Researchers funded by the National Institutes of Health have identified three principal factors linked to whether caregivers place infants to sleep on their backs. Those three factors are: whether they received a physician's recommendation to place infants only on their backs for sleep, fear that the infant might choke while sleeping on the back, and concerns for an infant's comfort while sleeping on the back.

A large body of research has shown that placing infants on their backs to sleep reduces the risk of Sudden Infant Death Syndrome (SIDS), the leading cause of death during the first year of life in the United States.

"Placing infants on their backs for sleep remains the single most effective means we know to reduce the risk of sudden infant death syndrome," said Marian Willinger, Special Assistant for SIDS research at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), which funded the analysis. "For the vast majority of infants, concerns about choking while back sleeping are unfounded."

Dr Willinger noted that certain conditions might prompt a physician to consider recommending against back placement. However, such recommendations are arrived at only after careful deliberation and after taking into account all the potential risks and benefits for the infant involved.

The survey also found that after increasing steadily, the proportion of infants placed to sleep on their backs levelled off in the years since 2001.

The study appears in the December issue of Archives of Paediatric and Adolescent Medicine. Its lead author is Eve R Colson of Yale University School of Medicine.

The NICHD launched the Back to Sleep campaign in 1994. The campaign urges parents and caregivers to place infants to sleep on their backs. Since the campaign began, the prevalence of babies being placed for sleep on their backs has increased from roughly 25 per cent to roughly 70 per cent. Corresponding with the increase in back sleeping, the SIDS rate has decreased by more than 50 percent.

To conduct the study, the scientists analyzed data from 1993 to 2007, obtained from the National Infant Sleep Position Study, an annual national phone survey. They found that the proportion of babies placed to sleep on their backs steadily increased between 1993 and 2001 but did not change after 2001.

The survey asked nighttime caregivers (mostly mothers): "Do you have a position you usually place your baby in?"

The researchers found that families who placed their infants on their backs were unlikely to say that they were concerned about their baby choking, or were unlikely to say that they were concerned that their baby would be uncomfortable on their back. These families also were likely to report that their doctor recommended back placement as the sole sleep position.

Conversely, caregivers who were concerned about infant choking, about infant comfort, and who had not received a recommendation for back-only placement from their physician were less likely to indicate that they had placed their infants to sleep on their backs.

The researchers also reported that African-American infants are placed to sleep on their backs less often than whites or Hispanics. The researchers showed that maternal attitudes about issues such as comfort and choking, and doctor recommendation for back sleeping contributed to much of the disparity in back placement between African-Americans and other groups.

A greater proportion of African-American infants than white or Hispanic infants die from SIDS each year.

The researchers concluded that reducing overall SIDS death rates depends on making sure families get back-sleeping advice from their physicians, and addressing concerns about choking and comfort.

Dr Willinger noted that Back to Sleep Campaign materials address concerns about choking. She added that the campaign, which has a continuing education program for nurses, is in the final stages of preparation of a similar programme for pharmacists, who often serve to reinforce health advice in many communities.

Similarly, the campaign will continue its work with practitioner groups to urge all health care professionals who come in contact with newborn infants to urge caregivers to place infants to sleep on their backs. In the study, the researchers reported that between 2003-2007, only 53.6 per cent reported that their doctors had advised them to put their babies on their backs only.

Dr Willinger explained that some caregivers may choose not to place infants on their backs for sleep because of concern that the infants might sleep less soundly. She added that if infants are consistently placed on their backs for sleep, they should become accustomed to sleeping in that position.

Recent studies have shown that infants placed on their sides were more likely to roll on to their stomachs and the current recommendation is for caregivers to place infants to sleep exclusively on their backs. Before this was discovered, however, the initial recommendation was that infants be placed on their backs or sides to sleep.

"Some health professionals may not be aware of the change," Dr Willinger said. "We're continuing our efforts to make sure that they know -- and know to tell their patients -- that infants sleep safest on their backs."

"We know that it is really important for health care providers to tell families that they should place their infants on the back to sleep," said the study's lead author, Dr Colson. "We can't equivocate, or the message gets lost. And we need to serve as role models, placing infants to sleep on their backs, beginning the minute infants are born in our hospital nurseries and paediatric units."

In addition to Dr Colson, other authors of the study were Denis Rybin, Theodore Colton and Michael J Corwin of Boston University; Lauren Smith, of the Massachusetts Department of Public Health; and George Lister, of University of Texas Southwestern Medical Center at Dallas.

The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation.