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Sudden infant death syndrome (often known by its abbreviation, SIDS), is the sudden death of an infant under one year of age for which no cause can be found.

Because many SIDS babies die in their cribs, this syndrome has sometimes been called crib death. It is important to emphasize that cribs are not the cause of SIDS.

What is going on in the body?

SIDS is the leading cause of death for babies between the ages of one month to one year. Most SIDS deaths occur between age 2 and 4 months. Most SIDS infants die silently, apparently in their sleep.

The good news is that only about half as many babies die of SIDS today as in the early 1990s and before. The decrease in SIDS is directly related to the campaign to educate parents to place infants on their backs - instead of sides or stomachs - to sleep.

Current research is focused on the "triple-risk model." This theory says that three things must happen at once for SIDS to occur:

• The infant must have an underlying weakness in homeostatic control. Homeostasis involves the vital functions. This includes blood pressure, heart rate, respiration, chemoreception, upper airway reflexes, and body temperature control. The baby's brainstem and nervous system seem to be the key factors in homeostatic control.
• The infant must be in a critical development period for homeostatic control. This critical period is thought to be within the first six months of life, when the baby's body and its systems are still maturing.
• An external stressor has increased the infant's vulnerability to the homeostatic control issues. The most common external stressor appears to be the stomach sleeping position. Other factors may include soft bedding, infection, and fever.

This theory is still being tested, but evidence so far seems to strongly support it. Many studies are going on today, and experts hope to have more answers soon about what causes SIDS and who is at risk for it.

What are the signs and symptoms of the condition?

There are no warning symptoms of SIDS. Often infants have symptoms of an upper respiratory infection, such as a cold, or gastroenteritis in the days before their death. Most infants who die of SIDS appear healthy when put to bed.

What are the causes and risks of the condition?

While there are knownfor SIDS, none of these factors clearly points to a distinctfor SIDS. Many of these factors are also risk factors for the sudden death of infants from other, known causes.

• Age of the child. Most cases occur in infants between one and four months of age. Ninety-five percent of cases occur in infants six months of age or younger.
• Being part of a multiple birth. Twins or triplets are at greater risk for SIDS.
• Being wrapped in blankets during sleep or sleeping on too soft a surface.
• Exposure to tobacco smoke in the baby's environment.
• Having a recent viral illness, such as an upper respiratory infection or gastroenteritis.
• Low APGAR score at birth. The APGAR score is a measure of how well an infant adapts to life outside the womb in the first five minutes after birth.
• Male gender. Boys die of SIDS slightly more often than girls.
• Prematurity. Being born early and having a low birth weight are both risk factors for SIDS.
• Sleeping on the stomach.
• Sharing a crib or bed with another child.
• Sharing a bed with a parent, when parents smoke or have recently consumed alcohol or used drugs.
• Being African American, American Indian, or Alaskan Native. All of these ethnic groups have at least twice the risk for SIDS.

• being unmarried, young, or poor
• having had a large number of pregnancies
• having pregnancies less than 12 months apart
• lack of prenatal care
• smoking during pregnancy
• use of illicit drugs, especially cocaine, during pregnancy
• binge drinking of alcohol during pregnancy

What can be done to prevent the condition?

Because the causes of SIDS are not known, it is hard to tell which specific babies may die of SIDS. Therefore, prevention is aimed at all babies and pregnant women.

THE most important action parents can take to prevent SIDS in their babies is to put them to sleep on their backs, whether at naptime or at night! It's easy to remember this advice with the motto, "Back to Sleep."

Babies sleeping on their sides or stomachs are 2 to 9 times as likely to die of SIDS. Babies who are exposed to smoke in the home have twice the risk of SIDS as babies who live in a smoke-free environment.

Every effort should be made to provide a smoke-free environment, both before the baby is born, and in the home and any day care settings during the early months of life.

Other measures that can help prevent some cases of sudden infant death include the following:

• Avoid putting fluffy blankets, covers, sheepskins, stuffed toys, and pillows in the baby's crib or other sleeping areas.
• Place the baby on a firm mattress, not on a pillow or sofa, to sleep.
• Do not let the baby overheat during sleep. Keep the room warm, but not too warm. The room should be kept at a temperature that feels comfortable to an adult. Too many layers of blankets or clothes can overheat the baby.
• Make sure the baby's face and head stay uncovered during sleep. Tuck the blanket into the crib mattress, with the top of the blanket no higher than the baby's chest.
• Do not put the baby to sleep on a water bed.
• Put the baby on his or her stomach when awake and being watched closely. This can help the baby learn to strengthen shoulder and neck muscles.

During pregnancy, the expectant mother can take the following measures to help prevent SIDS:

• Avoid drugs and alcohol.
• Stop smoking, if she smokes.
• Get good prenatal care throughout the pregnancy. Also, practice a healthy lifestyle, including eating the right food and getting regular exercise.

In addition, the following actions can help maintain the baby's health in general:

• breastfeeding
• regular well-baby checkups with the doctor

Attempts to prevent SIDS through the use of heartbeat and breathing monitors in the home have not been found to be effective and are rarely used.

How is the condition diagnosed?

The diagnosis of SIDS is by an autopsy that rules out other causes for an infant's death. To make the diagnosis of SIDS, the autopsy must be thorough and done by an expert in infant death. The diagnosis of SIDS is made if no other causes of death can be found and the autopsy findings suggest SIDS.

What are the long-term effects of the condition?

SIDS often results in feelings of guilt, sadness, and anger in the parents and other family members.

What are the risks to others?

The risk to others involves the grieving process in those left behind.

What are the treatments for the condition?

There is no treatment for the infant because the diagnosis can be made only after death. Support groups or counseling may be advised for the parents.

What are the side effects of the treatments?

There is no treatment for SIDS and therefore no side effects.

What happens after treatment for the condition?

Parents of an infant who dies of SIDS often go through shock, grief, and guilt. They often feel that there is something they may have done to cause it or could have done to prevent it.

Compassion from friends and family, as well as professionals, can help the parents to cope. Support and empathy are needed. Accusations should be avoided, especially because the parents have already been questioned by law enforcement officials to make sure that the unexplained death was not due to abuse.

While a small percentage of initially unexplained infant deaths are ultimately found to be due to child abuse rather than SIDS, these probably account for less than 5% of cases.

How is the condition monitored?

Any depression or suicidal thoughts in a parent should be reported to the healthcare professional.