A review of scientific literature recently published in JAMA Pediatrics summarizes the state of knowledge about causes and risk factors for Sudden Infant Death Syndrome (SIDS).


Sudden infant death syndrome (SIDS) is the sudden, unexplained death of a child under the age of 1 year old. It generally occurs while the child sleeps (and thus is also known as “crib death”), and typically affects babies who were otherwise apparently healthy.

The causes of SIDS are not clear.  Death as a result of SIDS is usually determined only by process of elimination – when investigation and autopsy have found no other explanations for the child’s death. In the United States, it is the leading cause of death for children between the ages of one month and one year.

While the exact pathology for SIDS is not understood, most sources believe that the syndrome results from a combination of three principal risk factors: (1) an infant with underlying biological susceptibility such as impaired responsiveness to low or no oxygen; (2) a sleeping position or soft bedding that can impede breathing or oxygen intake; and (3) an early development stage (typically, between 2 to 4 months of age) where the infant is unable to extract him/herself from danger.

The identification of these three factors led to the Back to Sleep campaign (now “Safe to Sleep”), which recommends that infants be placed on their backs when put to sleep. Not only does this position present less danger of suffocation from pillows or bedding than other sleeping positions, but studies have also shown that infants lying on their backs have better arousal thresholds than infants on their bellies, and are thus more likely to wake or move if breathing becomes impeded.

Since the implementation of “Back to Sleep” in 1994, SIDS rates have been cut in half. However, rates of other types of deaths, which previously would have been attributed to SIDS, have increased. These include deaths by accidental suffocation and strangulation in bed, as well as other categories of “ill-defined” deaths.

Studies attempting to better understand the mechanisms behind SIDS have identified several potential risk factors:

  • Sleep position – belly sleeping appears to be associated with increased risk of re-breathing expelled air which is high in carbon dioxide and low in oxygen, leading to hypercapnia, hypoxia, and depressed cerebral oxygenation; it may also be associated with overheating, altered autonomic control of the cardiovascular system, and impaired arousal thresholds.
  • Bed-sharing – in one study, bed sharing was suggested to be the highest risk factor for SIDS, likely because of displaced bedding, overheating or rolling on top of the infant. Room-sharing, which still facilitates breastfeeding and allows the parent to monitor the child, is suggested as a safer alternative arrangement.
  • Soft bedding – the use of soft bedding such as blankets, pillows, bumper pads and positioner pads has been associated with 5-fold increase in SIDS, regardless of the infant’s sleep position, and a 21-fold increase when the infant sleeps on his/her belly.
  • Sleep surfaces – Firm, tight-fitting crib mattresses are the safest sleep surfaces for infants. Sofas are one of the most dangerous sleep surfaces.
  • Maternal smoking – both in utero and environmental exposure to smoking have been shown to increase the risk of SIDS. In utero exposure, in particular, may reduce the infant’s lung capacity and causes neurotoxicity, which can impair the infant’s arousal response.
  • Prematurity – Infants born premature or with low birth-weight have a 4 times greater risk of dying from SIDS than full-term babies. The increase in risk is thought to result from an underdeveloped autonomic nervous system, causing impaired arousal response.

On the other hand, other factors are suggested to reduce the risk of SIDS:

  • Breast-feeding – multiple studies indicate that breastfed infants have a lower incidence of SIDS. While protective benefits are highest among exclusively breastfed infants, it appears that any extent of breast milk consumption is beneficial.
  • Pacifier use – recent data suggests that pacifier use reduces the incidence of SIDS, possibly by increasing arousability, increasing sleeping blood pressure, and improving autonomic nervous system control. Falling asleep with a pacifier appears to be beneficial, even if the pacifier falls out after the infant is asleep.

While some studies have suggested that immunization may reduce the risk of SIDS, other studies have rejected this theory. At present, there is not thought to be any association between immunizations and the risk of SIDS.

Overall, the best strategy for reducing the risk of SIDS continues to be ensuring a safe sleeping environment for the infant.




Written By: Linda Jensen

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