In the United States, approximately 4,000 infants die yearly from sleep-related deaths, referred to as sudden unexpected infant deaths (SUIDs).1 These deaths occur suddenly and may be explained or unexplained among infants younger than age 1 year, and they are commonly reported as sudden infant death syndrome (SIDS), death from unknown cause, and death from accidental suffocation and strangulation in bed. SIDS comprises approximately one-half of all SUIDs and is characterized by the sudden, unexplained death of a seemingly healthy infant with the cause of death remaining unknown despite a thorough investigation including review of the clinical history, examination of the death scene, and complete autopsy. Most SIDS deaths occur during the first 6 months of life, predominantly between ages 2 and 4 months. Since the launch of the Back to Sleep campaign in 1994 by the American Academy of Pediatrics (AAP), the overall SIDS rate in the US has declined by more than 50%, from 130 deaths per 100,000 live births (∼5,000) in 1990 to 40 deaths per 100,000 live births (∼1,600 deaths) in 2015.1 Nonetheless, SIDS remains the second leading cause of postneonatal death and the fourth leading cause of infant mortality in the US.2 In recent years, the rate of SIDS has remained stationary despite major public health efforts aimed at improving infant's sleep environment and focusing on high-risk groups. SIDS affects families of all social, economic, and ethnic backgrounds. However, it is more likely to occur in babies born to mothers with limited or inadequate prenatal care, mothers who smoke during pregnancy, male infants (male-to-female ratio of 3:2), prone and side-lying position during sleep, preterm or low birth weight infants, and in Native American/Alaska Native and non-Hispanic black infants.3
SIDS is not completely preventable, but it is thought that risk can be decreased by following the fundamental “ABC” of safe sleep. This means having the infant sleep “Alone” and not with other people, not sleeping with pillows, loose blankets, or stuffed animals; having the infant sleep on his or her “Back” and not prone or side-lying position; and having the infant sleep in his or her own “Crib,” and not on an adult bed, sofa, cushion, or other soft surface.
Pathogenesis and Risk Factors
Current evidence suggests a triple-risk model for the pathogenesis of SIDS, in which an infant with underlying vulnerability is subjected to an extrinsic risk factor during a critical stage of his or her development (Figure 1). In this model, intrinsic and extrinsic risk factors must coincide during a period (typically age 2 to 4 months) when significant developmental, respiratory, autonomic, and cardiac changes are taking place.4,5 The combination of these factors leads toward a terminal respiratory pathway, and death occurs when protective mechanisms fail in the face of a life-threatening event.6
Triple-risk model for sudden infant death syndrome. IUGR, intrauterine growth restricted; SIDS, sudden infant death syndrome. Adapted from Filiano and Kinney.5
Intrinsic risk factors for SIDS are the least understood component of the triple risk model, but research suggests that brain and brainstem abnormalities, particularly those associated with neuroregulation and cardiorespiratory function, play an important role in SIDS.7 The serotonin system has been the focus of research due to its close association with numerous homeostatic functions. Serotonin receptor abnormalities such as deviations in 5-hydroxytryptamine binding have been identified in the medulla of as many as 70% of SIDS victims, and gene mutations associated with the autonomic nervous system are found in up to 15% of cases.7,8 Genetic variations in sodium and potassium channel function have also been proposed, including polymorphisms in the sodium channel gene, SCN5A, which may alter autonomic system development and be associated with prolonged QT interval.9
Infants born premature or those with intrauterine growth restriction are more likely to succumb to SIDS, suggesting that a suboptimal intrauterine environment may play a role in pathogenesis.10 Prenatal exposure to tobacco smoke, in particular, has been shown to put infants at increased risk because it alters recovery from hypoxia, results in impaired arousal patterns, and disrupts both autonomic function and cardiovascular reflexes.11,12
Extrinsic risk factors for SIDS provide an environmental trigger to the already vulnerable infant. Prone sleep position remains the most significant risk factor for SIDS by increasing the likelihood of re-breathing expired gases, suffocation, overheating, and decreased arousal.13 Side-lying position carries similar risk, particularly when the infant is placed on his or her side to sleep but rolls into prone position.14 Other environmental risk factors include soft or loose bedding and bumper pads, which increase the likelihood of SIDS up to 5 times.15,16 An association between bed-sharing and SIDS has also been demonstrated, especially in infants younger than age 3 months or when additional risk factors are present, such as cigarette smoke, maternal alcohol use, or bottle-feeding.17 Risk is further amplified when co-sleeping occurs on a couch or sofa.18
Multiple intrinsic and extrinsic factors ultimately lead to asphyxia in a vulnerable infant with insufficient arousal mechanisms and cardiorespiratory function.6 In this setting, a life-threatening event and/or environmental condition occurs during sleep. Due to intrinsic vulnerability, the infant is not able to arouse to avoid re-breathing or recover from apnea. As a result, continued asphyxia occurs leading to bradycardia, ineffective gasping mechanisms, and eventually death.19,20 Each of these factors, when taken on its own, is much less significant than the combination of multiple, precisely timed events.
AAP Recommendations on Safe Infant Sleeping Environment
The AAP Task Force on SIDS recently published updated recommendations aimed at reducing the risk of sleep-related infant deaths, including SIDS (Table 1).7 These recommendations are largely based on case-control studies targeting infants younger than age 1 year, and the strength of the recommendations is based on the strength of recommendation taxonomy (SORT).21
Summary of AAP Recommendations for Safe Sleep with SORT
The sleeping position is the strongest modifiable risk factor for SIDS.7,22,23 Infants should be placed to sleep in supine position until age 1 year or until the infant can roll from supine to prone and back again. Prone and side-lying sleeping positions are dangerous and should be avoided because they are associated with increased risk of hypercapnia, hypoxia, altered autonomic control of the infant's cardiovascular system, and increased arousal thresholds.13,24,25 Contrary to common belief, supine sleeping position does not increase the risk of choking or aspiration, even in those infants diagnosed with gastroesophageal reflux, due to airway protective mechanisms that will prevent aspiration.26 In addition, the upper airway sits anatomically above the esophagus in a supine position, making it harder for any regurgitated milk to be aspirated.
Use of a firm flat surface covered by a fitted sheet to sleep is strongly recommended, and soft bedding accessories should be avoided due to risk of suffocation, strangulation, and/or entrapment. Sitting devices (eg, strollers and car seats) and positioning devices (eg, wedges and bumpers) should not be used while sleeping due to increased risk of injury and airway obstruction leading to unintentional deaths. The use of home cardiorespiratory monitors has not been proven to reduce the incidence of SIDS and might potentially distract from other proven preventive measures that reduce SIDS.
Breast-feeding or feeding with expressed breast-milk should be encouraged unless contraindicated. Studies have shown that breast-feeding is protective against SIDS;27,28 however, the benefit is more pronounced when infants are exclusively breast-fed. A large meta-analysis study of breastfeeding and SIDS risk found that infants who were exclusively breast-fed had an odds ratio (OR) for SIDS of 0.27 (95% confidence interval [CI] 0.24-0.31) compared with infants who were not breast-fed.27 The use of a pacifier for naps and bedtime is also associated with lower risk of SIDS, although the exact mechanism of protection is unknown.28 However, the AAP suggests postponing pacifier use until breast-feeding is well established.7 In addition, pacifiers should not be attached to straps or cords as these might introduce risk for strangulation.
Several studies report an association between SIDS and bed-sharing.17,29 The AAP recommends that infants sleep in their parent's room but bed-sharing is prohibited until the child's first birthday, or at least during the first 6 months of life when the risk of SIDS and other sleep-related deaths is relatively high.7 The increased risk could be related to overheating of the infant, sharing of soft mattresses, and being rolled over by an adult. In addition, the use of nicotine, illicit drugs, and alcohol by the primary caregiver while sharing the bed with the infant may exacerbate the situation and play a significant role in the incidence of SIDS. A meta-analysis that included 11 studies showed that the OR for SIDS in all bed-sharing versus non–bed-sharing infants was 2.89 (95% CI 1.99–4.18). The highest risk was in infants of smoking mothers (OR 6.27; 95% CI 3.94–9.99), and infants younger than age 12 weeks (OR 10.37; 95% CI 4.44–24.21).30
Swaddling as a strategy to promote sleep and calm an infant has not been shown to reduce the incidence of SIDS. Recent studies have shown an increased risk of death if a swaddled infant is placed in or rolls to the prone position for sleep.31 Regular prenatal care and routine immunizations for infants are strongly recommended by the AAP and US Centers for Disease Control and Prevention (CDC).7 A supervised, awake and alert prone position or “tummy time” is recommended to help minimize plagiocephaly and facilitate motor development.
Education about and implementation of safe sleep practices by health care professionals and child care providers should be based on the model of SIDS risk-reduction recommendations. In addition, the AAP recommends that such education should start early and include training of teenage and adult babysitters. Lastly, the AAP encourages the continued research on SIDS and other sleep-related infant deaths, with the goal of eliminating these deaths completely.7
SIDS/SUID Case Registry and Reporting
SIDS and accidental suffocation and strangulation in bed are the most commonly reported types of SUID.1 The cause of a SUID is based on the outcome of a medico-legal investigation but may remain unexplained despite thorough investigation. Inconsistent practices in the death scene analysis, surrounding events, and data reporting seriously impair the ability of researchers to characterize SIDS/SUID trends and characteristics. Recognizing the need for a consistent approach to data collection at an infant death scene investigation and to improve reporting methodology and consistency of SUID classification terminology, the CDC in 2009 developed the SIDS/SUID Case Registry, a multistate SIDS/SUID surveillance and reporting system.32 To that end, the CDC developed standardized guidelines for death scene investigation, created data collection forms, and a web-based reporting system. The development and dissemination of the SUID investigation reporting form was extremely important as a tool to standardized data collection, to improve the classification of sleep-related infant deaths, and help investigative agencies more clearly understand the circumstances and factors contributing to unexplained infant deaths.33 To implement these changes, the CDC developed educational materials and conducted training to educate medico-legal professionals in the use of these investigative tools and forms.1
The SUID Case Registry data is integrated with the preexisting National Center for Fatality Review and Prevention System and brings together information about the circumstances associated with SUID cases as well as information about investigations into these deaths.34
The SIDS/SUID Case Registry is maintained by the CDC's Division of Reproductive Health.32 The CDC and the National Institutes of Health fund participants in the SUID monitoring program. As of 2017, SUID fund grantees in 16 states and two jurisdictions covered approximately 30% of all SUID events in the United States.32 Participants include Arizona, Colorado, Louisiana, Michigan, Minnesota, New Jersey, New Mexico, New Hampshire, Wisconsin, Alaska, Kentucky, Pennsylvania, Delaware, Georgia, Tennessee, Nevada, the city and county of San Francisco, and the Tidewater Region of Virginia.1 Participation is voluntary and those states and jurisdictions that participate in the SIDS/SUID monitoring program receive additional technical assistance and resources from the CDC.
The grantee participants (state health departments or their representatives) follow a structured process in all SIDS/SUID wherein the cases are first identified by the medical examiner, coroner, or state vital statistics office. Investigators then review information from death scene investigations, autopsies, medical records, and other medico-legal reports and try to identify actionable strategies that may reduce SIDS/SUID and improve case investigations. Findings are then entered into a web-based reporting system. The data are then analyzed to identify SIDS/SUID trends and characteristics and used to inform strategies and recommendations to reduce future deaths.35 In addition, the CDC makes available to physicians and medical examiners of all states, not just grantees, the ability to submit bio-specimens for evaluation to the CDC's Infectious Diseases Branch in instances where clinical or laboratory information suggests infection as a cause of death.36
The ultimate outcome of the SIDS/SUID Case Registry activities is that the CDC and state grantees use the case registry surveillance data to monitor trends and characteristics, modify public health practice for state maternal and child health programs, encourage more consistent medico-legal investigation and reporting practices, and improve systems of care for families and develop targeted prevention strategies such as safe sleep education and promotion.1
There is no federal law that requires states to participate in the CDC's SIDS/SUID initiative. For those states that do not participate in the SIDS/SUID Registry or CDC grantee process (approximately 70%), most have passed laws regarding SIDS/SUID deaths.34 The laws in these states may vary significantly, both in scope and subject, but most states have benefited from the CDC initiative by modeling their SIDS/SUID laws largely on CDC recommendations. Most states have laws that set a protocol for autopsies of SIDS and/or SUID cases and require participation of a SIDS expert in child fatality review. Some states mandate SIDS/SUID advisory councils, education programs, or counseling programs, and require data collection for use in research. Although the CDC requires special training when investigating a SIDS/SUID for child care personnel, firefighters, emergency medical technicians, or law enforcement officials, only a minority of the states do so as of 2015.34,37 Clearly, the CDC has been a major driving force to better understand, educate, and devise strategies to reduce SIDS, but more could be accomplished with greater participation of the states or the enactment of national legislation.
SIDS is a complex, multifactorial disorder for which continued research is needed to more completely understand the relevant interplay of innate vulnerability, a critical developmental period, and the presence of environmental risk factors. Although SIDS may never be completely eliminated, we can hope that through better education and implementation of safe sleep practices from hospital to home that we can carve away this diagnosis of exclusion to its minimum. Parents and caregivers must understand that despite the unknown nature and cause of SIDS, altering certain behaviors, practices, and interventions may influence the ultimate outcome of an event. It is important for physicians, nurses, and other health care professionals to provide a consistent message and address parents and caregiver concerns and misconceptions about safe sleep recommendations. A SIDS/SUID case registry may increase knowledge on factors surrounding SIDS/SUID events and could help develop additional targeted preventive strategies to prevent this tragic event.
- Centers for Disease Control and Prevention. About sudden unexpected infant death and sudden infant death syndrome. https://www.cdc.gov/sids/aboutsuidandsids.htm. Accessed February 21, 2018.
- Shapiro-Mendoza CK, Camperlengo L, Ludvigsen R, et al. Classification system for the Sudden Unexpected Infant Death Case Registry and its application. Pediatrics. 2014;134(1):e210–e219. doi:. doi:10.1542/peds.2014-0180 [CrossRef]
- Heron M. Deaths: leading causes for 2014. Natl Vital Stat Rep. 2016;65(5):1–96.
- Goldstein RD, Kinney HC, Willinger M. Sudden unexpected death in fetal life through early childhood. Pediatrics. 2016;137(6):e20154661. doi:. doi:10.1542/peds.2015-4661 [CrossRef]
- Filiano JJ, Kinney HC. A perspective on neuropathologic findings in victims of the sudden infant death syndrome: the triple-risk model. Biol Neonate. 1994;65(3–4):194–197. doi:. doi:10.1159/000244052 [CrossRef]
- Kinney HC, Thach BT. The sudden infant death syndrome. N Engl J Med. 2009;361(8):795–805. doi:. doi:10.1056/NEJMra0803836 [CrossRef]
- Moon RYTask Force on Sudden Infant Death Syndrome. SIDS and other sleep-related infant deaths: evidence base for 2016 updated recommendations for a safe infant sleeping environment. Pediatrics. 2016;138(5):e20162940. doi:. doi:10.1542/peds.2016-2940 [CrossRef]
- Weese-Mayer DE, Berry-Kravis EM, Zhou L, et al. Sudden infant death syndrome: case-control frequency differences at genes pertinent to early autonomic nervous system embryologic development. Pediatr Res. 2004;56(3):391–395. doi:. doi:10.1203/01.PDR.0000136285.91048.4A [CrossRef]
- Plant LD, Bowers PN, Liu Q, et al. A common cardiac sodium channel variant associated with sudden infant death in African Americans, SCN5A S1103Y. J Clin Invest. 2006;116(2):430–435. doi:. doi:10.1172/JCI25618 [CrossRef]
- Bigger HR, Silvestri JM, Shott S, Weese-Mayer DE. Influence of increased survival in very low birth weight, low birth weight, and normal birth weight infants on the incidence of sudden infant death syndrome in the United States: 1985–1991. J Pediatr. 1998;133(1):73–78. doi:10.1016/S0022-3476(98)70181-7 [CrossRef]
- Fifer WP, Fingers ST, Youngman M, Gomez-Gribben E, Myers MM. Effects of alcohol and smoking during pregnancy on infant autonomic control. Dev Psychobiol. 2009;51(3):234–242. doi:. doi:10.1002/dev.20366 [CrossRef]
- Richardson HL, Walker AM, Horne RS. Maternal smoking impairs arousal patterns in sleeping infants. Sleep. 2009;32(4):515–521. doi:10.1093/sleep/32.4.515 [CrossRef]
- Groswasser J, Simon T, Scaillet S, Franco P, Kahn A. Reduced arousals following obstructive apneas in infants sleeping prone. Pediatr Res. 2001;49(3):402–406. doi:. doi:10.1203/00006450-200103000-00015 [CrossRef]
- Li DK, Petitti DB, Willinger M, et al. Infant sleeping position and the risk of sudden infant death syndrome in California, 1997–2000. Am J Epidemiol. 2003;157(5):446–455. doi:10.1093/aje/kwf226 [CrossRef]
- Wilson CA, Taylor BJ, Laing RM, Williams SM, Mitchell EA. Clothing and bedding and its relevance to sudden infant death syndrome: further results from the New Zealand Cot Death Study. J Paediatr Child Health. 1994;30(6):506–512. doi:10.1111/j.1440-1754.1994.tb00722.x [CrossRef]
- Scheers NJ, Dayton C, Kemp JS. Sudden infant death with external airways covered: case-comparison study of 206 deaths in the united states. Arch Pediatr Adolesc Med. 1998;152(6):540–547. doi:10.1001/archpedi.152.6.540 [CrossRef]
- Ruys JH, de Jonge GA, Brand R, Engelberts AC, Semmekrot BA. Bed-sharing in the first four months of life: a risk factor for sudden infant death. Acta Paediatr. 2007;96(10):1399–1403. doi:. doi:10.1111/j.1651-2227.2007.00413.x [CrossRef]
- Rechtman LR, Colvin JD, Blair PS, Moon RY. Sofas and infant mortality. Pediatrics. 2014;134(5):e1293–e1300. doi:. doi:10.1542/peds.2014-1543 [CrossRef]
- Sridhar R, Thach BT, Kelly DH, Henslee JA. Characterization of successful and failed autoresuscitation in human infants, including those dying of SIDS. Pediatr Pulmonol. 2003;36(2):113–122. doi:. doi:10.1002/ppul.10287 [CrossRef]
- Poets CF. Apparent life-threatening events and sudden infant death on a monitor. Paediatr Respir Rev. 2004;5(suppl A):S383–386. doi:10.1016/S1526-0542(04)90068-1 [CrossRef]
- Ebell MH, Siwek J, Weiss BD, et al. Strength of recommendation taxonomy (SORT): a patient-centered approach to grading evidence in the medical literature. J Am Board Fam Pract. 2004;17(1):59–67. doi:10.3122/jabfm.17.1.59 [CrossRef]
- Vennemann MM, Findeisen M, Butterfass-Bahloul T, et al. Modifiable risk factors for SIDS in Germany: results of GeSID. Acta Paediatr. 2005;94(6):655–660. doi:. doi:10.1080/08035250410024231 [CrossRef]
- Carpenter RG, Irgens LM, Blair PS, et al. Sudden unexplained infant death in 20 regions in Europe: case control study. Lancet. 2004;363(9404):185–191. doi:10.1016/S0140-6736(03)15323-8 [CrossRef]
- Colvin JD, Collie-Akers V, Schunn C, Moon RY. Sleep environment risks for younger and older infants. Pediatrics. 2014;134(2):e406–e412. doi:. doi:10.1542/peds.2014-0401 [CrossRef]
- Yiallourou SR, Walker AM, Horne RS. Prone sleeping impairs circulatory control during sleep in healthy term infants: implications for SIDS. Sleep. 2008;31(8):1139–1146.
- Tablizo MA, Jacinto P, Parsley D, Chen ML, Ramanathan R, Keens TG. Supine sleeping position does not cause clinical aspiration in neonates in hospital newborn nurseries. Arch Pediatr Adolesc Med. 2007;161(5):507–510. doi:. doi:10.1001/archpedi.161.5.507 [CrossRef]
- Hauck FR, Thompson JM, Tanabe KO, Moon RY, Vennemann MM. Breastfeeding and reduced risk of sudden infant death syndrome: a meta-analysis. Pediatrics. 2011;128(1):103–110. doi:. doi:10.1542/peds.2010-3000 [CrossRef]
- Hauck FR, Omojokun OO, Siadaty MS. Do pacifiers reduce the risk of sudden infant death syndrome? A meta-analysis. Pediatrics. 2005;116(5):e716–e723. doi:. doi:10.1542/peds.2004-2631 [CrossRef]
- Horsley T, Clifford T, Barrowman N, et al. Benefits and harms associated with the practice of bed sharing: a systematic review. Arch Pediatr Adolesc Med. 2007;161(3):237–245. doi:. doi:10.1001/archpedi.161.3.237 [CrossRef]
- Vennemann MM, Hense HW, Bajanowski T, et al. Bed sharing and the risk of sudden infant death syndrome: can we resolve the debate?J Pediatr. 2012;160(1):44–48.e2. doi:. doi:10.1016/j.jpeds.2011.06.052 [CrossRef]
- Pease AS, Fleming PJ, Hauck FR, et al. Swaddling and the risk of sudden infant death syndrome: a meta-analysis. Pediatrics. 2016;137(6): e20153275. doi:. doi:10.1542/peds.2015-3275 [CrossRef]
- Centers for Disease Control and Prevention. SUID and SDY case registries. https://www.cdc.gov/sids/caseregistry.htm. Accessed February 21, 2018.
- Centers for Disease Control and Prevention. How to use SUIDI reporting forms. https://www.cdc.gov/sids/pdf/HowtoUseSUIDIForms-508.pdf. Accessed February 21, 2018.
- The National Center for Fatality Review and Prevention. National CDR case reporting system. https://www.ncfrp.org/resources/national-cdr-case-reporting-system. Accessed February 21, 2018.
- Camperlengo L, Shapiro-Mendoza CK, Gibbs F. Improving sudden unexplained infant death investigation practices: an evaluation of the Centers for Disease Control and Prevention's SUID Investigation Training Academies. Am J Forensic Med Pathol. 2014;35(4):278–282. doi:. doi:10.1097/PAF.0000000000000123 [CrossRef]
- Center for Disease Control and Prevention. Specimen submission guidelines for pathologic evaluation of sudden unexplained infant death with pathologic or clinical suspicion of infection. https://www.cdc.gov/ncezid/dhcpp/idpb/specimen-submission/suid.html. Accessed February 21, 2018.
- National Conference of State Legislatures. Sudden unexpected infant death legislation. Updated March 2015. http://www.ncsl.org/research/health/sudden-infant-death-syndrome-laws.aspx. Accessed March 1, 2018.
Summary of AAP Recommendations for Safe Sleep with SORT
||SORT Letter Grade20
|Back to sleep for every sleep
|Use of firm sleep surface
|Room-sharing without bed-sharing
|Avoid using soft objects and loose bedding
|Offer pacifier at naptime and bedtime
|Avoid smoke exposure, alcohol, and illicit drug use during pregnancy and after birth
|Regular prenatal care
|Do not use home cardiorespiratory monitors
|Avoid use of commercial devices inconsistent with safe sleep recommendations
|Supervised and awake tummy time