TUESDAY, May 3, 2005 (HealthDay News) -- Researchers are puzzling over statistics that show the incidence of sudden infant death syndrome (SIDS) is going down while overall unexpected infant mortality remains mostly unchanged in the United States.
This paradox, seen in numbers from 1992 to 2001, may be the result of some SIDS deaths being reclassified into different categories, such as suffocation or death due to unknown causes, the researchers theorize in the May issue of Pediatrics.
"We wondered, as many other researchers have, why is the SIDS rate going down, but the post-neonatal death rate is not?" said study co-author Dr. Michael Malloy, a professor in the department of pediatrics at the University of Texas Medical Branch in Galveston.
"We started sorting through the various categories for infant deaths," he added, and found that apparent SIDS cases were now being reclassified.
SIDS is the sudden, unexplained death of an infant under 1 year old. It is the leading cause of death for babies between 1 and 12 months old, according to the National Institute of Child Health and Human Development.
Between 1992 and 1999, the SIDS death rate dropped by 55 percent, and the overall infant mortality rate decreased by 27 percent. Most of that decline was attributed to the national "Back to Sleep" campaign, a public education initiative begun in 1992 and designed to make sure infants were put to sleep on their back to reduce the risk of SIDS, according to the study. During that time, the number of infants sleeping on their backs increased from 30 percent in 1992 to 80 percent in 1998.
Malloy said the researchers are in no way "denying the efficacy of the 'back to sleep' program. Supine positioning is a very effective way of reducing the risk for SIDS."
But because the overall sudden unexpected infant death rate then leveled off while the SIDS rate still declined, Malloy said it wasn't clear if the SIDS rate really was dropping.
To answer that question, the researchers went through more than 50 years of national infant mortality data, and concentrated on the most recent data from 1999 through 2001.
In 1999, there were 62 SIDS deaths per 100,000 live births; by 2001, that number was down to 51 per 100,000, they found. In 1999, the overall post-neonatal mortality was 233 deaths per 100,000; in 2001, that number had only dropped to 231.
In the study, the researchers noted that "the concurrent increases in post-neonatal mortality rates for unknown and unspecified causes and suffocation account for 90 percent of the decrease in the SIDS rate between 1999 and 2001."
That observation, they concluded, "suggests that a change in classification may be
occurring."
Laura Reno, director of public affairs for First Candle/SIDS Alliance, said the most difficult part of tracking SIDS cases is that medical examiners and coroners throughout the country aren't consistently using the same types of tests, death scene investigations or death certificate coding. She added that the U.S. Centers for Disease Control and Prevention was trying to enlist local health officials to consistently use the agency's defined protocol.
But, she added, one thing that is clear: "Babies are not dying on their backs in safe cribs."
Along with putting your baby to bed on her back in a crib, Reno also recommended a firm mattress that fits the crib properly and no blankets, crib bumpers, pillows or stuffed toys in the crib.
She said the most important thing parents can do to protect their babies from SIDS is to provide a safe sleep area. It's also important to provide a smoke-free environment, she added, because secondhand smoke exposure is also a risk factor for SIDS.
In a second study in the same issue of Pediatrics, researchers from Belgium suggest that swaddling your baby may also help reduce the incidence of SIDS.
The researchers said that one of the reasons some parents don't put babies to sleep on their backs is that they believe their babies sleep better on their stomachs. However, the researchers found that when babies were swaddled -- wrapped tightly in a sheet or light blanket -- they tended to sleep better, thus offering parents an effective alternative to stomach sleeping.
Reno added a note of caution, however. "When a baby is very young, swaddling might help, but once a baby is moving and very wiggly -- typically between 3 and 5 months -- the swaddling blanket could pose a problem," she said.
More information
The National Institute of Child Health and Human Development offers more information on SIDS and ways to prevent it.
