Sudden infant death syndrome (SIDS) is the unexpected death of an infant under 1 year of age for which no pathologic cause can be determined by an examination of the death scene, an autopsy, and a review of the infant’s medical history. SIDS is a type of sudden unexpected infant death, a term that encompasses all unexpected infant deaths, both deaths from SIDS and those for which a cause is ultimately determined.1 Of the 3500 U.S. yearly cases of sudden unexpected infant death, 27% to 43% are due to SIDS.2,3 A number of other terms are used in pediatrics to refer to sudden and unexpected death. Sudden unexpected death of an infant is interchangeable with sudden unexpected infant death, and sudden death in the young (SDY) refers to such a death in any child ≤19 years old. Sudden unexplained early neonatal death is limited to infants succumbing within the first week of life and is often caused by congenital abnormalities. Sudden intrauterine unexpected death syndrome refers to stillbirths for which a postmortem exam cannot identify a cause, and sudden unexpected death in epilepsy is an unexpected death in an individual with epilepsy (excluding trauma or drowning) in which a postmortem exam does not reveal an anatomic or toxicologic cause.
EPIDEMIOLOGY AND RISK FACTORS
SIDS is the leading cause of death for infants between 1 month and 1 year of age. SIDS rates have declined considerably from 130.3 deaths per 100,000 live births in 1990 to 38.7 deaths per 100,000 live births in 2014.2 This significant decrease can largely be attributed to the safer sleep practices promoted by the American Academy of Pediatrics’ “Back to Sleep” and “Safe to Sleep” campaigns and, to a lesser extent, classifying deaths due to asphyxiation or strangulation in sleep separately from SIDS.4 The incidence of SIDS peaks between 2 and 4 months of age, and boys account for 60% of SIDS deaths.5 There are a disproportionate number of SIDS deaths in lower socioeconomic groups, although this is true for deaths in infancy from all causes. Other risk factors include low birth weight and prematurity.6 There is ethnic variation, with Asian Americans at lower risk and African Americans and Native Americans at higher risk. Mothers of SIDS victims are more commonly <20 years old, overweight, unwed, use drugs, and have made few prenatal and postpartum visits. Prenatal and postnatal maternal smoking increases the incidence of SIDS. SIDS is more likely to occur during the winter months and while the infant is asleep. Thirty percent to 50% of SIDS patients have some acute infection, usually an upper respiratory tract infection, at the time of the event.
Sleep position has received a great deal of attention as a modifiable SIDS risk factor. The prone sleep position is associated with an odds ratio of 4.92 for SIDS. In clinical trials, prone infants were found to rebreathe expired air and experience hypercarbia.7 In addition, infants normally dissipate heat through their head, and prone sleeping may inhibit heat loss, thereby exacerbating hyperthermia, another noted risk factor for SIDS.8 A disproportionate number of infants succumb to SIDS while with a babysitter.9 Many of these infants are found in the prone position. For some infants, this is the ...