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Sudden infant death syndrome

Sudden infant death syndrome (SIDS) is any sudden and unexplained death of an apparently healthy infant aged one month to one year. The term cot death is sometimes used in the United Kingdom, and crib death in the United States. more...

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SIDS is a definition of exclusion and only applies to an infant whose death remains unexplained after the performance of an adequate postmortem investigation including (1) an autopsy, (2) investigation of the scene and circumstances of the death and (3) exploration of the medical history of the infant and family. Generally, but not always, the infant is found dead after having been put to sleep and exhibits no signs of having suffered.

The inexplicability of the death often leaves parents with a deep sense of guilt in addition to their grief.


SIDS is responsible for roughly 50 deaths per 100,000 births in the US. It is responsible for far fewer deaths than congenital disorders and disorders related to short gestation; though it becomes the leading cause of death in otherwise healthy babies after one month of age.

The frequency of SIDS appears to be a strong function of the age, race, education, and socio-economic status of the parents.

Risk factors

Very little is known about the possible causes of SIDS; there is no method for absolute prevention. However, several risk factors are associated with increased probability of the syndrome.

Prenatal risks

  • inadequate prenatal care
  • inadequate prenatal nutrition
  • tobacco smoking
  • use of cocaine or heroin
  • teenage pregnancy
  • less than a one year interval between subsequent births

Post-natal risks

  • low birth weight (especially less than 1.5 kg)
  • exposure to tobacco smoke
  • laying an infant to sleep on his or her stomach (see positional plagiocephaly)
  • failure to breastfeed
  • excess clothing and overheating
  • excess bedding, soft sleep surface and stuffed animals
  • sex (60% of deaths occur in males)
  • age (incidence is higher between 2-4 months)

In addition, research indicates a reduced risk of SIDS in conjunction with a safe co-sleeping arrangement. Though findings are still preliminary, the proximity of a parent's respiration is thought to stimulate proper respiratory development in the infant.

(The use of baby monitors, particularly those with motion sensors, can allow the parents to remotely keep track of their child.)

SIDS and child abuse

Controversial British pediatrician Roy Meadow believes that many cases diagnosed as SIDS are really the result of child abuse on the part of a parent suffering from Munchausen Syndrome by Proxy (a condition which he himself identified). During the 1990s and early 2000s, a great many mothers of multiple apparent SIDS victims were convicted of murder on the basis of Meadow's opinion. However, in 2003 a number of high-profile acquittals brought Sir Roy's theories into disrepute, and many now doubt their credibility. Several hundred murder convictions are now under review.


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Sudden infant death syndrome
From Gale Encyclopedia of Medicine, 4/6/01 by Teresa G. Norris


Sudden infant death syndrome (SIDS) is the unexplained death without warning of an apparently healthy infant, usually during sleep.


Also known as crib death, SIDS has baffled physicians and parents for years. In the 1990s, advances have been made in preventing the occurrence of SIDS, which killed more than 4,800 babies in 1992 and 3,279 infants in 1995. Education programs aimed at encouraging parents and caregivers to place babies on their backs and sides when putting them to bed have helped contribute to a lower mortality rate from SIDS.

In the United States, SIDS strikes one or two infants in every thousand, making it the leading cause of death in newborns. It accounts for about 10% of deaths occurring during the first year of life. SIDS most commonly affects babies between the ages of two months and six months; it almost never strikes infants younger than two weeks of age or older than eight months. Most SIDS deaths occur between midnight and 8 A.M.

Causes & symptoms

Risk factors for SIDS

The exact causes of SIDS are still unknown, although studies have shown that many of the infants had recently been under a doctor's care for a cold or other illness of the upper respiratory tract. Most SIDS deaths occur during the winter and early spring, which are the peak times for respiratory infections. The most common risk factors for SIDS include:

  • Sleeping on the stomach (in the prone position).
  • Mother who smokes during pregnancy. Smokers are as much as three times more likely than nonsmokers to have a SIDS baby.
  • The presence of passive smoke in the household.
  • Male sex. The male/female ratio in SIDS deaths is 3:2.
  • Belonging to an economically deprived or minority family.
  • Mother under 20 years of age at pregnancy.
  • Mother who abuses drugs.
  • Mother with little or no prenatal care.
  • Prematurity or low weight at birth.
  • Family history of SIDS.

Most of these risk factors are associated with significantly higher rates of SIDS; however, none of them are exact enough to be useful in predicting which specific children may die from SIDS.

Theories about SIDS

Medical disorders

As of 1998 it is not known whether the immediate cause of death from SIDS is a heart problem or a sudden interruption of breathing. The most consistent autopsy findings are pinpoint hemorrhages inside the baby's chest and mild inflammation or congestion of the nose, throat, and airway. Some doctors have thought that the children stop breathing because their upper airway gets blocked. Others have suggested that the children have an abnormally high blood level of the chemicals that transmit nerve impulses to the brain, or that there is too much fetal hemoglobin in the blood. A third theory concerns the possibility that SIDS infants have an underlying abnormality in the central nervous system. This suggestion is based on the assumption that normal infants sense when their air supply is inadequate and wake up. Babies with an abnormal nervous system, however, do not have the same alarm mechanism in their brains. Other theories about the cause of death in SIDS include immune system disorders that cause changes in the baby's heart rate and breathing patterns during sleep, or a metabolic disorder that causes a buildup of fatty acids in the baby's system.

Physical surroundings

A recent theory proposes that SIDS is connected to the child's rebreathing of stale air trapped in soft bedding. In addition to the infant's sleeping in the prone position, pillows, sheepskins, and other soft items may contribute to trapping air around the baby's mouth and nose, which causes the baby to breathe in too much carbon dioxide and not enough oxygen. Wrapping a baby too warmly has also been proposed as a factor.


The diagnosis of SIDS is primarily a diagnosis of exclusion. This means that it is given only after other possible causes of the baby's death have been ruled out. Known risk factors aid in the diagnosis. Unlike the pattern in other diseases, however, the diagnosis of SIDS can only be given post-mortem. It is recommended that all infants who die in their sleep receive an autopsy to determine the cause. Autopsies indicate a definite explanation in about 20% of cases of sudden infant death. In addition, an autopsy can often put to rest any doubts the parents may have. Investigation of the location of the death is also useful in determining the child's sleeping position, bedding, room temperature, and similar factors.


There is no treatment for SIDS, only identification of risk factors and preventive measures. The baby's parents may benefit from referral to counseling and support groups for parents of SIDS victims.


SIDS appears to be at least partly preventable, which has been shown by a decrease in the case rate. The following are recommended as preventive measures:

  • Sleep position. The United States Department of Health and Human Services initiated a "Back-to-Sleep" campaign in 1994 to educate the public about sleep position. Prior to that time, an estimated 70% of infants slept on their stomachs, since parents had been taught that a "back down" position contributed to choking during sleep. There are some conditions for which doctors will recommend the prone position, but for normal infants, side or back (supine) positions are better. When placing an infant on his or her side, the parent should pull the child's lower arm forward so that he or she is less likely to roll over onto the stomach. When babies are awake and being observed, they should be placed on their stomachs frequently to aid in the development of the muscles and skills involved in lifting the head. Once a baby can roll over to his or her stomach, he or she has developed to the point where the risk of SIDS is minimal.
  • Good prenatal care. Proper prenatal care can help prevent the abnormalities that put children at higher risk for SIDS. Mothers who do not receive prenatal care are also more likely to have premature and low birth-weight babies. Expectant mothers should also be warned about the risks of smoking, alcohol intake, and drug use during pregnancy.
  • Proper bedding. Studies have shown that soft bedding, such as beanbags, waterbeds and soft mattresses, contributes to SIDS. Babies should sleep on firm mattresses with no soft or fluffy materials underneath or around them-- including quilts, pillows, thick comforters or lambskin. Soft stuffed toys should not be placed in the crib while babies sleep.
  • Room temperature. Although babies should be kept warm, they do not need to be any warmer than is comfortable for the caregiver. An overheated baby is more likely to sleep deeply, perhaps making it more difficult to wake when short of breath. Room temperature and wrapping should keep the baby warm and comfortable but not overheated.
  • Diet. Some studies indicate that breastfed babies are at lower risk for SIDS. It is thought that the mother's milk may provide additional immunity to the infections that can trigger sudden death in infants.
  • Bedsharing with parents. Opinions differ on whether or not bedsharing of infant and mother increases or decreases the risk of SIDS. Bedsharing may encourage breastfeeding or alter sleep patterns, which could lower the risk of SIDS. On the other hand, some studies suggest that bedsharing increases the risk of SIDS. In any case, mothers who choose to bring their babies to bed should observe the following cautions: Soft sleep surfaces, as well as quilts, blankets, comforters or pillows should not be placed under the baby. Parents who sleep with their infants should not smoke around the baby, or use alcohol or other drugs which might make them difficult to arouse. Parents should also be aware that adult beds are not built with the same safety features as infant cribs.
  • Secondhand smoke. It is as important to keep the baby's environment smoke-free during infancy as it was when the mother was pregnant with the baby.
  • Electronic monitoring. Electronic monitors are available for use in the home. These devices sound an alarm for the parents if the child stops breathing. There is no evidence, however, that these monitors prevent SIDS. In 1986, experts consulted by the National Institutes of Health (NIH) recommended monitors only for infants at risk. These infants include those who have had one or more episodes of breath stopping; premature infants with breathing difficulties; and babies with two or more older siblings that died of SIDS. Parents who use monitors should know how to use them properly and what to for the baby if the alarm goes off.
  • Immunizations. There is no evidence that immunizations increase the risk of SIDS. In fact, babies who receive immunizations on schedule are less likely to die of SIDS.

Key Terms

Existing or present at the time of birth.
Crib death
Another name for SIDS.
Lying on the stomach with the face downward.
Lying on the back with the face upward.

Further Reading

For Your Information


  • Kemp, James S., et al. "Softness and Potential to Cause Rebreathing: Differences in Bedding Used by Infants at High and Low Risk for Sudden Infant Death Syndrome." Journal of Pediatrics 132 (February 98): 234-238.


  • Association of SIDS and Infant Mortality Programs. 630 West Fayette Street, Room 5-684. Baltimore, MD 21201. (410)706-5062.
  • National Institute of Child Health and Development/Back to Sleep. 31 Center Drive, MSC2425, Room 2A32, Bethesda, MD 20892-2425. (800)505-CRIB.
  • National SIDS Resource Center. 2070 Chain Bridge Road, Suite 450, Vienna, VA 22181. (703)821-8955.
  • SIDS Alliance. 1314 Bedford Avenue, Suite 210, Baltimore, MD 21208. (800)221-7437.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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