Most definitive study of its kind shows that sleeping on the stomach increases infant SIDS risk

Researchers have conducted the most definitive study of its kind to show that sleeping on the stomach increases the risk of U.S. infants for Sudden Infant Death Syndrome (SIDS). Previously, researchers had relied largely on overseas studies for making the recommendation that infants be placed on the back to sleep in order to reduce their risk for SIDS.

The study focused primarily on SIDS cases among African Americans, a group at roughly twice the risk for SIDS than are Caucasians. The findings appear in Pediatrics, October 2002. The research was supported by the National Institute of Child Health and Human Development (NICHD), the National Institute on Deafness and other Communication Disorders, and the Centers for Disease Control and Prevention.

The study results provide strong support for the American Academy of Pediatrics’ 1992 and 1996 recommendations that infants be placed to sleep on their backs to reduce the risk of SIDS. The research also underscores the urgency of current programs to ensure that African Americans receive this recommendation.

“This is the largest, most comprehensive study of SIDS risk in an urban, high-risk setting,” said Duane Alexander, M.D., Director of the NICHD. “Other studies have linked sleeping on the stomach with Sudden Infant Death Syndrome, but the Chicago Infant Mortality Study makes the strongest case to date.”

“Racial and ethnic disparities in infant mortality have been among the most persistent in our society,” said James Marks, M.D., director of CDC’s chronic disease program. “This study suggests that at least some of the disparity can be eliminated by wide use of the supine [back] sleeping position among African-American infants.”

In their study, the researchers used the NICHD definition of SIDS: “the sudden death of an infant under one year of age, which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history.” In all, the researchers examined the records of 260 infants from the ages of birth to one year who had died of SIDS in Chicago, Ill. between November 1993 and April 1996. Of these, 75 percent were African American, 13 percent were white, Hispanic, and another 12 percent were white, non-Hispanic.

The study was conducted in Chicago because that city has a large African American community. The researchers compared information about each infant to information about a control infant–a living infant of comparable age, who was from the same racial and or ethnic group, and who had a similar birth weight. All of the SIDS deaths were evaluated by the Cook County medical examiner’s office; autopsies had been conducted to rule out other causes of death. Death scene investigators conducted interviews about circumstances surrounding the deaths. Roughly two weeks after the death, another interview was conducted with the infant’s primary caregiver. This interview included questions not included on the death scene investigation, such as the infant’s routine sleep patterns and access to health care.

The current study found that African Americans at that time were less likely than Caucasians to have been informed by health care personnel to avoid placing infants to sleep on the stomach. Most of the SIDS deaths occurred within the first four months of life, with most of these occurring between the first month and the third month. Consistent with other studies, most of the SIDS infants had died in the fall or winter–64 percent.

The percentage of stomach sleeping for the infant’s last sleep was similar in all of the SIDS infants–58 percent among African Americans, and 55 percent for all other ethnic groups. Among the control group, 43 percent of African Americans were usually placed to sleep on their stomachs, compared to 12 percent for the other groups. Infants placed to sleep on their stomachs were at more than twice the risk for SIDS as were infants sleeping in other positions.

“Our study highlights the need for health care professionals to inform parents of all racial and ethnic backgrounds about the importance of placing their infants to sleep on their backs,” said the study’s principal investigator, Fern R. Hauck, M.D., M.S., now with the Department of Family Medicine, University of Virginia Health System in Charlottesville.

For the control group, 64 percent of mothers said that a doctor or nurse had advised them after delivery about infant sleeping position. The most common recommendation was that infants be placed to sleep on their sides, consistent with recommendations at that time. The next most common recommendation was that infants be placed to sleep on their stomachs. The study authors theorized that, at the time, many health care professionals feared that infants placed to sleep on their backs might choke on vomit if they happened to spit up during the night. In contrast, only 46 percent of those whose infants had died of SIDS said they had received advice from health care professionals on how to place their infants for sleep. For both the SIDS infants and controls, a greater proportion of African Americans (25 percent) than Caucasians (7 percent) said they had been advised to place their infants to sleep on their stomachs.

In 1992, the American Academy of Pediatrics recommended that infants not be placed to sleep on their stomachs. (The AAP revised this recommendation in 1996, to say that placement on the back is the preferred sleeping position for all healthy infants.) These recommendations were based on studies of infants from New Zealand, Australia, and the United Kingdom. However, few studies had been conducted specifically on whether stomach sleeping increased U.S. infants’ risk for SIDS. The Chicago Infant Mortality Study sought to determine if the stomach sleeping position contributed to SIDS in an urban, African American population at high risk for the condition. The study authors described the 1991 Chicago SIDS rate as “alarmingly high”–2.6 SIDS deaths per 1000 live births, as compared to the overall U.S. rate of 1.3.

The current study is part of a body of research sponsored by the NICHD on infant sleep practices and the causes of SIDS. This large body of research, together with compelling scientific evidence from around the world, confirmed the safety and effectiveness of back sleeping. Based on this evidence, the NICHD formed a coalition of national organizations to launch a national public awareness campaign called Back to Sleep in 1994. Along with NICHD, the coalition consisted of the Health Resources and Services Administration, the American Academy of Pediatrics, the Association of SIDS and Infant Mortality Programs (formerly the Association of SIDS Program Professionals), and the SIDS Alliance. At that time, the SIDS rates for African Americans were double those for Caucasians. (See chart at http://www.nichd.nih.gov/sids/sidsrates.pdf.) Since the start of the NICHD-led campaign in 1994, the SIDS rates for both groups have declined by about 50 percent, but a significant disparity still remains. To help eliminate this disparity, the NICHD joined with the non-profit National Black Child Development Institute in a program to reduce SIDS among African American infants in Chicago and around the country. The Alpha Kappa Alpha sorority, the Women of the NAACP, and the Coalition of 100 Black Women are among the many organizations that have joined in this effort. More information about this outreach program is available on the NICHD Web site at (http://www.nichd.nih.gov/sids).

One of the strengths of the current study is that it used standard criteria for evaluating all potential SIDS deaths, making it easy to compare details among the cases. In prior studies, the SIDS cases sometimes had been evaluated under a number of different standards. Similarly, the researchers conducted an extensive investigation of the death scene that involved asking the infants’ caregivers detailed questions. These included questions about: the events preceding the infant’s death, discovery of the deceased infant, the medical history of the infant and family, as well as maternal alcohol, tobacco, and drug abuse before and during pregnancy.

The study relied primarily on the ability of mothers and family members to recall events regarding the infant’s last sleep. The study authors noted that mothers who had lost their infants to SIDS may have been better able to recall the circumstances surrounding their infant’s last sleep than were the mothers of the control infants. The study authors do not believe this possibility is likely, however, as both cases and controls were interviewed within a short time of their infants’ last sleep period.