was 7 to 8 times greater than that of an infant who was always placed to sleep on his or her back.