Sudden infant death syndrome


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.


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


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.

When to call the doctor

Parents or caregivers should immediately call for emergency care if a child is found not breathing or without a pulse or is unable to be aroused from sleep.


In most cases, three techniques are used in an attempt to determine the cause of an infant's death. These are:

  • Death scene investigation. A thorough examination of the scene of death, including recording baby's position, collecting items from the surrounding area, and interviewing family members and/or caregivers, can sometimes point to an external cause of death.
  • Autopsy. The autopsy, usually performed by a medical examiner or coroner, focuses on finding any identifiable cause of death. While parents may reject the idea of an autopsy because they feel it violates their infant's remains, it is often the only tool that can definitively rule out other potential causes of death.
  • Review of family history. Healthcare providers or police interview parents and/or caregivers in order to determine the child's medical and family history, in an attempt to rule out possible illness, child abuse, or other cause of death.


Because SIDS affects seemingly healthy infants, and death is the first symptom of the disorder, it is not possible to treat an infant who is truly affected by SIDS. If life support is implemented and the child is resuscitated, emergency care will be provided in an attempt to stabilize the child. Healthcare personnel perform a complete medical exam and record the child's medical history to exclude other potential causes.


By definition the prognosis for babies affected by SIDS is invariably death. In some rare cases, emergency care providers are able to resuscitate an infant who is seemingly lifeless; the prognosis remains poor in these cases.


In the 1990s a number of countries initiated campaigns aimed at getting parents to put their infants to sleep on their backs or sides. In the United States, the American Academy of Pediatrics (AAP) in 1992 issued an official recommendation that infants be put to bed on their backs (supine position) or on their sides (lateral position). In 1994 the Public Health Service launched its "Back to Sleep" campaign, targeting parents, other care givers, and healthcare personnel with brochures advocating supine or lateral infant sleeping and also including information about other risk factors for SIDS. By the mid-1990s it was apparent that this and similar campaigns worldwide had had a significant—in many cases dramatic—impact in reducing the number of deaths from SIDS. In a number of countries the incidence of SIDS dropped by 50 percent or more. SIDS deaths in Great Britain were reduced by 91 percent between 1989 and 1992; in Denmark they declined by 72 percent between 1991 and 1993; and they were reduced by 45 percent in New Zealand between 1989 and 1992.

In the United States, the AAP recommendations reduced the incidence of front-sleeping in infants from over 70 percent in 1992 to 24 percent in 1996. A decline in SIDS rates, already observed in the 1980s, tripled its previous pace between 1990 and 1994, with SIDS deaths falling 10 to 15 percent between 1992 and 1994. Links between SIDS and other aspects of an infant's sleep environment have also emerged. The best known is the finding that soft, padded sleep surfaces can endanger infants by obstructing breathing or creating air pockets that trap their expelled carbon dioxide, which they can then inhale.

Some research also suggests that co-sleeping (having an infant sleep with the mother in her bed) can help regulate an infant's sleep pattern in ways that reduce the risk of SIDS. (Like supine infant sleeping, co-sleeping is also prevalent among Asian populations, which have a low incidence of SIDS.) Infants who share their mothers' beds become accustomed to frequent minor arousals when the mother shifts position, and their own sleep tends to be lighter and more even than that of infants who sleep alone in their cribs and are more prone to the heavier, but sporadic, breathing that stops and then starts up again with a gasp. Experts speculate that this lighter sleep not only makes it less likely for an infant to stop breathing but also that such an infant, with the "practice" gained from more frequent arousals every night, can be aroused more easily when any respiratory distress does occur. In addition, infants who co-sleep with their mothers are naturally more likely to sleep on their backs or sides, which also reduces the risk of SIDS.

In December 1996 the AAP issued the following updated recommendations regarding infant sleep:

  • Infants should be put to sleep in a nonprone position. The supine position (on their backs) is safest, but sleeping on their sides can also significantly reduce the risk of SIDS. When infants sleep on their sides, the bottom arm should be extended to prevent them from rolling over on to their stomachs.
  • Soft sleeping surfaces should be avoided, and a sleeping infant should not be placed on soft objects such as pillows or quilts.
  • It may be better for parents, with the guidance of their pediatrician, to depart from these recommendations in the case of infants with certain health problems, such as gastroesophageal reflux (GER).
  • Infants should spend some time lying on their stomachs when they are awake and supervised by an adult.

Other precautions parents can take include obtaining adequate prenatal care; avoiding exposing infants to cigarette smoke, either pre- or postnatally; breastfeeding instead of formula feeding; and not allowing an infant to become overheated while sleeping. Another measure taken by some parents is the use of a portable battery-operated monitor that sounds an alarm in response to significant deviations in infants' respiration or heart rates while they are asleep. Monitoring is based on the belief that if parents can quickly reach an infant who has stopped breathing, they can either get him breathing again themselves or call for emergency assistance. There has been no substantiated link between monitoring and the decrease in SIDS, and infants have, in fact, died while being monitored. Nevertheless, monitors provide peace of mind for many parents, especially those who have already lost an infant to SIDS or whose baby has special risk factors for the disorder. Medical opinion is generally in favor of monitoring only for newborns who have had episodes of apnea (cessation of breathing) or for any infant who has had a precipitous, life-threatening interruption of breathing or cardiovascular function.

Parental concerns

Losing a child—a traumatic experience for any parent—is especially difficult for those who lose a child to SIDS because the death is so sudden and its cause can often not be determined. Parents of a child who dies of SIDS do not gain a medical explanation of their infant's death. Although such an understanding does not lessen their loss, it can serve an important function in the healing process, one that SIDS parents do not have. In addition to the emotions that normally accompany grief, such as denial, anger, and guilt, SIDS parents may experience certain other reactions unique to their situation. They may become fearful that another unexpected disaster will strike them or members of their families. After the death of a child from SIDS, parents often become over-protective of the infant's older siblings and of any children born subsequently. Some fear having another child, due to misgivings that the tragedy they have experienced may repeat itself. Parents of children who die of SIDS often make major changes in their lives during the period following the death, such as relocating or changing jobs, as a way to avoid confronting painful memories or as a way to protect themselves against the SIDS death of another baby by changing the circumstances of their lives as much as possible.

SIDS deaths place a great strain on marriages. Parents' individual ways of coping with their grief may prevent them from giving each other the support they need, creating an emotional distance between them. Nevertheless, the divorce rate among SIDS parents appears to be no higher than that for the general population, and in one survey half the respondents reported that their marriages had ultimately been strengthened by the experience.

A SIDS death also has a significant effect on the infant's siblings. Young children often experience developmental regressions in toilet training or other areas. Some fear going to sleep, which they associate with the death of their baby brother or sister. As with any death in the family, children need to be reassured that they are not guilty in any way. Many pose difficult questions to their parents, wanting to know why the baby died or where he has gone, or even whether they are going to die, too. Children may also come to feel jealous of the attention paid to the infant who has died or resentful of the disruption the death has caused in their family's life. Most parents report that their way of caring for their remaining children changes after the family experiences a SIDS death. Having young children (or infants born later on) sleep with them at night makes some parents feel more confident of preventing a second tragedy from occurring. In addition to overprotecting their children and worrying about their health, SIDS parents may also spoil them and find it hard to say no to their requests. On the positive side, many parents simply value their remaining children more, spend more time with them, and become closer to them. In a minority of cases, however, the reverse happens, and parents feel emotionally distant from their surviving children. In addition, fear of being hurt sometimes makes it difficult for some parents to bond with babies born later.

Many parents of infants who die of SIDS are helped by participating in local support groups, where they can share their feelings and experiences with others who have undergone the same experience. Counseling can also be beneficial, especially with a mental health professional experienced in dealing with parental grief.


Apnea —The temporary absence of breathing. Sleep apnea consists of repeated episodes of temporary suspension of breathing during sleep.

Co-sleeping —Having an infant sleep with the mother in her bed.

Gastroesophogeal reflux —Backward flow of stomach contents into the esophagus.



Byard, Roger W., et al. Sudden Infant Death Syndrome: Problems, Progress, and Possibilities. Oxford, UK: Oxford University Press, 2001.

Mawhiney, Robert. S.I.D.S.: New Research into Sudden Infant Death Syndrome—Cause and Effect. Philadelphia: Xlibris Corp., 2003.


Anderson, Robert, and Betty Smith. "Deaths: Leading Causes for 2001." National Vital Statistics Report 52, no. 9 (November 7, 2003): 1–86.


American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007–1098. Web site:

National SIDS/Infant Death Resource Center. 2070 Chain Bridge Rd., Suite 450, Vienna, VA 22182. Web site:

SIDS Alliance. 1314 Bedord Ave., Suite 210, Baltimore, MD 21208. Web site:



National SIDS/Infant Death Resource Center. Available online at (accessed November 4, 2004).

Tabib, Shahram, Thomas Tsou, and Charles Drew. "Sudden Infant Death Syndrome." eMedicine Health , July 22, 2004. Available online at (accessed November 4, 2004).

Stephanie Dionne Sherk

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