Sudden Infant Death Syndrome

Definition

Sudden infant death syndrome (SIDS) is the sudden, unexpected death of a seemingly normal, healthy infant under one year of age that remains unexplained after a thorough postmortem investigation, including an autopsy and a review of the case history.

Description

SIDS is a defined medical disorder that is listed in the International Classification of Diseases, 9th Revision (ICD-9). The first published research about sudden infant death appeared in the mid-nineteenth century. Since then, researchers and healthcare providers have struggled to define the syndrome and determine its causes. The key characteristics of SIDS include:

• infant less than one year of age
• infant seemingly healthy (no preceding symptoms)
• complete investigation fails to find a cause of death
• no associated child abuse or illness

Demographics

In the United States, SIDS was the third leading cause of postneonatal deaths (those occurring between the ages of 28 days and one year) in 2001. According to the National Center for Health Statistics, 2,234 infants in the United States died of SIDS in 2001, or 8.1 percent of total infant deaths. (In the late 1990s, many sources placed the annual total number of deaths as high as 6,000 due to possible under-reporting.) Ninety percent of SIDS deaths occur during the first six months of life, mostly between the ages of two and four months. SIDS also occurs about 1.5 times more frequently in boys than girls. The rate of SIDS in African-American infants is twice as high as that of Caucasians, a fact often attributed to the lower quality of prenatal care received by many African-American mothers.

Causes and symptoms

Studies have identified many risk factors for SIDS, but the actual cause of the disorder remains a mystery. Although investigators are still not sure whether the immediate cause of SIDS deaths is due to respiratory failure or cardiac arrest, patterns of infant sleep, breathing, and arousal are a major focus of research in the early 2000s. It is known that young infants often stop breathing for short periods of time, then gasp and start again. Some researchers and physicians believe that SIDS involves a flaw in the mechanism that is responsible for resumption of breathing.

Aside from its occurrence during sleep, the other most striking feature of SIDS is its narrow age distribution, which has prompted researchers to examine the developmental changes that take place between the ages of two and four months, especially between the ages of two and four months, when most SIDS deaths occur. A growing number of experts believe that rather than a single cause, there are a number of different conditions that can cause or contribute to SIDS. This picture is complicated still further by the interaction of possible physical abnormalities with a number of environmental and developmental factors known to increase the risk of SIDS. Premature infants and low birth weight babies in general are known to be at increased risk of developing SIDS, as are infants born to teenage mothers, poor mothers, and mothers who for any reason have had inadequate prenatal care. Other risk factors include maternal smoking during pregnancy, exposure to smoking in the home after birth, formula feeding rather than breastfeeding, and prior death of a sibling from SIDS (although this is thought to be due to shared environmental risk factors rather than genetic predisposition). Many SIDS deaths occur in babies who have recently had colds (a possible reason that SIDS is most prevalent in winter, the time when upper respiratory infections are most frequent).

As of 2004, the most significant risk factor discovered for SIDS was placing babies to sleep in a prone position (on their stomachs). Studies have reported that anywhere from 28 percent to 52 percent of infants who die of SIDS are found lying face down. Another finding reinforcing the connection between SIDS and prone-sleeping is the fact that SIDS rates are higher in Western cultures, where women have traditionally placed children on their stomachs, than in Eastern ones, where infants usually sleep on their backs. The cause-effect relationship between prone-sleeping and SIDS is not fully understood. However, it is known that when infants sleep on their backs they are more prone to arousal, and SIDS is often thought to involve a failure to rouse from sleep. In addition, prone-sleeping raises a baby's temperature, which is another risk factor for the disorder.

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Author Info: Stephanie Dionne Sherk, Thomson Gale, Gale, Detroit, Gale Encyclopedia of Children's Health, 2006

This feature is for informational purposes only and should not be used to replace the care and information received from your healthcare provider. Please consult a healthcare professional with any health concerns you may have.