Sudden unexpected infant death (SUID) is a term used to describe any unexpected and sudden death in a child less than 1 year of age, which often occurs during sleep or in the infant's sleep area. Common types of SUID include sudden infant death syndrome (SIDS) and accidental suffocation and strangulation in bed.
Sudden unexpected infant death (SUID) is a term to describe a sudden and unexpected death in an infant less than 1 year old, whether explained or unexplained, occurring during infancy. Definitions of the term vary; the Centers for Disease Control and Prevention (CDC) definition includes only deaths in which the cause was not obvious before investigation (1), whereas the American Academy of Pediatrics definition includes both explained and unexplained deaths (2). Almost all SUID cases occur when the infant is thought to be sleeping.
Sudden infant death syndrome (SIDS) is a subset of SUID and is the sudden and unexpected death of an infant or young child between 1 month and 1 year of age in which an examination of the death scene, thorough postmortem examination, and clinical history fail to show cause.
The other subset of SUID includes those sudden and unexpected child deaths where a cause, such as asphyxiation, strangulation, an infection, a metabolic disorder, or any other identified cause, is found.
SIDS is the most common cause of death in infants between 1 month and 1 year of age (3), accounting for 35 to 55% of all deaths in this age group (1). In the United States in 2020, the rate of SUID was 92.9 deaths per 100,000 live births; SIDS was the most common type, with a rate of 38.4 deaths per 100,000 live births (1).
There are racial and ethnic disparities; from 2015 to 2019, rates of SUID were highest in non-Hispanic American Indian/Alaska Natives, non-Hispanic Black people, and non-Hispanic Native Hawaiian/Other Pacific Islanders. Peak incidence is between the second and fourth months of life.
References
1. Centers for Disease Control and Prevention (CDC): Sudden Unexpected Infant Death and Sudden Infant Death Syndrome: Data and Statistics. Accessed 12/13/2022.
2. Moon RY, Carlin RF, Hand I, et al: Sleep-related infant deaths: Updated 2022 recommendations for reducing infant deaths in the sleep environment. Pediatrics 150(1):e2022057990, 2022. doi: 10.1542/peds.2022-057990
3. National Institute of Child Health and Human Development: Safe To Sleep: Fast Facts About SIDS. Accessed 02/01/2023.
Etiology of SIDS
The cause of SIDS is unknown, although it is most likely due to dysfunction of neural cardiorespiratory control mechanisms. The dysfunction may be intermittent or transient, and multiple mechanisms are probably involved. Factors that may be involved are the infant having a poor sleep arousal mechanism, an inability to detect elevated CO2 levels in the blood, or a cardiac channelopathy that affects heart rhythm.
Fewer than 5% of infants with SIDS have episodes of prolonged apnea before their death, so the overlap between the SIDS population and infants with recurrent prolonged apnea is very small.
Risk factors for SUID and SIDS
The definite association between a prone (on stomach) sleeping position and an increased risk of SUID has been documented strongly.
Other risk factors (see table Risk Factors for Sudden Unexpected Infant Death) include old or unsafe cribs, soft bedding (eg, lamb’s wool), waterbed mattresses, bed-sharing with a parent/caregiver, smoking in the home, and an overheated environment. Siblings of infants who die of SIDS are 5 times more likely to die of SIDS; it is not clear whether this is related to genetics or environment (including possible abuse by the affected infant's family).
Many risk factors for SIDS apply to SUID as well.
Risk Factors for Sudden Unexpected Infant Death
Bed-sharing with parent/caregiver |
Cold temperatures/winter months |
Episodes of apnea requiring resuscitation |
Growth failure |
Increased maternal parity |
Insufficient prenatal care |
Low birth weight |
Lower socioeconomic group |
Male sex |
Maternal age < 20 years |
Maternal drug use during pregnancy |
Maternal smoking during pregnancy |
Non-Hispanic American Indian/Alaska Natives, Non-Hispanic Blacks, and Non-Hispanic Native Hawaiian/Other Pacific Islanders race or ethnicity |
No pacifier |
Old or unsafe cribs |
Overheating (eg, blankets, hot room) |
Prone sleeping position* |
Recent illness |
Short interval between pregnancies |
Sibling of a SIDS victim |
Smoking in the home |
Soft bedding |
Waterbed mattress |
* Most important. |
SIDS = sudden infant death syndrome. |
Diagnosis of SIDS
Exclusion of other causes by autopsy
The diagnosis of SIDS, while largely one of exclusion, cannot be made without an adequate autopsy to rule out other causes of sudden, unexpected death (eg, intracranial hemorrhage, meningitis, myocarditis). An autopsy may be required in many states.
Also, the care team (including social workers) should sensitively assess the likelihood of infant suffocation or nonaccidental trauma (see Overview of Child Maltreatment); concern for this etiology should increase when the affected infant was outside the highest-risk age group (1 to 5 months) or another infant in the family had SUID or frequent brief, resolved, unexplained events (BRUEs).
Management of SIDS
Parents who have lost a child to SIDS are grief-stricken and unprepared for the tragedy. Because no definitive cause can be found for their child’s death, they usually have excessive guilt feelings, which may be aggravated by investigations conducted by police, social workers, or others. Family members require support not only during the days immediately after the infant’s death but for at least several months to help them with their grief and dispel guilt feelings. Such support includes, whenever possible, an immediate home visit to observe the circumstances in which SIDS occurred and to inform and counsel the parents concerning the cause of death.
Autopsy should be done quickly. As soon as the preliminary results are known (usually within 12 hours), they should be communicated to the parents. Some clinicians advise a series of home or office visits over the first month to continue the earlier discussions, answer questions, and give the family the final (microscopic) autopsy results. At the last meeting, it is appropriate to discuss the parents’ adjustment to their loss, especially their attitude toward having other children. Much of the counseling and support can be complemented by specially trained nurses or by lay people who have themselves experienced the tragedy of and adjustment to SIDS (visit the American SIDS Institute for more information and resources).
Prevention of SUID and SIDS
Clinicians, hospital staff, and child care providers must promote safe infant sleep practices from the beginning of pregnancy.
The American Academy of Pediatrics (see Sleep-Related Infant Deaths: Updated 2022 Recommendations for Reducing Infant Deaths in the Sleep Environment) recommends that infants be placed on their back on a firm, flat, non-inclined sleep surface for every sleep unless other medical conditions prevent this. Side sleeping or propping is too unstable. (See also the Safe to Sleep® campaign.)
The incidence of SIDS increases with overheating (eg, clothing, blankets, hot room) and in cold weather. Thus, every effort should be made to avoid an overly hot or an overly cold environment, to avoid overwrapping the infant or covering the head, and to remove loose bedding, such as blankets and non-fitted sheets, and soft bedding, such as sheepskin, pillows, stuffed toys/animals, mattress toppers, fur-like materials, quilts, and comforters, from the crib.
A pacifier is recommended at naptime and at bedtime to help open the airway and reduce the risk of SIDS.
Parents/caregivers should not have the infant sleep in their bed. It is recommended that infants sleep in the parents'/caregivers' room close to the parents'/caregivers' bed but on a separate surface designed for infants, ideally for at least the first 6 months.
To help prevent flat spots from developing on the infant's head, infants should spend some time on their tummy when they are awake and someone is watching them. Parents/caregivers should be encouraged to begin short periods of tummy time soon after hospital discharge, increasing incrementally to at least 15 to 30 minutes a day by age 7 weeks. To help make the infant's head round, parents/caregivers should change the direction that the infant lies in while in the crib each week and avoid leaving the infant for too long in car seats, carriers, and bouncers.
Breastfeeding is encouraged to help prevent infections and is associated with a reduced risk of SIDS.
Routine vaccinations are recommended for infants.
There is no evidence that home apnea monitors reduce the incidence of SIDS and therefore are not suggested for prevention. There is also no evidence to recommend swaddling for prevention of SIDS.
Key Points
Sudden unexpected infant death (SUID) is a term used to describe any unexpected and sudden death whether explained or unexplained in a child < 1 year of age, which often occurs during sleep or in the infant's sleep area.
Sudden infant death syndrome (SIDS) is a subset of SUID and is sudden and unexpected death in a child between 1 month and 1 year of age in which an examination of the death scene, thorough postmortem examination, and clinical history fail to show cause.
Specific causes, including child abuse, must be ruled out by clinical evaluation and autopsy.
Etiology is unclear, although a number of risk factors have been identified.
The most important modifiable risk factors involve the sleep setting, particularly prone sleeping, along with avoidance of bed-sharing and sleeping on very soft surfaces or with loose bedding.
Prior apneic episodes and brief, resolved, unexplained events (BRUEs) do not appear to be risk factors.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
American SIDS Institute: An organization providing education about causes of and ways to prevent SIDS and family support services
American Academy of Pediatrics: Sleep-Related Infant Deaths: Updated 2022 Recommendations for Reducing Infant Deaths in the Sleep Environment
Safe to Sleep®: Information for parents and caregivers about safe sleep practices for infants
