Describe characteristics of sudden unexpected infant deaths (SUID) occurring on shared or nonshared sleep surfaces.
We examined SUID among residents of 23 US jurisdictions who died during 2011 to 2020. We calculated frequencies and percentages of demographic, sleep environment, and other characteristics by sleep surface sharing status and reported differences of at least 5% between surface sharing and nonsharing infants.
Of 7595 SUID cases, 59.5% were sleep surface sharing when they died. Compared with nonsharing infants, sharing infants were more often aged 0 to 3 months, non-Hispanic Black, publicly insured, found supine, found in an adult bed or chair/couch, had a higher number of unsafe sleep factors present, were exposed to maternal cigarette smoking prenatally, were supervised by a parent at the time of death, or had a supervisor who was impaired by drugs or alcohol at the time of death. At least 76% of all SUID had multiple unsafe sleep factors present. Among surface-sharing SUID, most were sharing with adults only (68.2%), in an adult bed (75.9%), and with 1 other person (51.6%). Surface sharing was more common among multiples than singletons.
Among SUID, surface sharing and nonsharing infants varied by age at death, race and ethnicity, insurance type, presence of unsafe sleep factors, prenatal smoke exposure, and supervisor impairment. Most SUID, regardless of sleep location, had multiple unsafe sleep factors present, demonstrating the need for comprehensive safe sleep counseling for every family at every encounter.
Sleep surface sharing, soft bedding, and prone sleep position are risk factors for sudden infant death syndrome and sudden unexpected infant death (SUID). The prevalence of surface sharing ranges from 34% to 64% among living infants and about 50% among SUID.
Compared with nonsurface sharing infants, infants who shared a surface at the time of death were more often younger, non-Hispanic Black, and publicly insured. However, most SUID, regardless of surface sharing status, were in unsafe sleep environments.
Sharing a sleep surface with an infant is discouraged because it increases the risk of sleep-related sudden unexpected infant death (SUID), including sudden infant death syndrome (SIDS), accidental suffocation and strangulation in bed, and other ill-defined and unknown causes.1,–6 SUID includes infants <1 year old who die suddenly and unexpectedly without an obvious cause before investigation7 and accounts for about 3400 deaths annually in the United States.8 In 2016 to 2017, 37% of US infants surface shared and 54% of infants in the SUID Case Registry were surface sharing at the time of death.6 Findings from a meta-analysis showed surface sharing was associated with an almost threefold risk of SIDS.1 Surface sharing is associated with an increased odds for both sleep-related suffocation and unexplained infant death (adjusted odds ratios: 2.5 [95% confidence interval (CI) 1.1–6.0] and 2.1 [95% CI 1.4–3.2] respectively).6 Surface sharing, especially on a couch or armchair, increases risk of unintentional suffocation by soft bedding, wedging or entrapment, and overlay.3,9,10 Moreover, surface sharing in combination with parental smoking and maternal alcohol or drug use greatly increases SIDS risk.11
In addition to surface sharing, independent risk factors for SIDS and other sleep-related infant deaths include nonsupine sleep position, an inclined or soft sleep surface, sleeping with soft, loose bedding, or objects, not breastfeeding, overheating, and prenatal or environmental exposure to tobacco smoke.4,–6 Among SUID with a complete investigation and documented sleep environment information, 98.5% occur in an unsafe sleep environment12; about half of SUID occur on a shared sleep surface.13,14
Understanding differences and similarities between SUID occurring on shared and nonshared sleep surfaces may inform safe infant sleep counseling, messaging, and future research. We describe characteristics and circumstances of SUID by surface sharing status, including infant demographics, birth characteristics, sleep environment, other characteristics, and SUID Case Registry Classification System category and suffocation mechanism. In addition, for surface-sharing SUID, we describe found location and person(s) sharing the sleep surface. Finally, because multiple births are overrepresented among SUID,15 we explore surface sharing and other sleep environment characteristics by plurality.
Methods
We used data from the Centers for Disease Control and Prevention’s SUID Case Registry (the Registry),16 a multijurisdictional, population-based surveillance system. The Registry builds on existing child death review programs and protocols and has been previously described.16,–18 Briefly, multidisciplinary child death review teams review and compile information on child deaths from multiple sources (eg, death certificates, autopsy reports, medical records) and make prevention recommendations based on their findings. Review information and recommendations are entered into the National Fatality Review-Case Reporting System (NFR-CRS).17
We studied 8192 SUID that occurred during 2011 to 2020 among residents of Registry jurisdictions including: Alaska; Arizona; San Francisco County, California; Colorado; Delaware; Georgia; Cook County, Illinois; Indiana; Kentucky; Louisiana; Maryland; Michigan; Minnesota; New Hampshire; New Jersey; New Mexico; Nevada; Pennsylvania; Tennessee; Utah; Tidewater Region of Virginia; Pierce County, Washington; and Wisconsin. SUID included deaths with any of the following causes reported on the death certificate: unknown, undetermined, SIDS, SUID, unintentional sleep-related asphyxia, suffocation, or strangulation, unspecified suffocation, cardiac or respiratory arrest without other well-defined causes, or ill-defined causes with potentially contributing unsafe sleep factors. Intentional homicides were excluded. We defined unsafe sleep as prone or side position, shared sleep surface, sleep surface other than a crib or bassinet, any bedding other than a fitted sheet, or soft objects in the sleep area.5 We excluded cases that had not undergone Registry data quality control procedures19 (n = 153) and those with missing or unknown information about surface sharing (n = 444). After exclusions, 7595 SUID remained.
Infant demographic and birth characteristics included age at death, sex, race and ethnicity, gestational age at birth, insurance type, and plurality. Sleep environment included infant’s found position and location, presence of soft bedding (excluding the sleep surface), and number of unsafe sleep factors other than surface sharing (including soft bedding, not in a crib, and non-supine position), and, among surface sharing infants, with whom the infant was surface sharing. Other characteristics included exposure to prenatal maternal cigarette smoking, ever breastfed, primary caregiver a parent, caregiver age, supervisor a parent, supervisor impaired by drugs or alcohol at time of death, open child protective services case for the infant, and having a crib or bassinet in the infant’s home. Variables are described in the NFR-CRS data dictionary.20
Infants were designated as “sharing” if they were sleeping with another person (ie, infant, child, or adult) or animal on any surface (eg, adult bed, crib, couch) at time of death. The NFR-CRS data dictionary guides child death review team members to ascertain infant race and ethnicity from the death certificate.20,21 We acknowledge that race and ethnicity are social constructs and not genetic or biological categories.22,23 We choose to report race and ethnicity because race and racism are embedded in our culture, societal structures, and systems supporting and affecting families and their understanding and implementation of safe sleep practices. We refer to cribs, bassinets, and portable cribs as “crib.” We quantified “unsafe sleep factors other than surface sharing” by combining multiple fields (ie, objects in the child’s sleep environment, found location, and found position). Because evidence about the safety of in-bed sleepers is limited, we grouped infants found in portable bassinets placed on an adult bed (n < 6) as “adult bed” for found location. Although “fed human milk” is more inclusive, we used “breastfed” for consistency with the NFR-CRS. “Primary caregiver” is the person who had responsibility for the infant’s care a majority of the time.20 “Supervisor” is the person who had responsibility for the infant’s care at time of death.20 “Parent” includes biological, adoptive, or step-parent.
The Registry Classification System category and suffocation mechanism were assigned by trained Registry staff using the SUID Case Registry Classification System and Algorithm.12,24 We collapsed the categories unexplained-incomplete case information and unexplained-no autopsy or death scene investigation into unexplained-incomplete information.
Among SUID, we calculated frequencies and percentages by surface sharing status for infant demographic and birth characteristics, sleep environment, other characteristics, Registry Classification System category, and, for SUID categorized as explained or possible suffocation, suffocation mechanism. We calculated χ-square tests of independence to determine if each variable was associated with surface sharing status. To limit the chance of erroneous associations, we excluded missing results from the χ-square analyses. Magnitude or direction of associations were not estimated. Most variables were significantly associated with surface sharing status (P < .05). In large study populations such as ours, statistical significance can emerge with small quantitative differences, complicating interpretation.25 Thus, we highlight clinically meaningful differences of at least 5 percentage points between sharing and nonsharing infants. We conducted analyses using SAS 9.3 (SAS Institute, Cary, NC). Each jurisdiction signed a data-use agreement allowing inclusion of de-identified, aggregated data.
Results
Of the 7595 SUID, 59.5% were sleep surface sharing and 40.5% were not at time of death (Table 1).
Infant and Other Characteristics Among Sudden Unexpected Infant Death by Surface Sharing Status, SUID Case Registry, 2011 to 2020
. | Percent Distribution by Surface Sharing Status . | . | ||||
---|---|---|---|---|---|---|
. | Sharing . | Nonsharing . | Pa . | |||
n | % | n | % | |||
Overall | 4520 | 59.5 | 3075 | 40.5 | ||
Infant demographic and birth characteristics | ||||||
Age in months | <.001 | |||||
0–3 | 3307 | 73.2 | 1744 | 56.7 | ||
4–6 | 903 | 20.0 | 940 | 30.6 | ||
7–<12 | 310 | 6.9 | 391 | 12.7 | ||
Infant sex | <.001 | |||||
Male | 2536 | 56.1 | 1844 | 60.0 | ||
Female | 1983 | 43.9 | 1228 | 39.9 | ||
Infant race and ethnicity | <.001 | |||||
Non-Hispanic American Indian/Alaska Native | 118 | 2.6 | 42 | 1.4 | ||
Non-Hispanic Asian | 25 | <1 | 39 | 1.3 | ||
Non-Hispanic Black | 1906 | 42.2 | 882 | 28.7 | ||
Non-Hispanic Native Hawaiian/Pacific Islander | 16 | <1 | 6 | <1 | ||
Non-Hispanic white | 1609 | 35.6 | 1422 | 46.2 | ||
Non-Hispanic multiple | 253 | 5.6 | 187 | 6.1 | ||
Hispanic | 532 | 11.8 | 456 | 14.8 | ||
Unknown | 60 | 1.3 | 40 | 1.3 | ||
Gestational age at birth | .004 | |||||
Preterm (≤33 wk) | 325 | 7.2 | 238 | 7.7 | ||
Late preterm (34–36 wk) | 732 | 16.2 | 405 | 13.2 | ||
Term (≥37 wk) | 3364 | 74.4 | 2358 | 76.7 | ||
Unknown | 77 | 1.7 | 54 | 1.8 | ||
Insurance type | <.001 | |||||
None | 76 | 1.7 | 64 | 2.1 | ||
Private | 521 | 11.5 | 610 | 19.8 | ||
Publicb | 3394 | 75.1 | 1976 | 64.3 | ||
Other or combination of public and private | 47 | 1.0 | 49 | 1.6 | ||
Unknown | 431 | 9.5 | 335 | 10.9 | ||
Plurality | <.001 | |||||
Multiple birth | 365 | 8.1 | 134 | 4.4 | ||
Singleton birth | 4113 | 91.0 | 2914 | 94.8 | ||
Unknown | 19 | <1 | 7 | <1 | ||
Sleep environment | ||||||
Infant’s found position | <.001 | |||||
Supine | 1858 | 41.1 | 1001 | 32.6 | ||
Prone | 1373 | 30.4 | 1521 | 49.5 | ||
Side | 729 | 16.1 | 373 | 12.1 | ||
Unknown | 507 | 11.2 | 158 | 5.1 | ||
Infant’s found location | <.001 | |||||
Crib, bassinet, or portable crib | 94 | 2.1 | 1594 | 51.8 | ||
Adult bed | 3422 | 75.7 | 678 | 22.0 | ||
Chair or couch | 710 | 15.7 | 134 | 4.4 | ||
Other | 284 | 6.4 | 654 | 21.3 | ||
Unknown | 10 | <1 | 14 | <1 | ||
Soft bedding in sleep environmentc | <.001 | |||||
Yes | 3089 | 68.3 | 2270 | 73.8 | ||
Not indicated | 1431 | 31.7 | 805 | 26.2 | ||
Number of unsafe sleep factors in addition to surface sharingd | n | % | n | % | <.001 | |
1 | 811 | 17.9 | 822 | 26.7 | ||
2 | 2277 | 50.4 | 1436 | 46.7 | ||
3 | 1414 | 31.3 | 647 | 21.0 | ||
Could not be determined | 18 | <1 | 159 | 5.2 | ||
Other characteristics | ||||||
Exposed to maternal cigarette smoking during pregnancy | <.001 | |||||
Yes | 1870 | 41.4 | 937 | 30.5 | ||
No | 2296 | 50.8 | 1901 | 61.8 | ||
Unknown | 307 | 6.8 | 196 | 6.4 | ||
Ever breastfed | .23 | |||||
Yes | 2425 | 53.7 | 1677 | 54.5 | ||
No | 1708 | 37.8 | 1110 | 36.1 | ||
Unknown | 347 | 7.7 | 259 | 8.4 | ||
Primary caregiver parente | <.001 | |||||
Yes | 4400 | 97.3 | 2920 | 95.0 | ||
No | 112 | 2.5 | 149 | 4.8 | ||
Unknown | — | — | 0 | 0.0 | ||
Caregiver age in years | .06 | |||||
≤19 | 425 | 9.4 | 267 | 8.7 | ||
20–24 | 1416 | 31.3 | 922 | 30.0 | ||
25–34 | 2052 | 45.4 | 1390 | 45.2 | ||
35+ | 469 | 10.4 | 345 | 11.2 | ||
Unknown | 123 | 2.7 | 114 | 3.7 | ||
Supervisor parente | <.001 | |||||
Yes | 3941 | 87.2 | 2228 | 72.5 | ||
No | 331 | 7.3 | 666 | 21.7 | ||
Unknown | — | — | — | — | ||
Supervisor impaired by drugs or alcohol at the time of the deathf | <.001 | |||||
Yes | 736 | 16.3 | 144 | 4.7 | ||
Not indicated | 3784 | 83.7 | 2931 | 95.3 | ||
Open child protective services case on the child at the time of the death | .005 | |||||
Yes | 485 | 10.7 | 329 | 10.7 | ||
No | 3705 | 82.0 | 2579 | 83.9 | ||
Unknown | 257 | 5.7 | 124 | 4.0 | ||
Crib or bassinet in the infant’s home | <.001 | |||||
Yes | 2561 | 56.7 | 2328 | 75.7 | ||
No | 824 | 18.2 | 313 | 10.2 | ||
Unknown | 1035 | 22.9 | 391 | 12.7 | ||
SUID case registry classification system category and suffocation mechanism | <.001 | |||||
Explained-suffocation with unsafe sleep factors | 881 | 19.5 | 677 | 22.0 | ||
Soft beddingg | 420 | 47.7 | 542 | 80.1 | ||
Wedgingg | 34 | 3.9 | 37 | 5.5 | ||
Overlayg | 250 | 28.4 | — | — | ||
Otherg or more than 1 indicated | 177 | 20.1 | 97 | 14.3 | ||
Unexplained-possible suffocation with unsafe sleep factors | 505 | 11.2 | 450 | 14.6 | ||
Unexplained-unsafe sleep factors | 2047 | 45.3 | 1250 | 40.7 | ||
Unexplained-no unsafe sleep factors | — | — | 70 | 2.3 | ||
Unexplained-incomplete informationh | 1083 | 24.0 | 628 | 20.4 |
. | Percent Distribution by Surface Sharing Status . | . | ||||
---|---|---|---|---|---|---|
. | Sharing . | Nonsharing . | Pa . | |||
n | % | n | % | |||
Overall | 4520 | 59.5 | 3075 | 40.5 | ||
Infant demographic and birth characteristics | ||||||
Age in months | <.001 | |||||
0–3 | 3307 | 73.2 | 1744 | 56.7 | ||
4–6 | 903 | 20.0 | 940 | 30.6 | ||
7–<12 | 310 | 6.9 | 391 | 12.7 | ||
Infant sex | <.001 | |||||
Male | 2536 | 56.1 | 1844 | 60.0 | ||
Female | 1983 | 43.9 | 1228 | 39.9 | ||
Infant race and ethnicity | <.001 | |||||
Non-Hispanic American Indian/Alaska Native | 118 | 2.6 | 42 | 1.4 | ||
Non-Hispanic Asian | 25 | <1 | 39 | 1.3 | ||
Non-Hispanic Black | 1906 | 42.2 | 882 | 28.7 | ||
Non-Hispanic Native Hawaiian/Pacific Islander | 16 | <1 | 6 | <1 | ||
Non-Hispanic white | 1609 | 35.6 | 1422 | 46.2 | ||
Non-Hispanic multiple | 253 | 5.6 | 187 | 6.1 | ||
Hispanic | 532 | 11.8 | 456 | 14.8 | ||
Unknown | 60 | 1.3 | 40 | 1.3 | ||
Gestational age at birth | .004 | |||||
Preterm (≤33 wk) | 325 | 7.2 | 238 | 7.7 | ||
Late preterm (34–36 wk) | 732 | 16.2 | 405 | 13.2 | ||
Term (≥37 wk) | 3364 | 74.4 | 2358 | 76.7 | ||
Unknown | 77 | 1.7 | 54 | 1.8 | ||
Insurance type | <.001 | |||||
None | 76 | 1.7 | 64 | 2.1 | ||
Private | 521 | 11.5 | 610 | 19.8 | ||
Publicb | 3394 | 75.1 | 1976 | 64.3 | ||
Other or combination of public and private | 47 | 1.0 | 49 | 1.6 | ||
Unknown | 431 | 9.5 | 335 | 10.9 | ||
Plurality | <.001 | |||||
Multiple birth | 365 | 8.1 | 134 | 4.4 | ||
Singleton birth | 4113 | 91.0 | 2914 | 94.8 | ||
Unknown | 19 | <1 | 7 | <1 | ||
Sleep environment | ||||||
Infant’s found position | <.001 | |||||
Supine | 1858 | 41.1 | 1001 | 32.6 | ||
Prone | 1373 | 30.4 | 1521 | 49.5 | ||
Side | 729 | 16.1 | 373 | 12.1 | ||
Unknown | 507 | 11.2 | 158 | 5.1 | ||
Infant’s found location | <.001 | |||||
Crib, bassinet, or portable crib | 94 | 2.1 | 1594 | 51.8 | ||
Adult bed | 3422 | 75.7 | 678 | 22.0 | ||
Chair or couch | 710 | 15.7 | 134 | 4.4 | ||
Other | 284 | 6.4 | 654 | 21.3 | ||
Unknown | 10 | <1 | 14 | <1 | ||
Soft bedding in sleep environmentc | <.001 | |||||
Yes | 3089 | 68.3 | 2270 | 73.8 | ||
Not indicated | 1431 | 31.7 | 805 | 26.2 | ||
Number of unsafe sleep factors in addition to surface sharingd | n | % | n | % | <.001 | |
1 | 811 | 17.9 | 822 | 26.7 | ||
2 | 2277 | 50.4 | 1436 | 46.7 | ||
3 | 1414 | 31.3 | 647 | 21.0 | ||
Could not be determined | 18 | <1 | 159 | 5.2 | ||
Other characteristics | ||||||
Exposed to maternal cigarette smoking during pregnancy | <.001 | |||||
Yes | 1870 | 41.4 | 937 | 30.5 | ||
No | 2296 | 50.8 | 1901 | 61.8 | ||
Unknown | 307 | 6.8 | 196 | 6.4 | ||
Ever breastfed | .23 | |||||
Yes | 2425 | 53.7 | 1677 | 54.5 | ||
No | 1708 | 37.8 | 1110 | 36.1 | ||
Unknown | 347 | 7.7 | 259 | 8.4 | ||
Primary caregiver parente | <.001 | |||||
Yes | 4400 | 97.3 | 2920 | 95.0 | ||
No | 112 | 2.5 | 149 | 4.8 | ||
Unknown | — | — | 0 | 0.0 | ||
Caregiver age in years | .06 | |||||
≤19 | 425 | 9.4 | 267 | 8.7 | ||
20–24 | 1416 | 31.3 | 922 | 30.0 | ||
25–34 | 2052 | 45.4 | 1390 | 45.2 | ||
35+ | 469 | 10.4 | 345 | 11.2 | ||
Unknown | 123 | 2.7 | 114 | 3.7 | ||
Supervisor parente | <.001 | |||||
Yes | 3941 | 87.2 | 2228 | 72.5 | ||
No | 331 | 7.3 | 666 | 21.7 | ||
Unknown | — | — | — | — | ||
Supervisor impaired by drugs or alcohol at the time of the deathf | <.001 | |||||
Yes | 736 | 16.3 | 144 | 4.7 | ||
Not indicated | 3784 | 83.7 | 2931 | 95.3 | ||
Open child protective services case on the child at the time of the death | .005 | |||||
Yes | 485 | 10.7 | 329 | 10.7 | ||
No | 3705 | 82.0 | 2579 | 83.9 | ||
Unknown | 257 | 5.7 | 124 | 4.0 | ||
Crib or bassinet in the infant’s home | <.001 | |||||
Yes | 2561 | 56.7 | 2328 | 75.7 | ||
No | 824 | 18.2 | 313 | 10.2 | ||
Unknown | 1035 | 22.9 | 391 | 12.7 | ||
SUID case registry classification system category and suffocation mechanism | <.001 | |||||
Explained-suffocation with unsafe sleep factors | 881 | 19.5 | 677 | 22.0 | ||
Soft beddingg | 420 | 47.7 | 542 | 80.1 | ||
Wedgingg | 34 | 3.9 | 37 | 5.5 | ||
Overlayg | 250 | 28.4 | — | — | ||
Otherg or more than 1 indicated | 177 | 20.1 | 97 | 14.3 | ||
Unexplained-possible suffocation with unsafe sleep factors | 505 | 11.2 | 450 | 14.6 | ||
Unexplained-unsafe sleep factors | 2047 | 45.3 | 1250 | 40.7 | ||
Unexplained-no unsafe sleep factors | — | — | 70 | 2.3 | ||
Unexplained-incomplete informationh | 1083 | 24.0 | 628 | 20.4 |
Cell counts between 0 and 6 are suppressed to maintain confidentiality.
A missing response indicates the question was skipped during data entry. An unknown response indicates the question was considered however the information necessary to answer the question was not available to anyone.19
Missing data were excluded from the χ-square analysis. Missing data were <3% for all variables, except for Supervisor Parent (Biological, Adoptive, or Step) with 5% missing data for sharing infants and 6% missing for nonsharing infants.
Includes Medicaid, State Plan, Indian Health Service.
Excludes the sleep surface (including noncrib mattress and cushion when incident sleep place is couch).
Factors include soft bedding; not in a crib, bassinet, or portable crib; and nonsupine position. Zero unsafe sleep factors could not be determined because the soft bedding variable does not distinguish between missing, unknown, and no.
Biological, adoptive, or step.
Assessment of supervisor drug or alcohol impairment status during the death scene investigation is not standard, and a test (eg, blood or breathalyzer) was not required for the supervisor to be documented as impaired.
The mechanisms are defined as follows: soft bedding is when the infant’s airway (nose and mouth) are obstructed by a soft item in the immediate sleep environment; wedging is when the infant’s airway (nose and mouth, neck or chest) is obstructed as a result of being stuck or trapped between inanimate objects; overlay is when the infant’s airway (nose and mouth, neck or chest) is obstructed by a person on top of or against the infant; other is when the infant’s airway is obstructed by something in the sleep environment other than soft bedding, overlay, or wedging (like a plastic bag).
Unexplained-incomplete case information and unexplained-no autopsy or death scene investigation categories are collapsed into unexplained-incomplete information.
Infant Demographic and Birth Characteristics
Infants aged 0 to 3 months made up the largest proportion of sharing (73.2%) and nonsharing infants (56.7%) (Table 1); however, a higher proportion of nonsharing infants were 4 to <12 months (43.3%) as compared with sharing infants (26.8%). Sharing infants were most commonly non-Hispanic Black (42.2%) and nonsharing infants were most commonly non-Hispanic white (46.2%). Publicly insured infants made up the largest proportion of sharing (75.1%) and nonsharing infants (64.3%); however, a higher proportion of nonsharing infants were privately insured (19.8%) as compared with sharing infants (11.5%). The differences between sharing and nonsharing infants in the distribution of infant sex, gestational age, and plurality were not clinically meaningful.
Sleep Environment
Sharing infants were most often supine (41.1%) and in an adult bed (75.7%); nonsharing infants were most often prone (49.5%) and in a crib (51.8%) (Table 1). Soft bedding in the sleep environment (excluding sleep surface) was common among sharing (68.3%) and nonsharing infants (73.8%). Sharing infants had a larger number of unsafe sleep factors in addition to surface sharing; specifically, 31.3% of sharing infants had all 3 unsafe sleep factors (soft or loose bedding or objects; not in a crib; prone or side position) as compared with 21.0% of nonsharing infants. At least 76% of SUID, regardless of sleep location, had multiple unsafe sleep factors present.
Other Characteristics
Exposure to prenatal maternal cigarette smoking was more common among sharing (41.4%) than nonsharing infants (30.5%). Being supervised by a parent at time of death was more common among sharing (87.2%) than nonsharing infants (72.5%). Having a supervisor who was impaired by drugs or alcohol was more common among sharing (16.3%) than nonsharing infants (4.7%). Not having a crib in the infant’s home was more common among sharing (18.6%) than nonsharing infants (10.2%) (Table 1). The differences between sharing and nonsharing infants in the distribution of ever breastfed, whether the primary caregiver was a parent, caregiver age, and having an open child protective services case were not clinically meaningful.
SUID Case Registry Classification System Category and Suffocation Mechanism
The difference between sharing and nonsharing infants with respect to classification system categories was not clinically meaningful. Among deaths categorized as explained-suffocation, the suffocation mechanism of soft bedding was the most common among sharing (47.7%) and nonsharing infants (80.1%). Of surface sharing infants classified as explained-suffocation, 28.4% were attributed to overlay.
Surface Sharing Location and Type of Person Sharing
Among surface-sharing SUID, 69.4% were sharing with 1 or more adult only, 21.9% with adults and other children, and 7.6% with other children only (Table 2). Among infants sharing with adults only, 75.2% were in an adult bed and 18.7% were on a couch or chair. Among infants sharing with other children only, 47.3% were in an adult bed, 26.9% were in a crib, and 13.0% were on a couch or chair. Among surface-sharing SUID, 51.6% were sharing with 1 other person, 34.9% with 2 other people, and 10.7% with ≥3 other people (not in table).
Found Location and Person(s) Sharing the Sleep Surface Among Surface Sharing Sudden Unexpected Infant Deaths, SUID Case Registry, 2011 to 2020
. | . | Person(s) Sharing Sleep Surface with Infant . | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
. | Total . | Adults Only . | Children Only . | Adults and Children . | Other Combinations of Adults, Children, and Petsa . | |||||
Found location . | n . | % . | n . | % . | n . | % . | n . | % . | n . | % . |
Crib, bassinette or portable crib | 94 | 2.1 | — | — | 91 | 26.9 | — | — | — | — |
Adult bed | 3355 | 75.8 | 2312 | 75.2 | 160 | 47.3 | 845 | 86.9 | 38 | 86.4 |
Couch or chair | 697 | 15.7 | 576 | 18.7 | 44 | 13.0 | 72 | 7.4 | 5 | 11.4 |
Other | 283 | 6.4 | — | — | 43 | 12.7 | 55 | 5.7 | — | — |
Overall total | 4429 | — | 3075 | 69.4 | 338 | 7.6 | 972 | 21.9 | 44 | 1.0 |
. | . | Person(s) Sharing Sleep Surface with Infant . | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
. | Total . | Adults Only . | Children Only . | Adults and Children . | Other Combinations of Adults, Children, and Petsa . | |||||
Found location . | n . | % . | n . | % . | n . | % . | n . | % . | n . | % . |
Crib, bassinette or portable crib | 94 | 2.1 | — | — | 91 | 26.9 | — | — | — | — |
Adult bed | 3355 | 75.8 | 2312 | 75.2 | 160 | 47.3 | 845 | 86.9 | 38 | 86.4 |
Couch or chair | 697 | 15.7 | 576 | 18.7 | 44 | 13.0 | 72 | 7.4 | 5 | 11.4 |
Other | 283 | 6.4 | — | — | 43 | 12.7 | 55 | 5.7 | — | — |
Overall total | 4429 | — | 3075 | 69.4 | 338 | 7.6 | 972 | 21.9 | 44 | 1.0 |
Select cells are suppressed to maintain confidentiality.
Two percent of total cases have missing or unknown information for incident sleep place and/or type of person sharing a sleep surface and were removed from this table.
A missing response indicates the question was skipped during data entry. An unknown response indicates the question was considered however the information necessary to answer the question was not available to anyone.19
Adults include infants who were sharing with 1 or more adults; children include infants who were sharing with 1 or more other children.
Equal to or less than 6 infants were surface sharing with just a pet.
Surface Sharing Characteristics Among Surface Sharing infants by Plurality
When comparing sharing and nonsharing infants, the difference in the plurality distribution was not clinically meaningful, however we found larger differences when comparing characteristics by plurality. Surface sharing was more common among multiples; of 499 multiples, 365 (73.1%) were surface sharing, and of 7027 singletons, 4113 (58.5%) were surface sharing (Table 1). Among surface-sharing SUID, multiples were sharing with adults only (23.8%), other children only (34.5%), or adults and other children (38.4%) (Table 3). Surface-sharing singletons were sharing with adults only (72.0%), other children only (5.1%), or adults and other children (20.1%). Infants found in an adult bed made up the largest proportion of surface-sharing multiples (61.1%) and surface-sharing singletons (77.0%). Being found in a crib was more common among surface-sharing multiples (22.2%) than surface-sharing singletons (<1% [n = 13]). The largest proportion of surface-sharing multiples were prone (38.9%), whereas the largest proportion of surface-sharing singletons were supine (41.8%). Finally, as compared with surface-sharing multiples, a larger proportion of surface-sharing singletons had more unsafe sleep factors in addition to surface sharing in their environment; specifically, 25.8% of surface-sharing multiples had all 3 unsafe sleep factors as compared with 31.8% of surface-sharing singletons. Among surface-sharing SUID, the difference between multiples and singletons with respect to having soft bedding in the sleep environment was not clinically meaningful.
Surface Sharing Characteristics Among Surface Sharing Sudden Expected Infant Deaths by Plurality, SUID Case Registry, 2011 to 2020
. | Multiple . | Singleton . | Pa . | ||
---|---|---|---|---|---|
. | n . | % . | n . | % . | . |
Overall | 365 | 8.2 | 4113 | 91.8 | |
Sharing withb | <.001 | ||||
Adults only | 87 | 23.8 | 2961 | 72.0 | |
Children only | 126 | 34.5 | 209 | 5.1 | |
Adults and children | 140 | 38.4 | 828 | 20.1 | |
Some combination of adults, children, and petsc | — | — | 40 | 1.0 | |
Found sleep location | <.001 | ||||
Crib, bassinet, or portable crib | 81 | 22.2 | 13 | <1 | |
Adult bed | 223 | 61.1 | 3166 | 77.0 | |
Chair or couch | 36 | 9.9 | 670 | 16.3 | |
Otherd | 23 | 6.3 | 257 | 6.2 | |
Unknown | — | — | 7 | <1 | |
Found position | .001 | ||||
Supine | 128 | 35.1 | 1720 | 41.8 | |
Prone | 142 | 38.9 | 1215 | 29.5 | |
Side | 49 | 13.4 | 675 | 16.4 | |
Unknown | 43 | 11.8 | 454 | 11.0 | |
Soft bedding in sleep environmente | .02 | ||||
Yes | 264 | 72.3 | 2804 | 68.2 | |
Not specified | 101 | 27.7 | 1309 | 31.8 | |
Number of unsafe sleep factorsf | <.001 | ||||
1 | 71 | 19.5 | 729 | 17.7 | |
2 | 192 | 52.6 | 2067 | 50.3 | |
3 | 94 | 25.8 | 1308 | 31.8 | |
Could not be determined | 8 | 2.2 | 9 | <1 |
. | Multiple . | Singleton . | Pa . | ||
---|---|---|---|---|---|
. | n . | % . | n . | % . | . |
Overall | 365 | 8.2 | 4113 | 91.8 | |
Sharing withb | <.001 | ||||
Adults only | 87 | 23.8 | 2961 | 72.0 | |
Children only | 126 | 34.5 | 209 | 5.1 | |
Adults and children | 140 | 38.4 | 828 | 20.1 | |
Some combination of adults, children, and petsc | — | — | 40 | 1.0 | |
Found sleep location | <.001 | ||||
Crib, bassinet, or portable crib | 81 | 22.2 | 13 | <1 | |
Adult bed | 223 | 61.1 | 3166 | 77.0 | |
Chair or couch | 36 | 9.9 | 670 | 16.3 | |
Otherd | 23 | 6.3 | 257 | 6.2 | |
Unknown | — | — | 7 | <1 | |
Found position | .001 | ||||
Supine | 128 | 35.1 | 1720 | 41.8 | |
Prone | 142 | 38.9 | 1215 | 29.5 | |
Side | 49 | 13.4 | 675 | 16.4 | |
Unknown | 43 | 11.8 | 454 | 11.0 | |
Soft bedding in sleep environmente | .02 | ||||
Yes | 264 | 72.3 | 2804 | 68.2 | |
Not specified | 101 | 27.7 | 1309 | 31.8 | |
Number of unsafe sleep factorsf | <.001 | ||||
1 | 71 | 19.5 | 729 | 17.7 | |
2 | 192 | 52.6 | 2067 | 50.3 | |
3 | 94 | 25.8 | 1308 | 31.8 | |
Could not be determined | 8 | 2.2 | 9 | <1 |
Cell counts between 0 and 6 are suppressed to maintain confidentiality.
One percent of total cases have missing or unknown information for plurality and were removed from this table.
Missing was <3% for all variables.
A missing response indicates the question was skipped during data entry. An unknown response indicates the question was considered however the information necessary to answer the question was not available to anyone.19
Missing data were excluded from the χ-square analysis.
Adults include infants who were sharing with 1 or more adults; children include infants who were sharing with 1 or more other children.
≤6 infants were surface sharing with just a pet.
Includes floor, car seat.
Excludes noncrib mattress; excludes cushion when incident sleep place is couch; these variables were only indicated as affirmative in the data as a result, it is not possible to discern between missing, unknown, and no.
Factors include soft bedding; not in a crib, bassinet, or portable crib; and prone or side position. Zero unsafe sleep factors could not be determined because the soft bedding variable does not distinguish between missing, unknown, and no.
Discussion
Overall, 59.5% of SUID were surface sharing when they died; 40.5% were not. These percentages are similar to other studies of SIDS and SUID (49.6% to 64.1%).6,13,14 Surface sharing among live infants ranges from 10.1% to 61.4% depending on study population.2,6,26,–30
Compared with nonsharing infants, sharing infants were more often 0 to 3 months old, non-Hispanic Black, publicly insured, found supine, in an adult bed or chair/couch, with a higher number of unsafe sleep factors (in addition to surface sharing) present, were exposed to prenatal maternal cigarette smoking, were supervised by a parent at time of death, or had a supervisor who was impaired by drugs or alcohol at time of death. Compared with sharing, nonsharing infants were more often >3 months old, non-Hispanic white, privately insured, found prone, in a crib, or had soft bedding in the sleep environment.
Many factors associated with surface sharing among living infants are similar to characteristics we described for surface-sharing SUID. Surface sharing among living infants has been shown to vary by measures of poverty and the following: non-Hispanic Black or racial or ethnic minorities, lower parental education, teenage motherhood, lower income, breastfeeding, maternal smoking, and residential mobility (ie, moved at least once since birth).26,–33
The prevalence of SUID exposed to prenatal maternal cigarette smoking (36.5% among SUID in the Registry; 41.4% among sharing and 30.5% among nonsharing infants) was higher than the 2020 US rate of 5.5% among all births.34 Maternal smoking is a known risk factor for SIDS and SUID, and the risk of SIDS associated with surface sharing increases when 1 or both parents smoke or when the infant’s mother smoked during pregnancy.4,–6,35,–39 Surface sharing-related risk for SIDS increases 10-fold when surface sharing occurs with a current smoker or if the pregnant parent smoked during pregnancy.1,4,5,40,–44
Breastfeeding is a protective factor against SIDS and mother-infant surface sharing has been encouraged by some to facilitate breastfeeding,4,45,–47 despite American Academy Pediatrics (AAP)’s recommendation of nonshared infant sleep surfaces.1,–5,48 Among SUID in our study, there was <5% difference between sharing and nonsharing in the proportion of infants ever breastfed. Interpretation of this finding is limited because “ever breastfed” is typically abstracted from the birth certificate, which only documents breastfeeding initiation, and not exclusivity and duration.49
Multiple births are more likely to be preterm or have low birth weight, increasing the risk of SIDS.4 AAP recommends multiples sleep on separate surfaces.50 However, we found among SUID, surface sharing was more common among multiples than singletons, most often in an adult bed followed by the same crib. Other studies have similarly found multiples more commonly surface share than singletons.51,52 Parents with multiples cite space and financial constraints as reasons for placing their infants to sleep on a shared surface.53 This finding has important implications because multiples are over-represented among SUID, both in our study and US death data. During 2011 to 2020, 5.9% of US SUID were multiples,15 whereas 3.4% of US births were multiples.34
Although some characteristics were more common among surface sharing or nonsharing infants, and future research may be necessary to identify the etiology of those differences, most SUID had at least 1 unsafe factor in their sleep environment regardless of surface sharing status. Surface sharing in the absence of other unsafe sleep factors was rare. Furthermore, nonsharing infants were commonly in both an unsafe sleep position and with soft bedding in their sleep environment. Thus, surface-sharing in and of itself may not be what caregiver education should focus on. These results support efforts to provide comprehensive safe sleep messaging and not focus solely on not surface sharing, for all families at every encounter.
Clinicians can use evidence from this and previous studies to shape conversations on safe sleep guidance, including understanding motivations for surface sharing2,54,55 and the impact of modeling behavior and giving advice to encourage safe sleep practices.26,56,57 Previously reported reasons for surface sharing included breastfeeding, facilitating better sleep for the infant or mother, calming a fussy infant, convenience, keeping a close watch over the infant, and protection from environmental dangers.2,54,55 African American mothers reported privacy, concern about becoming accustomed to always sleeping in the parents’ bed, and fear about suffocation as reasons for not surface sharing.55
Most infants in our study were being cared for by a parent when they died. This finding is relevant because parental practices may be influenced by practices observed in the hospital56 or advice from healthcare providers (eg, safe sleep recommendations or smoking cessation)26,57 can impact behavior. Thus, it is critical for healthcare providers to appropriately model and discuss planned and actual infant sleep practices during prenatal visits, birth hospitalization, and postnatal and well-child visits. Engaging parents in discussions about their sleep practices and helping them make decisions to address their concerns and also reduce SUID risk is valuable.
As surface sharing infants more commonly did not have a crib in the home and more often relied on public insurance, when appropriate, pediatricians and other healthcare providers can consider connecting caregivers with free crib distribution programs. These programs can improve safe sleep knowledge and practice.58,–60 Additional research is needed to understand how socioeconomic and other social determinants of health influence infant sleep environments and how best to support families in practicing safe infant sleep.61,–63
Our analysis has several limitations. First, sleep environment data depends on availability and accuracy of information documented during death investigation, which relies on witness reports of an often chaotic scene.64 Surface sharing and other unsafe sleep practices may be underreported because of caregiver awareness of safe sleep recommendations and social desirability bias.5 Caregiver reasons for surface sharing were not available. Second, varying data collection methods and bias may influence information documented in the Registry.65 For example, there was no standard assessment (eg, blood or breathalyzer) or documentation of drug and alcohol impairment of infant supervisors. Therefore, bias is possible in drug screening if, for example, low-income or nonwhite caregivers were differentially screened for substance use.66,67 Third, our study population was limited to 23 US states and jurisdictions, which may limit generalizability. However, the Registry represents a third of US SUID and has wide geographic diversity. Fourth, cautious interpretation of crib availability is warranted because of a high number of unknown responses. Finally, we were unable to determine risk because the Registry includes only infant deaths and thus, we lacked an appropriate comparison group (eg, living infants).
Conclusions
Characteristics of surface sharing and nonsharing infants among SUID varied by age at death, race and ethnicity, infant insurance type, and presence of unsafe sleep factors. However, most SUID had multiple unsafe sleep factors present regardless of sharing status. The safest place for an infant to sleep is supine, on a nonshared sleep surface, in a crib or bassinet, and without soft bedding.5 Supporting families in following the AAP recommendations for reducing sleep-related infant deaths5 is complex. Our findings support comprehensive safe sleep counseling for every family at every encounter beyond just asking where an infant is sleeping.
Acknowledgments
We thank SUID Case Registry awardees (cooperative agreements DP09-904, DP12-1202, DP14-1403, DP15-1506, DP18-1806) in Alaska; Arizona; San Francisco County, California; Colorado; Delaware; Georgia; Cook County, Illinois; Indiana; Kentucky; Louisiana; Maryland; Michigan; Minnesota; New Hampshire; New Jersey; New Mexico; Nevada; Pennsylvania; Tennessee; Utah; Tidewater Region of Virginia; Pierce County, Washington; and Wisconsin. We thank the leadership and data team Abby Collier, Heather Dykstra, and Esther Shaw, at the National Center for Fatality Review and Prevention for their support in preparing data from the NFR-CRS. We thank the Health Resources and Services Administration Maternal and Child Health Bureau for their longstanding support of the child death review programs.
Ms Erck Lambert conceptualized and designed the study, conducted all analyses, and drafted the initial manuscript; Drs Shapiro-Mendoza, Hauck, and Parks, Ms Faulkner, and Ms Cottengim conceptualized and designed the study; and all authors critically reviewed and revised the manuscript, approved the final manuscript as submitted, and agree to be accountable for all aspects of the work.
DISCLAIMER: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
FUNDING: No external funding.
CONFLICT OF INTEREST DISCLOSURES: The authors have no potential conflicts of interest to disclose.
Comments
SUID and SIDS are not interchangeable
We have found similar results in our research using of Connecticut Child Fatality Review data. The majority of sudden unexpected infant deaths (SUIDs) we have reviewed over the past five years show that most (68.5%) infants were found unresponsive in a non-recommended sleep location; 57.3% were supine. Because we reviewed all scene re-enactments, we found that 21.3% had evidence of airway obstruction from the sleep environment. Most (68.5%) were in the first sleep environment, and 31.5% were in the second sleep environment. Only 3.5% were supine in a separate, recommended, uncluttered infant sleep surface at either the first or second sleep environment. Mothers were predominantly responsible for the last sleeping environment; however, in 36.5% of cases, it was another caregiver (e.g., father, grandmother, babysitter). Thus, most infant awakenings do not often lead to the child being moved to a second sleep environment, as the majority of SUIDs involved unsafe first infant sleeping environments. The majority of infants were found supine and airway obstruction was documented in 1 in 5 cases. In safe sleep education, strategies should include all caregivers, especially fathers and grandparents. Our work reinforces the importance of scene re-enactments in death investigation and further demonstrates the role that the sleep environment plays in infant deaths.
Additionally, the authors seem to use sudden infant death syndrome (SIDS) and SUID interchangeably and refer to SIDS as a subset of SUID. From a forensic pathology and cause of death point of view, this is inaccurate. In the article, the authors speak of SIDS having a threefold increased risk when there is surface sharing. By the definitions laid out in the textbook, “Unexplained Pediatric Deaths” by the editors, Drs. Bundock and Corey, if there is co-sleeping involved, the cause of death cannot be SIDS. Additionally, if the child is found on anything other than a firm, flat, separate sleeping surface that is without pillows, blankets, and the like, the cause of death cannot be SIDS.
Forensic pathologists coined SUID to separate these cases from SIDS. The assertion in the pediatric realm that the terms SIDS and SUID are interchangeable or that "SUID is the new SIDS" is incorrect because, in forensic pathology, they are two definitively different terms that make an essential distinction in the classification of the cause of death.
Thank you for considering our comments.
Kirsten Bechtel MD
Julie R. Gaither PhD
Yale School of Medicine
Gregory Vincent MD
Office of the Chief Medical Examiner, Connecticut
References
Erck Lambert AB, Shapiro-Mendoza CK, Parks SE, Cottengim C, Faulkner M, Hauck FR. Characteristics of Sudden Unexpected Infant Deaths on Shared and Nonshared Sleep Surfaces. Pediatrics. 2024 Mar 1;153(3):e2023061984. doi: 10.1542/peds.2023-061984. PMID: 38374785.
Bundock EA, Corey TS, Andrew TA, et al., editors. Unexplained Pediatric Deaths: Investigation, Certification, and Family Needs [Internet]. San Diego (CA): Academic Forensic Pathology International; 2019. Available from: https://www.ncbi.nlm.nih.gov/books/NBK577018/