Sudden Infant Deaths Decline; but Causes Remain a Mystery

Public health and awareness campaigns inspired by clues from continuing research have reduced Sudden Infant Death Syndrome (SIDS) cases in the US by more than half in the past fifteen years. The cause or causes of SIDS remain largely unexplained, though, and according to a Medical College of Wisconsin expert the mystery of SIDS may remained unsolved for some time to come.

"SIDS is the sudden, unexpected and unexplained death of a baby under one year of age," said William H. Gershan, MD, Medical College Associate Professor of Pediatrics. "It usually occurs during sleep. Babies are put down to sleep and seem fine, and are found dead either later at night or the following morning. Right now there are about 2,000 infant deaths from SIDS in the US per year.

"That number was considerably higher - 4,000 to 5,000 deaths annually - as recently as the late 1980s into the 1990s. The main reason the number of deaths has gone down so much is the 'Back to Sleep' campaign, which started in other countries like Australia, New Zealand, and England. In those countries they found a much lower incidence of SIDS when babies were placed on their backs to sleep.

"In 1992 the American Board of Pediatrics recommended the back position for babies' sleep, and over the past decade-plus it really has become the prevalent position of sleep for babies in this country. Other public education efforts let people know that it's OK for babies to play on their tummies when they're awake because there was some concern about infants spending all of their time on their backs."

Search for Root Causes Continues
A key word in describing SIDS, as opposed for example to clear-cut cases of infant death by suffocation or choking, is "unexplained." When an infant dies during sleep and the specific reason is not explained by known disease, accident or injury, the death is often attributed to SIDS.

According to the National Institutes of Health, SIDS is still the leading cause of death among children between one month and one year of age. Data collected by NIH indicates that most SIDS deaths occur when babies are between two months and four months old.

"There are certainly many ideas about the possible causes of Sudden Infant Death Syndrome," said Dr. Gershan, who practices at the Children's Hospital of Wisconsin Pulmonary Clinic. "One important current hypothesis tells us that a combination of factors may need to be present, although this 'triple risk model' of age combined with a vulnerable infant and an inciting incident doesn't tell us what causes SIDS when it occurs.

"Many people think that SIDS probably involves apnea, where breathing stops during sleep. A major question still unanswered is whether apnea is the actual event that causes the death, or whether the apnea follows another unknown event that causes the baby to stop breathing. Regardless, many experts attribute SIDS to some abnormality in the control of breathing.

"Some newer studies have come out showing subtle abnormalities or chemical changes in the brain stems of some babies who had succumbed to SIDS. There may be hereditary risk that's passed along. That research points to some sort of control of breathing factor in SIDS, but again it's certainly still a bit of a mystery."

Compared to white babies, African-American babies are more than two times more likely to die of SIDS and American Indian/Alaska Native babies are nearly three times more likely to die of SIDS. Dr. Gershan noted that it's not clearly understood why certain populations are at higher risk for SIDS.

Many Risk Factors are Avoidable
"In all populations, the biggest identified risk factor for SIDS was sleeping on the tummy," said Dr. Gershan. "That's still a big factor but quite less common than it used to be. Probably a bigger risk now is when babies who typically sleep on their backs are occasionally put on their tummy, for example for a nap or while staying with a relative for a night. One research project indicates that those babies whose back-sleeping routine is changed could be at a much higher risk for SIDS than even those who always sleep on their tummy.

"Believe it or not, probably the biggest risk factor for SIDS identified by current research is smoking, especially smoking by the mother, now that most babies sleep on their backs. Both smoking while the baby is in the womb and second-hand smoke after birth appear to be risk factors. Babies who are born very prematurely also have a higher rate of SIDS incidents.

"At even higher risk are premature babies with premature lungs and a lot of breathing problems in a chronic lung condition called broncho-pulmonary dysplasia. Another risk factor is placing babies in beds with a lot of blankets or 'cushy' pillows, because one of the possible mechanisms of SIDS is a form of suffocation that takes place when the baby's head is covered or mashed into a very soft pillow or mattress."

Some of the advice offered by Dr. Gershan and NIH on how to reduce SIDS risk is summarized below:

• Place babies on their backs to sleep, even if it's just for a nap, and remind relatives and other temporary caregivers to do so as well.
• Don't place babies in beds or cribs with pillows, a lot of blankets, styrofoam objects or large soft toys in which their heads can be stuck.
• Stop smoking during pregnancy; if you continue to smoke after the baby is born, don't smoke in the home.
• Watch that the temperature in the baby's room is not too warm, there is some evidence that SIDS-related problems arise when babies are overheated.
• Use common sense if you sleep with your baby and avoid letting several siblings sleep in the same bed. Whether 'co-sleeping' is a risk factor for SIDS is still up in the air, said Dr. Gershan, but for a lot of reasons it's probably safer to avoid it.

A Life-Threatening Event Every Week
A case involving an infant that doesn't result in death but is a close call is known as an apparent life-threatening event (ALTE). Dr. Gershan and others at the Medical College, Children's Hospital, and other institutions are conducting continuing research into these occurrences. On average, Children's Hospital alone sees about one such case each week.

"An ALTE is an episode in a baby where the infant either stops breathing or turns blue or limp, or has some altered consciousness, and appears to parents or caregivers to be near death and typically requires some form of resuscitation. Back in the '70s and '80s some in pediatrics called these events 'near-miss SIDS' because they thought they would have been SIDS deaths if the caregivers had not somehow averted them.

"That changed because there was little evidence that these cases would have been SIDS without intervention, so the name was changed to ALTE. We've been looking at these ALTE events and some of the circumstances and demographics behind them, as fact-finding in general and hopefully to also develop a protocol around the identification and medical management of these hospitalized infants.

"Some of these kids are kept in the hospital overnight for observation, in other more severe episodes babies can be in the hospital or intensive care unit for days or even weeks. Just at Children's Hospital, we determined that there have been about 50 babies brought in with an apparent life-threatening event each year for several years.

"The goal of all of this research, not just the ALTE work, is to prevent SIDS, and we've made a lot of progress in the last several years. But there's a ways to go yet. In rough average numbers, there are still 30 to 40 babies who die of SIDS in Wisconsin every year. There isn't a medical 'cure' on the horizon and we can't identify if a particular baby may die of SIDS, so education and prevention by minimizing known risks remain the keys to further reducing the number of deaths."

Dan Ullrich
HealthLink Contributing Writer

This article includes information from the National Institute of Child Health & Human Development.

Dr. Gershan practices at the Children's Hospital of Wisconsin Pulmonary Clinic.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.