Several newspapers have reported on research into cot deaths, or sudden infant death syndrome (SIDS). The Daily Telegraph and The Times report that half of cot deaths “happen when babies are sleeping with their parents”, while the Daily Express says that one in four cot deaths is linked to “swaddling of babies”.
This study investigated the circumstances surrounding cot deaths that occurred in the south-west region of the UK over a four-year period, comparing them to a group of healthy babies.
Cot death is a rare occurrence, and because of this, the sample sizes in this study were small. As such, it cannot give reliable estimates of risk. However, the findings confirm some known associations and highlight the possible importance of others. For instance, more than half of SIDS cases had been "co-sleeping" (defined by the researchers as sharing a bed or a sofa with a parent or another child). The researchers say that much of this risk could be explained by co-sleeping with a parent following parental drug or alcohol use, or sleeping with a parent on a sofa. They do not provide a separate estimate of the risk of SIDS while sharing a bed with a parent in the absence of these and other risk factors.
Swaddling (wrapping the baby up in blankets), using a pillow, smoking during pregnancy, premature babies, sleeping on the front rather than the back and general health at time of death were also associated with increased risk of cot death.
Where did the story come from?
The research was carried out by Peter Blair and colleagues from the Universities of Bristol and Warwick. It was published in the British Medical Journal and funding was provided by grants from the Foundation for the Study of Infant Deaths (FSID), Babes in Arms and the charitable trusts of University Hospitals Bristol.
What kind of scientific study was this?
Cot death or sudden infant death syndrome (SIDS) is the sudden unexpected death of an apparently healthy baby aged from newborn to two years old. There have been several campaigns aimed at educating the public about the risk factors for SIDS.
This case-control study investigated the factors associated with cot death from birth to age two, looking for any previously unidentified risk factors, and the specific circumstances in which SIDS occurs during co-sleeping (infant sharing the same bed or sofa with an adult or child).
The study was carried out between January 2003 and December 2006. This involved comparing the circumstances of all cases of SIDS in the south-west of England to two control groups of healthy babies.
For SIDS cases, a full history of the death was taken from the parents by a paediatrician, health visitor and member of the police child-protection team, along with the usual protocols for care of the bereaved family and investigation of the circumstances surrounding death. The families were asked several days after the death if they would consider being included in the study, and the families who agreed to take part were visited by the researchers within two weeks to complete a further detailed questionnaire. The 80 cases in the study all had no identified cause of death and so met the definition of cot death/SIDS.
The cases were compared to two control groups that had been identified from a maternity database. Controls were followed up to the age of eight months using a number of postal questionnaires.
To investigate whether some of the risk factors might be related to socioeconomic deprivation, one of the control groups consisted of 82 children considered to be at the highest risk of cot death (risk factors included: a young mother, social deprivation, mothers who smoked and had a number of other children). The other control group was a random sample of 87 children considered to be at normal risk matched to the SIDS cases by mothers’ social class.
Some of the control families were also interviewed at home using a similar questionnaire to the one given to the bereaved families. The parents were also asked to identify a particular time during the past 24 hours that their baby had been asleep. In their analyses, the researchers adjusted for the characteristics that were different between the SIDS and control groups to ensure that they were as balanced as possible on age and on the time of the sleep event being investigated.
The researchers explored whether there were links between cot death and particular risk factors including:
- Co-sleeping with either another adult or a child.
- Prescribed drugs or illegal drugs used either medically or recreationally by the parents/carers.
- High alcohol intake by the parents.
What were the results of the study?
There were 155 cot deaths out of 184,800 births in the south-west of England during the study period (0.084% of births). However, a cause of death was found for 67 of these, leaving 90 defined cot deaths (a rate of 0.49 per 1,000 live births).
The average (median) age at the time of infant death was 66 days. More than half of the SIDS cases (54%) had been co-sleeping (in a bed or on the sofa) with a parent, compared to only 20% in both control groups (high and normal risk).
In many of the SIDS cases who had died during co-sleeping, there were several other risk factors present, which the researchers say could explain much of the increased risk. For instance, in 31% of these cases, the parents had recently used either drugs or alcohol (compared to 3% of the normal risk controls). For 17% of these cases, babies were sleeping with their parent on the sofa (compared to 1% of the normal risk controls).
Other factors that had significantly higher prevalence in the cot death group compared to the normal controls were:
- 21% of the SIDS cases had died while using a pillow, compared to 3% of controls.
- 24% were swaddled, compared to 6% of controls.
- 60% of the mothers of SIDS cases smoked during pregnancy, compared to 14% of controls.
- 26% of the SIDS cases were premature, compared to 5% of controls.
- 28% of the SIDS cases were in fair or poor health for the last sleep, compared to 6% of controls.
- 29% of the SIDS cases slept on their fronts rather than their back, compared to 10% of controls.
No significant relationships were found between covering the infant’s head during sleep, exposure to tobacco smoke in the house, using a dummy or sleeping on their side.
What interpretations did the researchers draw from these results?
The researchers say that many of the infants who died of cot death had co-slept, in addition to being exposed to other hazards such as parental use of alcohol or drugs or sleeping on a sofa. They say that specific advice needs to be given about these factors. For example they say, “It is not enough to advise against co-sleeping on a sofa; health professionals must advise parents to avoid putting themselves in the position where this could happen.”
What does the NHS Knowledge Service make of this study?
There is no single clearly established cause for cot death, but there are numerous factors associated with increased risk. This study found significant associations with some factors, most notably co-sleeping with a parent. A large proportion of this co-sleeping risk was attributed to sleeping with a parent on a sofa, or the parent’s prior use of alcohol or drugs. The study does not provide a separate estimate of the risk of SIDS while sharing a bed with a parent in the absence of these and other risk factors. Although previous campaigns have had much success, advising parents to avoid risky co-sleeping environments might reduce the risk of cot death even further.
The study has some unavoidable limitations that must be considered:
- Not all of the parents whose babies had died of cot death participated in this study, so there would be a number of families and circumstances not included that may have provided different information and so altered the results.
- As cot death is a rare occurrence, the numbers in the case and control groups are relatively small. As such, it cannot give reliable proportions and risk figures as would be possible from a larger study population. The estimates of risk are imprecise for this reason.
- From the questions asked, it is not possible to gain complete information about all of the circumstances surrounding cot death, for example co-sleeping on a sofa. It is not clear whether this was just a one-off occasion at the time the baby died, whether this was a regular daytime habit of the baby and parent, or if this was the regular night-time sleeping arrangement.
- The causes of cot death are not completely understood, so there may be other risk factors not included in this study that increase or reduce risk. The researchers used a statistical technique where the risk associated with each factor was adjusted for the risk associated with other factors, but they may not have accounted for some of the unknown associations.
It is likely that this research will go towards further information, campaigns and advice for parents on how to provide the safest and healthiest environment for their baby. Visit Health A-Z: cot death for the latest advice.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
BBC News, 14 October 2009
The Daily Telegraph, 14 October 2009
The Independent, 14 October 2009
Daily Express, 14 October 2009
The Times, 14 October 2009
Links to the science
BMJ 2009; 339: b3666