March 27 (HealthDay News) -- Sleeping position doesn't affect the extent of head flattening in infants, U.S. researchers say.
They examined risk factors for the severity of asymmetrical head shape, known as deformational plagiocephaly (DP), in a study involving 434 infants with the condition.
Since the early 1990s, parents have been encouraged to place babies on their backs to sleep to reduce the risk of sudden infant death syndrome (SIDS). Since then, there's been an increase in DP, which affects as many as one in six infants, according to background information in the study.
Previous studies have looked at possible risk factors -- including sleep position, prematurity and development delay -- for the development of DP, but the influence of each of those factors on the degree of asymmetry has not been clarified. That was the goal of the new study, by researchers at Hasbro Children's Hospital and Children's Hospital Boston, who found that sleep position does not affect the severity of head flattening.
"We found a trend toward less flattening in infants who slept prone [face downward], or in positions that were alternated," Dr. Albert Oh, a professor of surgery at the Alpert Medical School at Brown University, said in a Hasbro Children's news release. "Interestingly, however, while supine [on the back] positioning has been a well-established risk factor for the development of plagiocephaly, we were not able to demonstrate a logical correlation to indicate more severe flattening from the supine position."
The researchers did find that lower gestational age was associated with more severe flattening and that boys were more likely than girls to have severe flattening. They also found an association between multiple-birth pregnancies and the degree of head asymmetry.
"In our study, infants with DP who were the product of a multiple-birth pregnancy were disproportionately higher than in the general population and greater than in previous studies," Oh said. "This was the only pregnancy-related variable we found to be associated with the severity of DP of the eight different variables we assessed."
There was no evidence that special devices to prevent or treat DP had an effect on head flattening, which calls into question the use of the devices, the researchers said.
The study was published in the March issue of The Journal of Craniofacial Surgery.
SOURCE: Hasbro Children's Hospital, news release, March 2009