Does Swaddling Increase the Risk of SIDS?

Sudden Infant Death Syndrome (SIDS), the unexplained sudden death of an infant under the age of one year, affects approximately 1500 infants annually. Its exact cause remains a mystery, but a recent study in Pediatrics has revealed a possible risk factor. Researchers have found that an infant who is swaddled – wrapped tightly in a blanket or cloth with their limbs restricted – while placed on their front or stomach to sleep faces a higher risk of SIDS.

Thomas Keens, MD, faculty member in the division of Pediatric Pulmonology and Sleep Medicine and director of the Cystic Fibrosis Care Center at Children’s Hospital Los Angeles, spoke to us about the implications of this study. Keens is also Chair of the California SIDS Advisory Committee, which advises the California Department of Public Health on issues related to SIDS.

Is there a hypothesized cause for SIDS?

The cause of SIDS remains unknown.  However, most SIDS researchers believe in the triple risk hypothesis of SIDS.  That is, SIDS is not due to one abnormality in one physiological system.  Rather, researchers now believe it is due to an interaction of three factors. First is the developmental window of vulnerability. SIDS is most common at 2-4 months of age when the cardiorespiratory system of all infants is in rapid transition and therefore unstable. So, all infants in this age range are at risk for dysfunction of neurological control of breathing.

The second factor is environmental challenges, which vary from sleeping in a prone (on the stomach) position and soft bedding to overheating and second hand tobacco exposure. Third, some infants are intrinsically vulnerable and have differing abilities to respond to different stresses.

This hypothesis is supported by recent research out of Harvard University, which has shown the brainstem levels of serotonin – a neurotransmitter important in life support functions in the brain like breathing and heart rate – is decreased in children who died of SIDS. This suggests that in this triple risk hypothesis, those infants who die have increased vulnerability (decreased life support neurotransmitters). In another scenario, not all babies sleeping prone in soft bedding would die, but those who die were probably less able to deal with the environmental challenge of the prone position and soft bedding.  

This remains a hypothesis, but most SIDS researchers believe this combination of multiple factors is the mechanism of death in these babies.

How could swaddling be potentially increasing risk of SIDS?

Prone sleeping is the single most important risk factor for SIDS.  If a baby is swaddled, and placed prone to sleep, that infant has no ability to try to lift or turn his/her head to avoid a potentially dangerous situation where the face is buried in bedding. Even if babies are placed on their backs to sleep, they begin to roll over at ~3-4 months of age, some earlier.  If a swaddled infant rolls from the back to the stomach, he/she cannot move to try and correct the position.  Therefore, the infant will be in the most dangerous position. Suffocation is possible.  If an infant is swaddled with thick blankets, this can lead to overheating, which is another high risk factor for SIDS.  If the infant is swaddled with blankets covering the face, this is yet another risk factor for SIDS.  

Thus, if infants are swaddled, which is often done to encourage sleep, they should always be placed supine and be swaddled in thin blankets to prevent overheating. The face should not be covered, and swaddling should be discontinued when the infant may begin to roll from supine (on the back) to prone, which is at about 3-months. Increasingly, the recommendation by physicians is to stop swaddling when the infant is 2-months of age.

What are some other risk factors for SIDS?

Other risk factors for SIDS (which have been shown to increase risk for but not necessarily cause SIDS) include unsafe bedding (a soft mattress as opposed to a firmer one), having items in the crib with the infant, cigarette smoke exposure, bedsharing (i.e. infants sleeping in the parents’ bed), and overheating.

What SIDS-related research has been conducted here at CHLA?

CHLA has a proud legacy of contributing to SIDS research.  As late as the late 1980’s, many believed that SIDS was due to babies not breathing during sleep (apnea).  We were one of the first to show that recordings of breathing and heart rate did not predict SIDS or serious apneic events in high risk infants.

So, we focused our attention on a different question.  Because infants have an immature respiratory control, all infants have many breathing pauses.  We reasoned that is may not be so important to know why they have apneas, but to understand if and how they can rescue themselves from these pauses.  If an infant has a prolonged breathing pause, he/she could become hypoxic (low oxygen).  So, can these infants rescue themselves from a breathing pause by waking up in response to the low oxygen?  We found that even normal infants seem to be born with an ability to awaken in response to low oxygen, but they lose this at ~2-3 months of age, which is when the incidence of SIDS peaks.  We do not think this is the cause of SIDS, but we think it is one of the factors which makes every infant more vulnerable to SIDS at the peak age of 2-4 months. We also were the first to describe an increased SIDS risk for infants of substance abusing mothers.    

CHLA continues to promote SIDS risk reduction and safe infant sleep education, including promoting a safe infant sleep environment in CHLA.  We have been active in the education of county public health nurses to support families who have experienced the devastating death of an infant from SIDS.

Any additional comments?

My interpretation of this study is that it is not perfect.  There are relatively small numbers of SIDS and controls, but the data obtained differed between studies.  I agree with the authors that this study is not powerful enough to prove that swaddling increases the risk for SIDS.  However, it does reinforce two current recommendations: (1) Swaddled infants should never be placed prone (on the stomach); and (2) if started, swaddling should be stopped at 2-3 months of age when an infant begins to roll over because the danger of a swaddled infant on the stomach who cannot move.

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