Sudden Infant Death Syndrome (SIDS)

What is Sudden Infant Death Syndrome (SIDS)?

Sudden infant death syndrome (also known as SIDS) is defined as the sudden death of an infant younger than 1 year of age. If the child's death remains unexplained after a formal investigation into the circumstances of the death (including performance of a complete autopsy, examination of the death scene, and review of the clinical history), the death is then attributed to SIDS. Sudden infant death is a tragic event for any parent or caregiver.

  • SIDS is suspected when a previously healthy infant, usually younger than 6 months of age, is found dead in bed. In most cases, no sign of distress is identifiable. The baby typically feeds normally prior to being placed in bed to sleep. The infant is then discovered lifeless, without pulse or respiration. Cardiopulmonary resuscitation (CPR) may be initiated at the scene, but evidence shows a lack of beneficial effect from CPR. The cause of death remains unknown despite a careful review of the medical history, scene investigation, X-rays, and autopsy.
    • SIDS is rare during the first month of life. Risk peaks in infants 2-4 months of age and then declines.
    • Most SIDS deaths occur in infants younger than 6 months of age.

  • Even though the specific cause (or causes) of SIDS remains unknown, scientific efforts have eliminated several previously held theories. We now know the following about SIDS:
    • Apnea (cessation of breathing) of prematurity and apnea of infancy are felt to be clinical conditions that are distinct from SIDS. Infants with apnea may be managed with electronic monitors prescribed by doctors that track heart rate and respiratory activity. Apnea monitors will not prevent SIDS.
    • SIDS is not predictable or preventable.
    • Infants may experience episodes termed apparent life-threatening events (ALTEs). These are clinical events in which young infants may experience abrupt changes in breathing, color, or muscle tone. Common causes of ALTEs include viral respiratory infection (RSV), gastroesophageal reflux disease, or seizure. However, no definite scientific evidence links ALTEs as events that may lead to SIDS.
    • SIDS is not caused by immunizations or bad parenting.
    • SIDS is not contagious or hereditary.
    • SIDS is not anyone's fault.

SIDS Causes

The cause (or causes) of SIDS is still unknown. Despite the dramatic decrease in the incidence of SIDS in the United States in recent years, SIDS remains one of the leading causes of death during infancy beyond the first 30 days after birth. It is generally accepted that SIDS may be a reflection of multiple interacting factors.

  • Infant development: A leading hypothesis is that SIDS may reflect a delay in the development of nerve cells within the brain that are critical to normal heart and lung function. Research examinations of the brain stems of infants who died with a diagnosis of SIDS have revealed a developmental delay in formation and function of several serotonin-binding nerve pathways within the brain (serotonin is an example of a brain chemical known as a neurotransmitter that is important for brain function). These pathways are thought to be crucial to regulating breathing, heart rate, and blood pressure responses.
    • The hypothesis is that certain infants, for reasons yet to be determined, may experience abnormal or delayed development of specific, critical areas of their brain. This could negatively affect the function and connectivity to regions regulating arousal.
    • Arousal, in this context, refers to an infant's ability to awaken and/or respond to a variety of physiological stimuli. For example, a child sleeping facedown may move his or her face into such a position so that the nose and mouth are completely obstructed. This may alter the levels of oxygen or carbon dioxide in the infant's blood. Normally, these changes would trigger arousal responses, prompting the infant to move his or her head to the side to alleviate this obstruction.
    • In addition, other normally protective responses to stressful stimuli may be defective in infants who are vulnerable to SIDS. One such reflex is the laryngeal chemoreflex. This reflex results in changes in breathing, heart rate, and blood pressure when portions of the airway are stimulated by fluids like saliva or regurgitated stomach contents. Having saliva in the airway may activate this reflex, and swallowing may be important to keep the airway clear. When an infant is in the facedown position, the rate of swallowing is decreased. Protective arousal responses to these laryngeal reflexes are also diminished in active sleep in the facedown position.

  • Rebreathing asphyxia: When a baby is facedown, air movement around the mouth may be impaired. This can cause the baby to re-breathe carbon dioxide that the baby has just exhaled. Soft bedding and gas-trapping objects, such as blankets, comforters, water beds, and soft mattresses, are other types of sleep surfaces that may impair normal air movement around the baby's mouth and nose when positioned facedown.

  • Hyperthermia (increased temperature): Overdressing, using excessive coverings, or increasing the air temperature may lead to an increased metabolic rate in these infants and eventual loss of breathing control. However, it is unclear whether the increased temperature is an independent factor or if it is just a reflection of the use of more clothing or blankets that may act as objects obstructing the airway.

Exams and Tests for Sudden Infant Death Syndrome

SIDS is a diagnosis of exclusion, meaning that other causes of death must be ruled out. The cause of an infant's death can be determined only through a process of collecting information and conducting sometimes-complex forensic tests and procedures. All other recognizable causes of death are investigated prior to making the diagnosis of SIDS.

Four major avenues of investigation aid in the determination of a SIDS death: postmortem lab tests, autopsy, death-scene investigation, and the review of victim and family case history.

  • Postmortem laboratory tests are done to rule out other causes of death (for example, electrolytes are checked to rule out dehydration and electrolyte imbalance; cultures are obtained to evaluate whether an infection was present). In SIDS, these laboratory tests are generally not revealing.
  • An autopsy provides clues as to the cause of death. In some sudden, unexpected infant deaths, specific abnormalities of the brain or central nervous system, the heart or lungs, or infection may be identified as the cause of death. The autopsy findings in SIDS victims are typically subtle and yield only supportive, rather than conclusive, findings to explain SIDS.
  • A thorough investigation of the death scene consists of interviewing the parents, other caregivers, and family members, collecting items from the death scene, and evaluating that information. A detailed scene investigation may reveal a recognizable and possibly preventable cause of death.
    • A parent or caregiver may be asked these questions:
      • Where was the baby discovered?
      • What position was the baby in?
      • When was the baby last checked? Last fed?
      • How was the baby sleeping?
      • Where there any recent signs of illness?
      • Was the infant taking any medication, either prescription or over the counter?
  • You should let your doctor know about any family or infant medical history. It is important to note that family history would include any previous history of unexplained infant death, sudden cardiac death, or metabolic or genetic disorders, for example.

Clinical Features of SIDS

Sudden infant death syndrome remains an unpredictable, unpreventable, and largely inexplicable tragedy. The baby is seemingly healthy without any sign of distress or significant illness prior to the incident.

  • Death occurs rapidly while the infant is sleeping.

  • Typically, it is a silent event. The baby does not cry.

  • The infant usually appears to be well developed, well nourished, and is generally felt to be in good health prior to death. Minor upper respiratory or gastrointestinal symptoms are not uncommon in the last two weeks preceding SIDS.

When to Seek Medical Care

Finding an infant pulseless and not breathing is an emergency. Call 911, and begin basic infant CPR.

Management of SIDS

Self-care at home

There is no home care for SIDS. Call 911 for emergency medical services. However, if any of the parents, caregivers, or bystanders has been instructed in infant CPR, they should perform CPR prior to paramedic arrival.

Medical responses

The initial response is directed by the emergency personnel at the scene according to pediatric advanced life support protocols. Resuscitation measures may be implemented unless signs of death are obvious. Initial responses may include the following:

  • Assessment of the infant's airway, breathing, pulse, and blood sugar level
  • Placement of a tube into the trachea to maximize oxygen delivery
  • Emergency responders may establish IV access; medications to restore heartbeat may be given according to advanced life-support protocols.

Can SIDS be Prevented?

There is currently no way to predict which infants are at risk for SIDS. SIDS has been linked to certain risk factors. Therefore, eliminating or preventing these factors has reduced the risk of SIDS for many infants.

  • Sleep position and the local sleep environment: Educate babysitters, day-care providers, grandparents, and everyone who cares for your baby about SIDS risk and the importance of observing the advice offered in the "Back to Sleep" campaign.
    • Back to sleep: You should place your baby on his or her back to sleep at night and nap time.
      • You should avoid fluffy, loose bedding in your baby's sleep area.
      • Keep your baby's face clear of coverings.
      • Be careful not to overheat your baby by overdressing or adding unnecessary covers.
      • Don't allow anyone to smoke around your baby.
      • Use a firm mattress in a safety-approved crib. Avoid the use of infant positioning devices.
      • Do not allow your baby to sleep alongside another person. The risk of unintentional smothering is too great.
      • Keep all "well-child" appointments with your health-care provider, including immunizations.

  • Home monitoring: The use of home cardiorespiratory monitoring for infants perceived to be at risk of SIDS is still controversial. Doctor-prescribed monitors are available that sound an alarm if the baby's breathing or heartbeat stops. The transthoracic electrical impedance monitors are by far the most frequently used and have the widest availability in the United States. These documenting event monitors detect the respiration and heart activity by using three electrodes. In case of breathing irregularities or decreased heart activity, the device gives off an audible and/or visual alarm. The choice of electronic monitor may measure heart rate, respiratory rate, and pulse oximetry (blood oxygen saturation), or any combination of these three parameters. The information recorded should be downloaded periodically and examined by a doctor.
    • Current studies still echo the National Institutes of Health Consensus Report on SIDS. To date, no reports scientifically demonstrate the effectiveness of home monitoring for siblings of SIDS victims (babies born after a family has had a child die of SIDS).
    • Currently, certain guidelines exist for use of home cardiorespiratory monitoring:
      • Infants with one or more life-threatening episodes in which the baby turned blue or became limp requiring mouth-to-mouth resuscitation or vigorous stimulation
      • Symptomatic preterm infants with apnea of prematurity
      • Infants with certain diseases or conditions that include central breathing irregularities
      • If families have questions related to the use of home monitors, they should seek assistance from their child's primary medical-care provider.

  • Motor development: Recent studies have evaluated the effect of back sleeping on an infant's motor development. Babies younger than 1 year of age who slept on their backs showed slightly decreased upper trunk strength as reflected in mild delays in their ability to crawl, sit upright unassisted, or pull to stand.
    • However, it is important to emphasize that face-up sleepers still attained these milestones within the accepted time range for normal development. No significant difference in gross motor development was seen by the time either infant group started to walk.
    • Parents should incorporate a certain amount of tummy time while the infant is awake and observed. This type of play while baby is on his or her tummy is recommended for developmental reasons and may also help to prevent flat spots (plagiocephaly) from developing or persisting on the back of the head.

Outlook (Prognosis) for Families of SIDS Victims

Most counties throughout the United States have access to support services for families following a SIDS death. Each family's grief is unique. However, many families who have experienced SIDS have found it helpful to use the counseling resources that may be provided through public-health nursing agencies, local coroner, or medical examiner offices, or information and counseling programs based at many children's hospitals across the country. Assistance with identifying these counseling programs is provided at the Association of SIDS and Infant Mortality Programs web site.

Support Groups and Counseling for Families of SIDS Victims

Losing a child is a unique crisis for any family, especially when the child has died suddenly, unexpectedly, and for no apparent reason.

  • Do not blame yourselves! Losing a child to SIDS is not your fault.
  • There are no signs or symptoms that you could have recognized and prevented.
  • Grieving is a normal process when dealing with the loss of a loved one. Family, friends, neighbors, workplace, or faith communities may all serve as sources of support. It is important to remember that you are not alone. There are formal support groups and counseling programs available to help you cope with your loss. For further information, you may contact these groups:
  • Association of SIDS and Infant Mortality Programs (a national network of SIDS support groups)

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Medically reviewed by Margaret Walsh, MD; American Board of Pediatrics


Carolan, Patrick. "Sudden Infant Death Syndrome." Oct. 1, 2009. <>.