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Sudden Infant Death Syndrome

Sudden infant death syndrome (SIDS), a medical mystery of early infancy, is the leading cause of death among apparently healthy infants ages 1 month to 1 year. Most deaths occur between 1 and 4 months of age. The syndrome, also called crib death, occurs at the rate of 2 in every 1,000 live births. Each year in the United States, about 7,000 infants die of SIDS. Although the syndrome was known in ancient times, its cause remains obscure.

The incidence declines rapidly between ages 4 and 12 months. About 60% of victims are male infants who die in their sleep, without warning, sound, or struggle. The incidence is slightly higher in preterm infants, Inuit infants, disadvantaged black infants, infants of mothers under age 20, and infants of multiple births.

Cultural Tip Incidence of SIDS is 2 to 3 times more likely in black children than in white children. Native American children are 5 times more susceptible than white children. Incidence is 10 times higher in SIDS siblings than in children without SIDS siblings. The occurrence of SIDS is slightly higher in infants whose mothers smoke than in children of mothers who don't smoke. It's up to 10 times more common in infants whose mothers are drug addicts than in children of non-drug-addicted mothers.

Infants most commonly succumb to SIDS in the fall and winter. Many have a history of respiratory tract infections, suggesting viral infection as a cause. Studies show conflicting data about abnormal hepatic or pancreatic function. Although the link between apneic episodes and SIDS remains unclear, about 60% of infants with near-miss respiratory events have second episodes of apnea. Some succumb to apnea.


At one time, SIDS was attributed to abuse or accidental suffocation during sleep. On postmortem examination, some SIDS-diagnosed infants show changes indicating chronic hypoxia, hypoxemia, and large-airway obstruction, leading researchers to suspect more than one cause.

Two leading hypotheses are the hypoxemia theory and the apnea theory. The hypoxemia theory suggests that SIDS occurs because of damage to the respiratory control center in the brain from chronic hypoxemia. The apnea theory holds that the SIDS victim experiences prolonged periods of sleep apnea and eventually dies during an episode.

Another proposed cause involves Clostridium botulinum toxin, which has been linked to a few SIDS deaths. A disproved theory is an association between SIDS and diphtheria, tetanus, and pertussis vaccines. Bottle-feeding and advanced parental age don't cause the syndrome, although breast-fed infants are at decreased risk for SIDS.

Signs and Symptoms

In general, the babies appear to die peacefully in their sleep without distress or previous warning symptoms. Occasionally, babies are found blue and not breathing - although if they are close to death they can be successfully resuscitated.

Diagnostic tests

Diagnosis of SIDS requires an autopsy to rule out other causes of death. Characteristic histologic findings on autopsy include small or normal adrenal glands and petechiae over the visceral surfaces of the pleura, within the thymus (which is enlarged), and in the epicardium. Autopsy also reveals well-preserved lymphoid structures; signs of chronic hypoxemia such as increased pulmonary artery smooth muscle; edematous, congestive lungs fully expanded; liquid (not clotted) blood in the heart; and stomach curd inside the trachea.


Because most infants can't be resuscitated, treatment focuses on emotional support for the family. Any infant found apneic and successfully resuscitated, as well as any infant who has a sibling with apnea, may be at risk for SIDS. In such instances, a home apnea monitor may be recommended until the at-risk infant passes the age of vulnerability.

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