PEDIATRICS Vol. 121 No. 6 June 2008, pp. e1478-e1483 (doi:10.1542/10.1542/peds.2007-2749)
ARTICLE |
Head Covering and the Risk for SIDS: Findings From the New Zealand and German SIDS Case-Control Studies
a Department of Paediatrics, University of Auckland, Auckland, New Zealand
b Department of Obstetrics and Gynaecology, University of Auckland, Auckland, New Zealand
c Institute of Legal Medicine, University of Duisburg, Essen, Germany
d Institute of Legal Medicine, University of Münster, Münster, Germany
g Department of Medical Informatics and Biomathematics, University of Münster, Münster, Germany
e Department of Pediatrics, University of Magdeburg, Magdeburg, Germany
f Institute of Child Life and Health, University of Bristol, Bristol, United Kingdom
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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OBJECTIVES. The aim of this investigation was to identify risk factors for being found with the head covered in sudden infant death syndrome cases and determine whether head covering was likely to be an agonal event or potentially part of the causal pathway in some cases. By using the data from 2 sudden infant death syndrome case-control studies, consistency of the findings could be assessed.
METHODS. Two case-control studies were assessed: (1) the New Zealand Cot Death Study (1987–1990, 393 sudden infant death syndrome cases) and (2) a German SIDS case-control study (1998–2001, 333 sudden infant death syndrome cases).
RESULTS. The proportion of sudden infant death syndrome cases in which infants were found with their head covered was 15.6% in the New Zealand study and 28.1% in the German study. Being found with head covering was associated with older infant age. In both studies, being found with head covering was associated with being very sweaty when found. Head covering was also associated with the incidence and severity of thymic petechiae in both studies. Both the position in which the child was placed to sleep and the position in which the child was found were not associated with head covering.
CONCLUSIONS. The finding that sudden infant death syndrome cases in which infants were found with their heads covered were often very sweaty suggests that head covering was not an agonal event and that it preceded the death and may have been causally related to the death. Infants who were found with their head covered were older, which probably reflects motor development.
Key Words: sudden infant death • head covering • sweating • thymic petechiae
Abbreviations: SIDS—sudden infant death syndrome • GeSID—German SIDS case-control study • CI—confidence interval • OR—odds ratio
Reports of infants' being found dead with their head covered by blankets and other forms of bedding have been reported in many different studies, and the prevalence varies from 12%1 to 48%.2 The pooled prevalence in sudden infant death syndrome (SIDS) victims is 24.6% (95% confidence interval [CI]: 22.3%–27.1%; Blair et al, unpublished meta-analysis). Most studies reported a prevalence of 
20%.3–5 In case-control studies, it is uncommon for the control (alive) infant to be found with his or her head covered at the end of the reference sleep, which results in head covering's being associated with a very high relative risk for SIDS. The United Kingdom Department of Health's "Reduce the Risk of Cot Death" pamphlet advises avoidance of head covering as part of their SIDS prevention strategy, by including the advice "Feet to Foot," by which they mean place the infant's feet at the foot of the cot, thus preventing the infant from sliding down under the bedding.6 The German Pediatric Association advises the use of an infant sleeping bag to avoid head covering and advises against additional bedding; however, being found with the head covered occurs at some time during the infant's life in 30% of infants who do not die,7,8 suggesting that the majority of episodes of head covering do not result in death. Thus, head covering may be an agonal event and not related to the cause of death.
The aim of this investigation was to identify risk factors for head covering in SIDS cases and determine whether head covering was likely to be an agonal event or potentially part of the causal pathway in some cases. By using the data from 2 SIDS case-control studies, we could assess consistency of the findings.
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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New Zealand Cot Death Study
The New Zealand Cot Death Study was a nationwide case-control study from November 1987 to October 1990 that examined risk factors for SIDS.9,10 Most of the data collected preceded the SIDS Prevention Campaign ("Back to Sleep"). There were 485 SIDS cases. Autopsies were conducted in 474 (97.7%) of the SIDS cases. Obstetric records were examined in 465 (95.9%), and 393 (81.0%) parents were interviewed. Information on head covering was available for 385 of the SIDS cases. The SIDS victims were compared with 1800 randomly sampled control subjects, who were representative of all births in the study regions during the same time period; however, the New Zealand study did not collect information from the control families about being found with the head covered for the nominated (reference) sleep. Thus, only cases were considered in this analysis.
The German SIDS Case-Control Study
The German SIDS case-control study (GeSID) was a large population-based study of infants who died of SIDS between 1 week and 1 year of age (postperinatal deaths) in the period November 1998 to October 2001, which was after the "Back to Sleep" campaign.11,12 All infants were autopsied by forensic pathologists according to a standardized autopsy protocol. There were 404 SIDS cases, and the parents of 333 (82.4%) of these infants were interviewed. Information on head covering was available for 327 cases. GeSID did collect this information from parents of control subjects, but only 10 interviewees reported that the infant's head was covered when found; the risk for SIDS associated with head covering was 44.5 (95% CI: 19.5–101.7). The small number of control subjects with head covering precludes additional analysis, so subsequent analyses were of the SIDS-case infants only.
Explanatory Variables
Although the questionnaires were conducted in different languages, the following explanatory variables were common to both studies and were examined in this report: maternal factors (maternal age, marital status, smoking in pregnancy, and parity), infant factors (gender, ethnicity [European versus non-European], birth weight, and gestation), and postnatal factors (age; time found dead; season; breastfeeding [New Zealand study: breastfeeding ever; GeSID: breastfeeding for the first 2 weeks of life]; and in the last sleep: position placed to sleep, position found, bed sharing, pacifier use, pillow use, duvet use, and sleeping in the parental bedroom). Duvet use in New Zealand was recorded as yes or no. In GeSID, duvet use was classified as heavy duvet, light duvet, and all other bedding. For comparison with the New Zealand study, heavy duvet use was compared with the combination of light duvet and all other bedding. The New Zealand study also examined whether the infant was tucked in firmly.
In the New Zealand study, the families were asked whether the infant was found "drenched in sweat." The GeSID question that we consider similar was "found with bedding and the clothing of the infant moist from sweat." These questions are subsequently referred to as "found very sweaty."
In the New Zealand study, petechial hemorrhages were recorded in 3 categories: nil, few, and many at 3 sites (the visceral pleura, the thymic capsule, and epicardium).13 In the GeSID study, petechial hemorrhages were recorded in 4 categories: nil, few, moderate, and many at several sites (left and right visceral and parietal pleura, thymus, pericardium, and epicardium). There was close agreement for the amount of petechial hemorrhages in the left and right visceral pleura (weighted 
= 0.95) and for the left and right parietal pleura (weighted = 0.91). Where there was a difference, we took the greater amount of petechial hemorrhage to represent that case.
Statistical Analysis
Odds ratios (ORs) were estimated by using logistic regression in SAS 9.1 (SAS Institute, Inc, Cary, NC). Multivariable analysis was conducted by controlling for all variables found to be significant at the 10% level in the univariate analyses in either the New Zealand or the GeSID study. Multivariable analysis by using petechial hemorrhages as the outcome was conducted using polytomous logistic regression in proc logistic of SAS 9.1. The multivariable model controlled for variables that were shown to be related to head covering.
Ethical Approval
Ethical approval for these 2 studies was obtained as previously described.9–12
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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There were 60 (15.6%) SIDS victims found with their head covered in the New Zealand study and 92 (28.1%) in GeSID (
2 = 16.58, P < .0001). Subsequent analyses were conducted separately. In both studies, the median age of infants who were found with their head covered was greater than those whose head was not covered (New Zealand: 19.4 weeks [interquartile range: 12.9–27.4) vs 11.3 [IQR: 8.0–16.1; P < .0001); GeSID: 30.5 weeks [IQR: 18.5–39.0] vs 14.0 [IQR: 9.0–22.0; P < .0001]). In both studies, being found very sweaty was associated with head covering (New Zealand: adjusted OR: 7.20 [95% CI: 3.54–14.65]; GeSID: adjusted OR: 4.79 [95% CI: 2.19–10.50]; Table 1).
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In the New Zealand study, bed sharing was associated with a reduced risk for being found with head covered, and this remained significant after adjustment for potential confounders. In the GeSID, bed sharing was also associated with a reduced risk for head covering (OR: 0.46 [95% CI: 0.21–1.03]) at the 6% significance level, but after adjustment for potential confounders, bed sharing was not significant. In both studies, sleeping in their own bedroom or with siblings was associated with head covering compared with sleeping in the parental bedroom, but in neither study was this significant after adjustment for confounders.
Being placed prone to sleep was associated with a reduced risk for head covering in the GeSID study at the 5% significance level but not in the New Zealand study. In the multivariable analysis, sleep position was not significantly associated with head covering. Position found was not associated with head covering in either study (New Zealand study: OR: 0.72 [95% CI: 0.42–1.25]; GeSID study: OR: 1.38 [95% CI: 0.80–2.41]). Other risk factors for SIDS (maternal smoking, not breastfeeding, not using pacifier, and sociodemographic risk factors) were not associated with head covering in either study (Table 2).
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Duvet use was associated with an increased risk for head covering in GeSID but not in the New Zealand study, although the finding was in the same direction. In GeSID, heavy duvets were associated with an increased risk for head covering (adjusted OR: 2.94 [95% CI: 1.56–5.52]) compared with all other bedding. In the New Zealand study, being firmly tucked in was associated with a reduced risk for head covering but not significantly so (OR: 0.68 [95% CI: 0.34–1.33]; not examined in GeSID study).
The New Zealand findings for the relationship between petechial hemorrhages and head covering have been reported previously13 but are reproduced here for ease of comparison with GeSID (Table 3) . In both studies, head covering was associated with thymic petechiae, whereas there was no association with visceral pleura petechiae. Head covering was associated with epicardial petechiae in the New Zealand study but not in GeSID. Head covering was associated with fewer petechial hemorrhages in the parietal pleura in the GeSID study (not examined in the New Zealand study). After controlling for factors related to head covering, there continued to be statistically significant relationships between head covering and the presence of petechiae in the thymus (both studies) and epicardium (New Zealand study) and fewer petechiae in parietal pleura (GeSID study).
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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The proportion of SIDS victims found dead with their head covered was 15.6% in the New Zealand study and 28.1% in GeSID. This difference is statistically significant, but the prevalences of head covering were within the range reported from other studies.3–5The reason for this difference is not apparent; however, the prevalence of head covering in the GeSID study was less than that reported from previous German studies (44% and 37%),14,15 whereas the prevalence of head covering in the New Zealand study was similar to that reported from a previous New Zealand study.1
Infants who died and were found with their head covered were older than those found without their head covered. This probably reflects their greater motor development, which may result in their moving under the bedding or kicking the bedding over their head.
Position placed to sleep or position found was not associated with head covering. It has been suggested that older infants who are placed prone might be more likely to move backward and under the bedding. Ponsonby et al16 suggested that infants who are placed supine might kick duvets over their head. Skadberg and Markestad17 reported that infants who are aged 2.5 and 5 months and sleep prone are less able to remove the bedding from the head on awakening compared with those who sleep supine. Neither suggestion can be supported by our analyses. Sleeping sacks/bags have been recommended to prevent the head from being covered by bedding.18 We were not able to confirm this by our results, because this type of bedding was used infrequently at the time of these studies. Neither study asked about position in the cot, so we cannot comment on whether the "Feet to Foot" recommendation prevents head covering. The prone sleeping position was less common in Germany because that study was done at a time when the prone position was a well-established risk factor for SIDS, whereas the New Zealand study was done before the "Back to Sleep" campaign.
Duvets were associated with head covering in the GeSID study after adjustment for confounders. Duvet was not associated with head covering in the New Zealand study, although the direction of the finding was similar. This may reflect differences between the types of duvets used in each country. In Germany, the duvet is an eiderdown, whereas in New Zealand, duvets are usually thinner and filled with a synthetic fiber. We hypothesized that being tucked in firmly would reduce the risk for head covering by preventing the bedding from being kicked up over the head, but this was not seen.
In the New Zealand study but not GeSID, bed sharing was associated with a decreased risk for being found with the head covered. Head covering during co-sleeping is common. Baddock et al19 reported that there were 102 head-covering episodes for the 22 infants studied. The majority of head covering during co-sleeping was by inadvertent movements by the adults as they changed position during sleep. Sixty-eight percent of head uncovering was facilitated by the mother, and half of these events were prompted by the infant. It is possible that for SIDS cases, when mothers wake up, they uncover the infant's head. They then discover that the infant has died, thus reporting the low incidence of head covering while bed sharing.
There has been debate as to whether head covering is a cause of SIDS or an agonal event. Head covering might result in rebreathing of expired gases, resulting in hypoxia and hypercapnea. Because the face is an important body surface for heat loss, head covering might result in thermal stress.20 Franco et al20,21 reported that infants with their head covered had a decreased arousal and a higher rectal temperature as well as a higher pericephalic temperature. The observation in both studies that head covering was associated with being found very sweaty provides support for a thermal mechanism. Sweating to a degree that resulted in "drenched in sweat" or "moist bedding" suggests that the head covering must have occurred before death and thus is not an agonal event; this was also reported in a previous study by Kleemann et al.14
In both studies (after controlling for confounders), associations were shown between head covering and a greater incidence and severity of petechial hemorrhages in the thymus. The New Zealand study also showed an association between head covering and the incidence and severity of pericardial petechiae, whereas the GeSID study found an inverse association with petechiae in the parietal pleura (not examined in the New Zealand study). Neither study showed an association between head covering and visceral pleural petechiae. It is difficult to draw additional conclusions from these associations, largely because of uncertainty about the pathogenesis of petechial hemorrhages in SIDS.13 Intrathoracic petechiae are found in deaths from many causes, but the number and prominence of petechiae in SIDS led Beckwith22 to conclude: "As a group, SIDS victims seem to have experienced a final episode that either in nature or degree is relatively unique and is not experienced by the majority of dying humans." Therefore, the association of petechial hemorrhages with head covering is an indication that the terminal episode differs between those who die with or without their head covered. The additional association of head covering with heavy sweating during the final episode suggested that hyperthermia might have caused the increased numbers of petechiae,23 but, in the New Zealand study, we previously reported that excessive sweating and petechial incidence were not associated.13
Head covering and other factors that are associated with the incidence of petechiae at the 3 intrathoracic sites vary, and there is no ready explanation for this on the basis of previous suggestions about the pathogenesis of petechiae. It is unclear why suggested systemic factors such as hypoxia, hyperthermia, and heart failure or superimposed intrathoracic factors such as barotrauma during forced expiration against an obstructed airway24 or the mechanical effects on small vessels of respiratory and cardiac movements25 should have different effects at each anatomic site.
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CONCLUSIONS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Head covering precedes the death and is not an agonal event and is causally related to SIDS. This supports the recommendation to avoid head covering as part of the SIDS prevention strategies. Evidence on how best to achieve this is urgently required.
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ACKNOWLEDGMENTS |
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The German Federal Ministry for Science and Education supported the GeSID study on sudden infant death syndrome from 1998 to 2003, and the Health Research Council of New Zealand and the Hawkes Bay Medical Research Foundation funded the New Zealand study. Professor Mitchell and Dr Thompson are supported by the Child Health Research Foundation, New Zealand.
The GeSID study group included P. Bach, B. Bockholt, M. Bohnert, U. Cremer, U. Deml, A. Freislederer, S. Heide, W. Huckenbeck, K. Jachau, H.-J. Kaatsch, A. Klein, W.J. Kleemann, K.-P. Larsch, A. Fiegut, D. Fischer, W. Leukel, C. Ortmann, E. Rauch, W. Paulus, R. Penning, F. Rublack, C. Sauerland, M. Schlaud, B. Schmidt, J. Sperhake, G. Zimmer, and R. Zweihoff. Other members of the New Zealand Cot Death Study Group were E.M. Allen, D.M.J. Barry, R.P.K. Ford, I.B. Hassall, A.P. Roberts, R. Scragg, A.W. Stewart, B.J. Taylor, and S. Williams.
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FOOTNOTES |
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Accepted Jan 2, 2008.
Address correspondence to Edwin A. Mitchell, DSc, University of Auckland, Department of Paediatrics, Private Bag 92019, Auckland, New Zealand. E-mail: e.mitchell{at}auckland.ac.nz
The authors have indicated they have no financial relationships relevant to this article to disclose.
| What's Known on This Subject Approximately 25% of infants with SIDS are found dead with their head covered by bedding. It is uncertain whether head covering is an agonal event or is related to the cause of death.
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| What This Study Adds Infants who were found dead with their head covered were often very sweaty, indicating that head covering was not an agonal event and that it preceded the death. Infants who were found with their head covered were older, which probably reflects motor development.
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PEDIATRICS (ISSN 1098-4275). ©2008 by the American Academy of Pediatrics
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