PEDIATRICS Vol. 108 No. 4 October 2001, pp. 923-927

Association Between Sudden Infant Death Syndrome and Prone Sleep Position, Bed Sharing, and Sleeping Outside an Infant Crib in Alaska

Bradford D. Gessner, MD, MPH, George C. Ives, MS, MPA, and Katherine A. Perham-Hester, MS, MPH

From the Alaska Division of Public Health, Anchorage, Alaska.

	ABSTRACT

Top Abstract Methods Results Discussion References

Objective.  To determine the contribution of prone sleeping, bed sharing, and sleeping outside an infant crib to sudden infant death syndrome (SIDS).

Methods.  We conducted a retrospective descriptive study of all SIDS cases in Alaska from January 1, 1992, through December 31, 1997. Reviewed data sources included maternal and infant medical records, autopsy reports, birth and death certificates, police and state trooper death scene investigations, and occasionally home interviews.

Results.  The death certificate identified SIDS as a cause of death for 130 infants (cause-specific infant mortality rate: 2.0 per 1000 live births). Among infants for whom this information was known, 113 (98%) of 115 were found in the prone position, sleeping outside an infant crib, or sleeping with another person. By contrast, 2 (1.7%) were found alone and supine in their crib (1 of whom was found with a blanket wrapped around his face). Of 40 infants who slept with a parent at the time of death, only 1 infant who slept supine with a non-drug-using parent on an adult nonwater mattress was identified.

Conclusion.  Almost all SIDS deaths in Alaska occurred in association with prone sleeping, bed sharing, or sleeping outside a crib. In the absence of other risk factors, SIDS deaths associated with parental bed sharing were rare.  Key words:  Alaska, bed sharing, drug use, prone sleeping, sudden infant death syndrome.

Sudden infant death syndrome (SIDS) has been defined as "the sudden death of an infant less than 1 year of age which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history."¹ A variety of factors, including parental drug use and infant physiologic abnormalities, have been implicated in SIDS.^2-6 More recently, investigators have identified associations between SIDS and prone sleeping position,^7,8 bed sharing with an adult,^9-13 and inappropriate bedding.^13-16 Despite these advances in the understanding of SIDS, the individual and collective contribution of multiple sleep-related risk factors for a statewide cohort of infant deaths remains undetermined. This information is important for designing, funding, and estimating the impact of public health interventions.

For the current study, we hypothesized that in Alaska (where SIDS rates are consistently among the highest in the United States^17,18), regardless of the presence of other risk factors, the majority of SIDS deaths occurred in association with prone sleeping position, sleeping with another person, or sleeping outside an infant crib. To test this hypothesis, we conducted a retrospective descriptive analysis of medical and other records collected as part of the Alaska Maternal-Infant Mortality Review (AMIMR) for infant deaths that occurred from January 1, 1992, through December 31, 1997.

	METHODS

Top Abstract Methods Results Discussion References

Data Sources

Our data source consisted of all records gathered as part of the AMIMR process. Infant deaths were identified through matched birth and death certificates from the Bureau of Vital Statistics. For each infant, a file was created that included birth and death certificates, infant and maternal medical records, autopsy reports, police and state trooper death scene investigations, and, if agreed to by the guardians of the deceased child, a home interview. Trained public health nurses conducted home interviews. Occasionally, the home interview provided the only source of information for sleep-related or other risk factors; usually, though, home interviews were either redundant or not available. Data from each of these sources were abstracted using a standard form and entered into a computer database.

Unlike infant mortality reviews conducted by most other states, AMIMR attempts to identify, collect information for, and review allrather than a subset ofresident infant deaths. For the current study, 97% of the known deaths were included. The remaining deaths were excluded because complete medical records were not available, usually because the deaths occurred in another state or because of pending litigation.

Case Identification

An infant was considered to have died of SIDS when the death certificate reported SIDS as the underlying or a contributing cause of death. We identified cases by reviewing death certificates for all infant deaths that occurred during the study period.

Background Characteristics of SIDS Cases

To provide a context for our investigation, we evaluated several factors associated with SIDS by other investigators, including maternal characteristics, infant physiologic abnormalities, and parental drug use. We determined the risk of SIDS associated with maternal demographic characteristicsincluding age, Alaska Native status, and educational attainmentby comparing birth certificate information for cases with all other live births in Alaska using a birth file provided by the Alaska Bureau of Vital Statistics.

Infant physiologic abnormalities included only substantial abnormalities, such as congenital anomalies, serious infections, and low birth weight. It was not known whether any of these abnormalities was necessary or sufficient to cause death. We present them here because previous studies documented an association between some abnormalities and SIDS deaths. Minor anomalies and mild infections, such as upper respiratory tract infection or mild gastroenteritis, were not included.

Parental drug use included prenatal or postnatal tobacco cigarette, alcohol, or illicit substance use. Because information on drug use was rarely available for caregivers other than parents, we limited this part of the analysis to infants who died while under parental care. Few of the records quantified the amount of drug use, so this information was not included. The medical records generally documented alcohol use only when it involved binge or chronic drinking, but this was not necessarily the case for every record.

Sleep-Related Factors

We determined the presence at the time of death of 3 sleep-related risk factors: infant sleep position, bed type, and the presence of other people in the infant's bed (bed sharing). Alaska is implementing a standard infant death scene investigation reporting form. At the time of the study, however, no standard form was used. Despite this limitation, for most SIDS cases information on the 3 risk factors of interest was available from the death scene investigation, home interview, or emergency department records. Infant sleep position was identified at the time the infant was found because the position when put down to sleep usually was not available and because the position at the time that the infant was found may reflect more accurately the position at the time of death. Because of the historically high SIDS rates among Alaska Natives, we present the prevalence of sleep-related risk factors by Alaska Native status.

Statistical Analysis

Rate ratios and their associated Taylor series 95% confidence intervals (CI) and exact 95% CIs for proportions were calculated with EpiInfo version 6.04 computer software (Centers for Disease Control and Prevention, Atlanta, GA).

	RESULTS

Top Abstract Methods Results Discussion References

Background Characteristics of SIDS Cases

Between January 1, 1992, and December 31, 1997, 501 Alaska resident infant deaths occurred (infant mortality rate: 7.9 per 1000 live births). Of the 488 deaths included in the study database, the death certificate reported the cause of death as SIDS for 130 (SIDS-specific infant mortality rate: 2.0 per 1000 live births). An autopsy was performed for 128 infants with 12 different pathologists completing the death certificates. Compared with other live births in Alaska, infants who died of SIDS were more likely to have mothers who were young, poorly educated, and of Alaska Native race (Table 1).

Of the 130 infants for whom the death certificate listed SIDS as a cause of death, 29 (22%) had 1 or more substantial physiologic abnormalities. Sixteen infants were born at <2500 g, 6 had pneumonia identified at autopsy, 3 had congenital heart disease identified at autopsy (1 infant each had an anomalous right coronary artery, ventricular septal defect, or pulmonary artery stenosis with right ventricular hypertrophy), and 1 infant each had an unspecified neurologic disorder, urinary tract infection, massive cerebral edema, severe malnutrition associated with renal anomalies, and severe malnutrition alone. For 4 infants, the death certificate reported 1 of the physiologic abnormalities described above, as well as SIDS, as a cause of death. Among Alaska Natives, 24% had a substantial physiologic abnormality compared with 19% of non-Natives.

Among infants who died of SIDS, parental drug use was common, including cigarette smoking (61% of infants), alcohol use (29%), and illicit substance use (15%); overall, 68% of infants had a parent with a documented history of any drug use. Most of the documented drug use occurred among mothers. Paternal drug use was documented for 8% of infants; paternal drug use in the absence of maternal drug use was documented for 1 infant. Among Alaska Natives, 94% of SIDS deaths occurred in association with a documented record of parental drug use, including 66% with a record of parental alcohol or illicit substance use. This compares with 50% and 19%, respectively, for non-Natives.

Sleep-Related Risk Factors

Bed Type Among 114 infants for whom bed type was known, 32% slept in an infant crib, 43% slept on an adult nonwater mattress, and the remainder slept on another surface (Table 2). Additional description of the specific type of adult nonwater mattresses used was not available. Most children who slept outside an infant crib slept with 1 or more other people, usually a parent. Among Alaska Natives, 82% slept outside an infant crib at the time of death compared with 59% of non-Natives.

Bed Sharing Among 110 infants for whom bed sharing information was known, 45% slept with at least 1 other person the night of death, usually 1 or both parents (Table 2). Two infants were found underneath a parent, and a third had a fabric impression on his face. Among Alaska Native infants, 60% slept with another person the night of death compared with 35% of non-Natives.

Sleep Position Among infants for whom sleep position was known, 2 of 33 (6.1%) deaths that took place in an infant crib occurred in association with the supine or side sleep position (Fig 1). By contrast, 23 of 57 (40%) deaths that occurred outside an infant crib involved the supine or side sleep position. Among Alaska Natives, 68% were found in the prone position compared with 76% of non-Natives.

View larger version (13K): [in this window] [in a new window]   Fig. 1.   Bedding and sleep position at the time of death for 130 infants with SIDS, Alaska, 1992-1997.

Summary Of the 115 infants for whom risk factor information was known, 2 (1.7%; exact 95% CI: 0.21%-6.1%) occurred to infants who slept alone, in the side or supine position, and in a crib. Of these 2 infants, 1 was found with a blanket wrapped around his head. The remaining 113 deaths occurred to infants who slept outside an infant crib, in the prone position, or with another person. For 15 deaths, adequate information on sleep-related risk factors did not exist. For these deaths, no sleep-related risk factor information could be found for 9 infants, whereas 6 had information available for 1 or 2 but not all risk factors. When analysis included only infants for whom all sleep-related risk factor information was known, 2 of 84 (2.4%; exact 95% CI: 0.29-8.3) were found alone, in the side or supine position, and in a crib at death.

	DISCUSSION

Top Abstract Methods Results Discussion References

We evaluated all cases of SIDS from an entire state over an extended period using a comprehensive collection of data sources. As with other studies, SIDS deaths frequently occurred in association with infant physiologic abnormalities and parental drug use. Despite this, we found that all but 2 cases of SIDS for whom this information was known occurred in the context of prone sleep position,^7,8 bed sharing,^9-12 or sleeping outside an infant crib.^14,16 Both non-Natives and Alaska Natives had high prevalences of all 3 risk factors, although a substantially higher proportion of Native infants died while bed sharing.

The current study was descriptive and hence uncontrolled. Nevertheless, some background information is available from the Alaska Pregnancy Risk Assessment Monitoring System, a population-based mail survey of Alaska resident women who recently delivered a live infant.^19,20 The Pregnancy Risk Assessment Monitoring System found that in Alaska during 1996 to 1998, 66% of infants sometimes or never slept with their mother (possible survey responses include always, usually, sometimes, or never), 83% usually were placed in the supine or side position, and a combined 55% had both characteristics (Alaska Division of Public Health, unpublished data). Consequently, if drug use or physiologic abnormalities in the absence of sleep-related factors frequently caused SIDS, then we should have identified more than 2 deaths among infants sleeping supine in their crib (1 of whom had an obvious cause of death).

SIDS deaths among infants who slept in an infant crib occurred almost exclusively in association with prone sleep position. If the evaluated sleep-related risk factors formed part of the causal chain of death, this is a necessary finding because infants who slept alone in their crib by definition were not exposed to the other 2 risk factors. By contrast, for infants who were found outside an infant crib, prone position should be of less importance because such potential mechanisms as overlying or suffocation as a result of inappropriate bedding materials do not require the presence of a prone infant. As predicted, the current study found that 40% of deaths that occurred outside an infant crib involved the side or supine position. This result also supports studies that found that programs that promote supine sleeping have been associated with a decrease but not an elimination of SIDS deaths.^21-23

Recently, researchers using Consumer Product Safety Commission datawith limited information on some pertinent risk factors, such as parental drug usehave recommended against bed sharing of any kind.^13,24 Our data do not support this recommendation. Almost all SIDS deaths associated with parental bed sharing occurred in conjunction with a history of parental drug use^9,12 and occasionally in association with the prone sleep position or sleeping on surfaces such as couches or waterbeds. We found just 1 death of an infant whose only risk factor was sleeping with a non-drug-using parent on an adult nonwater mattress. In our population, this was true regardless of the specific characteristics of the adult mattress used. Because of these findings, the State of Alaska does not counsel caregivers to avoid bed sharing with their infants. Instead, a simple public health message that is consistent with the existing data has been developed: infants should sleep in the supine position and in their crib or with an unimpaired caregiver on an adult nonwater mattress.

At least 3 limitations affect the interpretation and generalizability of our results. We collected sleep position at the time the infant was found rather than at the time of sleep. Neither time may reflect accurately the position of the infant at the moment of death because infants may change position during sleep, including as a result of bed sharing. We relied on a retrospective evaluation of a variety of records to identify the outcomes of interest rather than using a prospective standardized interview form. The unique characteristics of Alaskaincluding cold winters, large rural populations, and a large aboriginal population with a high risk of SIDSmay support different risk factors than other areas of the world.

Because of the above limitations, the current study does not provide definitive support for a causal association between sleep-related risk factors and SIDS. Future controlled studies examining the 3 sleep-related risk factors of interest may provide stronger evidence. Until that time, however, the available data suggest that in Alaska, sleep-related factors may form part of the chain of events that lead to SIDS. This finding has important implications because sleep-related factors are more amenable to public health interventions than many of the other factorssuch as low birth weight, parental drug use, race, and socioeconomic statuspreviously associated with SIDS.

Building on the success of the Back to Sleep campaign, the American Academy of Pediatrics Task Force on Infant Positioning and SIDS recently issued recommendations that infants be placed to sleep in infant cribs and not on sofas, waterbeds, or soft mattresses and that bed sharing with a drug-impaired caregiver is hazardous to infants.²³ Our data suggest that promotion and implementation of these recommendations will lead to a decrease in SIDS cases. Our data do not support avoiding bed sharing of any kind or the need for a specific type of adult nonwater mattress for parents who choose to bed share. The public health message adopted by Alaska is that infants should sleep in the supine position and either in an infant crib or with a nonsmoking, unimpaired caregiver on an adult nonwater mattress.

	FOOTNOTES

Received for publication Sep 19, 2000; accepted Jan 26, 2001.

Reprint requests to (B.D.G.) Alaska Division of Public Health, Section of Maternal, Child, and Family Health, 3601 C St, Suite 934, Box 240249, Anchorage, AK 99524-0249. E-mail: brad_gessner{at}health.state.ak.us

	ABBREVIATIONS

SIDS, sudden infant death syndrome; AMIMR, Alaska Maternal-Infant Mortality Review; CI, confidence interval.

	REFERENCES

Top Abstract Methods Results Discussion References

1. Willinger M, James LS, Catz C Defining the sudden infant death syndrome (SIDS): deliberations of an expert panel convened by the National Institute of Child Health and Human Development. Pediatr Pathol 1991; 11:677-684 [Medline]
2. Blackwell CC, Weir DM The role of infection in sudden infant death syndrome. FEMS Immunol Med Microbiol 1999; 25:1-6 [CrossRef][Medline]
3. Dwyer T, Ponsonby AL, Couper D Tobacco smoke exposure at one month of age and subsequent risk of SIDS: a prospective study. Am J Epidemiol 1999; 149:593-602 [Abstract/Free Full Text]
4. Schwartz PJ, Stramba-Badiale M, Segantini A, Prolongation of the QT interval and the sudden infant death syndrome. N Engl J Med 1998; 338:1709-1714 [Abstract/Free Full Text]
5. Ozawa Y, Obonai T, Itoh M, Aoki Y, Funayama M, Takashima S Catecholaminergic neurons in the diencephalon and basal ganglia of SIDS. Pediatr Neurol 1999; 21:471-475 [CrossRef][Medline]
6. Mallard C, Tolcos M, Leditschke J, Campbell P, Rees S Reduction in choline acetyltransferase immunoreactivity but not muscarinic-m2 receptor immunoreactivity in the brainstem of SIDS infants. J Neuropathol Exp Neurol 1999; 58:255-264 [Medline]
7. Skadberg BT, Morild I, Markestad T Abandoning prone sleeping: effect on the risk of sudden infant death syndrome. J Pediatr 1998; 132:340-343 [CrossRef][Medline]
8. Dwyer T, Ponsonby AL, Newman NM, Gibbons LE Prospective cohort study of prone sleeping position and sudden infant death syndrome. Lancet 1991; 337:1244-1247 [CrossRef][Medline]
9. Scragg RK, Mitchell EA Side sleeping position and bed sharing in the sudden infant death syndrome. Ann Med 1998; 30:345-349 [Medline]
10. Fleming PJ, Blair PS, Bacon C, Environment of infants during sleep and risk of the sudden infant death syndrome: results of 1993-5 case-control study for confidential inquiry into stillbirths and deaths in infancy. Confidential Enquiry into Stillbirths and Deaths Regional Coordinators and Researchers. BMJ 1996; 313:191-195 [Abstract/Free Full Text]
11. Klonoff-Cohen H, Edelstein SL Bed sharing and the sudden infant death syndrome. BMJ 1995; 311:1269-1272 [Abstract/Free Full Text]
12. Blair PS, Fleming PJ, Smith IJ, , and the CESDI SUDI research group. Babies sleeping with parents: case-control study of factors influencing the risk of the sudden infant death syndrome. BMJ 1999; 319:1457-1462 [Abstract/Free Full Text]
13. Nakamura S, Wind M, Danello MA Review of hazards associated with children placed in adult beds. Arch Pediatr Adolesc Med 1999; 153:1019-1023 [Abstract/Free Full Text]
14. Mitchell EA, Thompson JM, Ford RP, Taylor BJ Sheepskin bedding and the sudden infant death syndrome. New Zealand Cot Death Study Group. J Pediatr 1998; 133:701-704 [CrossRef][Medline]
15. Kemp JS, Livne M, White DK, Arfken CL Softness and potential to cause rebreathing: differences in bedding used by infants at high and low risk for sudden infant death syndrome. J Pediatr 1998; 132:234-239 [CrossRef][Medline]
16. Ramanathan R, Chandra S, Gilbert-Barness E, Franciosi R Sudden infant death syndrome and water beds. N Engl J Med 1988; 318:1700 [Medline]
17. National Center for Health Statistics. Health, United States, 1999, With Health and Aging Chartbook. Hyattsville, MD; 1999
18. Kraus JF, Bulterys M. The epidemiology of sudden infant death syndrome. In: Kiely M, ed. Reproductive and Perinatal Epidemiology. Boca Raton, FL: CRC Press; 1991:219-249
19. Adams MM, Shulman HB, Bruce C, Hogue C, Brogan D The PRAMS Working Group. The Pregnancy Risk Assessment Monitoring System: design, questionnaire, data collection and response rates. Paediatr Perinat Epidemiol 1991; 5:333-346 [Medline]
20. Gessner BD, Perham-Hester KA The experience of violence among teenage mothers in Alaska. J Adolesc Health 1998; 22:383-388 [CrossRef][Medline]
21. Centers for Disease Control and Prevention Progress in reducing risky infant sleeping positions13 states, 1996-1997. MMWR Morb Mortal Wkly Rep 1999; 48:878-882 [Medline]
22. CDC Sudden infant death syndromeUnited States, 1983-94. MMWR Morb Mortal Wkly Rep 1996; 45:859-863 [Medline]
23. American Academy of Pediatrics, Task Force on Infant Sleep Position and Sudden Infant Death Syndrome Changing concepts of sudden infant death syndrome: implications for infant sleeping environment and sleep position. Pediatrics 2000; 105:650-656 [Abstract/Free Full Text]
24. Drago DA, Dannenberg AL. Infant mechanical suffocation deaths in the United States, 1980-1997. Pediatrics. 1999;103(5). Available at: http://www.pediatrics.org/cgi/content/full/103/5/e59