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SIDS Facts

Sudden Infant Death Syndrome

Sudden Infant Death Syndrome (SIDS) is the diagnosis given for the sudden death of an infant under one year of age that remains unexplained after a complete investigation, which includes an autopsy, examination of the death scene, and review of the symptoms or illnesses the infant had prior to dying and any other pertinent medical history.

SIDS is the leading cause of death in infants between 1 month and 1 year of age. African American children are two to three times more likely than white babies to die of SIDS, and Native American babies are about three times more susceptible. Also, more boys are SIDS victims than girls.

What Are the Risk Factors for SIDS?
A number of factors seem to put a baby at higher risk of dying of SIDS. Babies who sleep on their stomachs are more likely to die of SIDS than those who sleep on their backs. Mothers who smoke during pregnancy are three times more likely to have a SIDS baby, and exposure to passive smoke from smoking by mothers, fathers, and others in the household after pregnancy doubles a baby's risk of SIDS. Other risk factors include mothers who are less than 20 years old at the time of their first pregnancy, babies of mothers who had no or late prenatal care, and premature or low birth weight babies.

What Causes SIDS?
Mounting evidence suggests that some SIDS babies are born with brain abnormalities that make them vulnerable to sudden death during infancy. Studies of SIDS victims reveal that many SIDS infants have abnormalities in the "arcuate nucleus," a portion of the brain that is involved in controlling breathing and waking during sleep. Babies born with defects in other portions of the brain or body may also be more prone to a sudden death. These abnormalities may stem from prenatal exposure to a toxic substance, or lack of a vital compound in the prenatal environment, such as sufficient oxygen. Cigarette smoking during pregnancy, for example, can reduce the amount of oxygen the fetus receives.

Scientists believe that the abnormalities that are present at birth may not be sufficient to cause death. Other possibly important events occur after birth such as lack of oxygen, excessive carbon dioxide intake, overheating or an infection. For example, many babies experience a lack of oxygen and excessive carbon dioxide levels when they have respiratory infections that hamper breathing, or they rebreathe exhaled air trapped in underlying bedding when they sleep on their stomachs. Normally, infants sense such inadequate air intake, and the brain triggers the babies to wake from sleep and cry, and changes their heartbeat or breathing patterns to compensate for the insufficient oxygen and excess carbon dioxide. A baby with a flawed arcuate nucleus, however, might lack this protective mechanism and succumb to SIDS. Such a scenario might explain why babies who sleep on their stomachs are more susceptible to SIDS, and why a disproportionately large number of SIDS babies have been reported to have respiratory infections prior to their deaths. Infections as a trigger for sudden infant death may explain why more SIDS cases occur during the colder months of the year, when respiratory and intestinal infections are more common.

The numbers of cells and proteins generated by the immune system of some SIDS babies have been reported to be higher than normal. Some of these proteins can interact with the brain to alter heart rate and breathing during sleep, or can put the baby into a deep sleep. Such effects might be strong enough to cause the baby's death, particularly if the baby has an underlying brain defect.

Some babies who die suddenly may be born with a metabolic disorder. One such disorder is medium chain acylCoA dehydrogenase deficiency, which prevents the infant from properly processing fatty acids. A build-up of these acid metabolites could eventually lead to a rapid and fatal disruption in breathing and heart functioning. If there is a family history of this disorder or childhood death of unknown cause, genetic screening of the parents by a blood test can determine if they are carriers of this disorder. If one or both parents is found to be a carrier, the baby can be tested soon after birth.

Prepared by National Institute of Child Health and Human Development
Public Information and Communications Branch

How Many Babies Die From SIDS?
According to the Center for Health Statistics (NCHS), each year from 1983 to 1991, the number of SIDS deaths reported in the United States ranged from 5,000 to 6,000. In April of 1992, the American Academy of Pediatrics announced that healthy infants should sleep on their back to reduce the risk of SIDS. Beginning that year, SIDS deaths began to decline somewhat, to 4,890. In June of 1994, the Back to Sleep campaign began, and SIDS deaths declined even more. This decline continued throughout the 1990s, and, according to the NCHS, final figures for SIDS deaths in 1999 were approximately half of what they were in 1991 (2,648 versus 5,349).

When considering the overall number of live births each year in the United States, SIDS remains the leading cause of death in infants between 1 month and 1 year of age, and the third leading cause of death in infants birth to 1 year of age, behind congenital abnormalities and short gestation/low birth weight.
(National Vital Statistics Report, June 26, 2001)

How Do Professionals Diagnose SIDS?
Often the cause of an infant death can be determined only through a process of collecting information, conducting sometimes complex forensic tests and procedures, and talking with parents and physicians. When a death is sudden and unexplained, investigators, including medical examiners and coroners, use the special expertise of forensic medicine (application of medical knowledge to legal issues). SIDS is no exception.

Health professionals make use of three avenues of investigation in determining a SIDS death: the autopsy; death scene investigation; and review of victim and family case history.

The Autopsy
The autopsy provides anatomical evidence through microscopic examination of tissue samples and vital organs. An autopsy is important because SIDS is a diagnosis of exclusion. A definitive diagnosis cannot be made without a thorough postmortem examination that fails to point to any other possible cause of death. Also, if a cause of SIDS is ever to be uncovered, scientists will most likely detect that cause through evidence gathered from a thorough pathological examination.

A Thorough Death Scene Investigation
A thorough death scene investigation involves interviewing the parents, other caregivers, and family members; collecting items from the death scene; and evaluating that information. Although painful for the family, a detailed scene investigation may shed light on the cause, sometimes revealing a recognizable and possibly preventable cause of death.

Review of the Victim and Family Case History
A comprehensive history of the infant and family is especially critical to determine a SIDS death. Often, a careful review of documented and anecdotal information about the victim's or family's history of previous illnesses, accidents, or behaviors may further corroborate what is detected in the autopsy or death scene investigation.

Investigators should be sensitive and understand that the family may view this process as an intrusion, even a violation of their grief. It should be noted that, although stressful, a careful investigation that reveals no preventable cause of death may actually be a means of giving solace to a grieving family.

What SIDS Is and What SIDS Is Not

SIDS Is: