In the first of a two-part article, Ms Jeanine Young and Professor Peter Fleming assess the risk factors which lead to sudden infant death

Jeanine Young is Research Nurse/Associate; Peter J Fleming is Professor for Infant Health and Developmental Physiology, Sebastian Diamond Mother & Baby Sleep Physiology Laboratory, St Michael's Hospital, Bristol


Sudden infant death syndrome (SIDS), or cot death, is 'the sudden death of an infant which is unexplained after review of the clinical history, examination of the circumstances of death, and post mortem examination'¹. There is consensus in the literature that a number of different factors, rather than a single cause, are involved in cot death². Several factors acting together at a vulnerable stage of development in a predisposed infant may, in some cases, overwhelm a baby's ability to cope.

Prevalence

Recent research has identified risk factors for SIDS, some of which are potentially modifiable, and others which are not. The identification of modifiable risk factors is important in disease prevention and assists in the quest to understand the pathogenesis of SIDS. In Britain, SIDS rates have reduced dramatically since the 'Back to Sleep' campaign in 1991³ in which parents were advised to place their babies on their backs to sleep. The rate of SIDS (expressed per 1000 live births) was 1.7 in 1990 and fell to 0.68 in 1993 and 1994, and 0.6 in 19954. Although the rate has remained relatively unchanged (0.5-0.7/1000 live births since 1992⁴) SIDS remains the largest single category of deaths in infancy⁵.

In 1996, the number of cot deaths rose for the first time in eight years; an increase of six per cent to 0.7/1000 live births⁴. The rise is unexplained, however a major possibility is that the 'reduce the risk' messages are not reaching some parents and carers, or there may be a false belief that cot death is no longer a problem⁴. Continued emphasis of the campaign message and surveillance are required to ensure that the progress is sustained⁴.

Prevention

Results from the first two years^8,9 of a three-year case-control study of stillbirths and sudden unexpected deaths in infancy6 found that current advice appears to be correct but is either not being received or not being implemented by a proportion of the population at risk. The report stated that a further reduction in the incidence of SIDS would be achieved if all parents and childcarers adhered to the current recommendations (see Table 1). Previously recognised factors associated with SIDS remain relevant, with clear differences between cases and controls. Refinements and extensions to current national recommendations were proposed, and there are some factors which require further research⁴.

GPs can play a major preventive role in SIDS by providing parents and other infant caretakers with information regarding the possible causes of SIDS and advising against exposure to any known high-risk conditions or infant care practices. The summary of the epidemiology of SIDS (see below) and of current recommendations presented are provided as a resource for GPs to use in identifying vulnerable families in their care and planning interventions that will help reduce the risk of infants dying in this way.

Bed-time risk factors

Sleeping position. The risk of cot death is nine times higher if babies sleep prone rather than supine². An important new observation is that the side-sleeping position carried a significantly increased risk when compared with the supine position, regardless of whether the lower arm was extended forward or not^6,7. Much of the increased risk of the side-sleeping position is related to the risk of the baby placed to sleep on the side and rolling to the prone position^2,6.

There is no evidence that sleeping supine increases the risk of aspiration; in fact the risk of aspiration, as well as the incidence of respiratory and ear infections, is higher in infants sleeping prone^2,8. Infants with abnormalities of the upper airway such as Pierre Robin syndrome, are at risk of lethal upper airway obstruction if placed supine, and therefore need to be nursed prone or in the side position for sleep². Gastro-oesophageal reflux is known to be exacerbated by the supine position. However unless the reflux is severe, symptomatic and causing apparent life-threatening events which are not responding to medical management, the supine sleeping position is still recommended2. For some infants with severe reflux the left lateral position may help reduce symptoms⁹. l

Sleeping location. Many parents ask whether it is safe to take their baby to bed with them. Research in this area has been conflicting. Some studies identify bedsharing as a risk factor for SIDS10, while others acknowledge the beneficial effects of close contact between babies and their caregivers11 and the low incidence of SIDS in cultures, particularly Asian communities, in which mothers traditionally sleep very close to their babies, often in the same bed¹².

Recent research has shown that bedsharing for the whole night is associated with an increased risk only if the mother is a smoker or has consumed alcohol or other drugs of abuse^6,7. The vast majority of bedsharing mothers whose baby died of SIDS were smokers (86.2 per cent) and the associated risk to infants of these mothers was extremely high (OR 21.13; 95 per cent CI 9.36 to 48.55), whilst being non-significant amongst infants of non-smoking mothers⁶.

In New Zealand¹³ and the United Kingdom (Fleming PJ and Blair PS, personal communication), sharing a room with a parent was shown to have a protective effect against SIDS. Recent studies have emphasised the potential hazard of adults sleeping on a sofa or couch with a baby. Advice such as 'all babies' should be returned to their cot after breastfeeding (Table 1)³ errs on the side of caution, and further study is required before such a statement could or could not be made definitive. Current advice to parents who wish to bedshare should include statements listed in Table 2.

There is no published evidence of any increased risk to a baby from sharing a bed with a firm mattress with parents who do not smoke and have not consumed alcohol or other drugs, provided the bedding is arranged so that it cannnot slip over the baby's head, and the baby is not sleeping on a pillow, or under an adult duvet.

Head covering. Almost 20 per cent of SIDS babies were found with their heads completely covered by bedclothes which was associated with a 20-fold increased risk¹⁴. Loose bedding, particularly duvets and quilts which can easily slip over a baby's head, carry a very high odds ratio (OR 21.58; 95 per cent CI 6.21 to 74.99)², and are consequently no longer recommended for use for infants under one year³.

Parents should be advised to place the baby in a 'feet to foot' position, in which the baby's feet are at the foot of the cot, and bedding is tucked securely in at the bottom of the cot, to reduce the risk of bedding slipping over the baby's head⁸. Pillows should not be used.

Mattresses. Much concern to parents and health care professionals has been caused by the media controversy in 1994 which linked cot death with chemical poisoning from PVC-covered mattresses. However, this theory has since been rejected because no evidence has been found to substantiate the claims¹⁹. The Limerick Committee, an expert working group set up by the Department of Health in 1995 to investigate the mattress theory and other SIDS-related issues, reported its findings in Ma, 1998¹⁶. After an exhaustive investigation of the toxic gas hypothesis, methodically examining every aspect of the claim both by reviewing existing research, as well as by commissioning new research, the Expert Group concluded that there was no evidence to support the claim that fire retardants in PVC cot mattresses cause cot deaths^15,16.

GP advice to parents should include that any mattress is suitable as long as it is in good condition, flat, has a firm surface and is kept clean and dry and is well aired. Research does not support suggestions that any particular type of mattress reduces the risk of cot death. The 'ventilated' portion present in some cot mattresses has not been shown to be of value in preventing SIDS, and may make the mattress more difficult to keep clean.

The baby should be in a 'feet to foot' position, regardless of the position of the 'ventilated' section. Bedding should be tucked in firmly so that it cannot ride up over the baby's head. There is no evidence that waterproof mattress covers are unsafe; they must be firmly fixed to the mattress and kept clean. If a second hand mattress has been well stored, is firm, flat and clean, and is not damp or torn in any way, then it can be used again. If there is any doubt about a mattress, then advise parents to buy a new one; preferably one that can be cleaned easily. Pillows should not be used¹⁷.

Thermal insulation. High room temperature, overwrapping, or both, is associated with an increased risk of cot death. However, in recent studies heavy wrapping, although still an important factor, has less effect in a population of infants in which few sleep prone. Infection, sleeping position and bedding arrangements may interact with thermal insulation to increase the risk^6,14. Parents are advised to use the guidelines for bedding and clothing in the Department of Health and FSID's leaflet Reduce the Risk of Cot Death Ñthe Easy Guide¹.

Resuscitation

Lastly, the importance of cardiopulmonary resuscitation (CPR) education for all new parents cannot be overemphasised. This skill is vital not just for infants in potential SIDS situations, but also for foreign-body aspiration, drowning, electrocution, and trauma. Parents who have been taught CPR as basic child care report increased confidence and an associated reduction in anxiety with their ability to handle any situation that may arise¹⁹.

Conclusion

It is likely that a further reduction in the rate of SIDS would be achieved if all parents or child carers were able to adhere to the key health messages which relate mainly to baby night-time sleeping arrangements³, although there will always be rare and distressing situations. The Confidential Enquiry reported that the standard of care from health care professionals may have been a contributing factor in up to 32 per cent of sudden infant deathsÑparticularly those in which infection may have played an important part. The major problem identified was poor communication with vulnerable families³. The Department of Health and the FSID responded by publishing a new leaflet on Reducing the Risk¹⁸ outlining the key health messages.

GPs commonly have a close relationship with parents and are very influential. They have an important role to play in the reduction of sudden unexpected deaths in infancy and GPs can do this by ensuring that all parents of babies in their care have the opportunity to receive advice and information about ways in which they can reduce the risk of SIDS. In the part of this article[Go to part 2], the authors will look at risk factors other than those specific to night-time.

References
1 Rognum TO, Willinger M. The story of the Stavenger definition. In: Rognum TO. (Ed). Sudden infant death syndrome : new trends in the nineties. Scandinavian University Press. Oslo 1995: 21-25
2 Fleming PJ and Blair PS. The Role of Sleeping Position in the Aetiology of the Sudden Infant Death Syndrome. In: Hansen TN, McIntosh N (Eds). Current Topics in Neonatology Number 2. W.B. Saunders. London 1997: 21-38
3 Department of Health. Confidential Enquiry into Stillbirths and Deaths in infancy, 3rd Annual Report : Executive Summary and Recommendations. Concentrating on the first two years of combined studies on Sudden Unexpected Deaths in Infancy. HMSO. London 1996
4 Foundation for the Study of Infant Deaths. Cot deaths rise by 6 per cent. FSID News: Newsletter for the Foundation for the Study of Infant Deaths. Spring 1998; Number 57:3
5 Wigfield R, Fleming PJ. The prevalence of risk factors for SIDS: impact of an intervention campaign: In: Rognum TO. (Ed).Sudden infant death syndrome: new trends in the nineties. Scandinavian University Press. Oslo 1995: 124-8
6 Fleming PJ, Blair PS, Bacon C et al. Environment of infants during sleep and risk for SIDS : results of 1993-95 case-control study for confidential inquiry into stillbirths and deaths in infancy. Br Med J 1996; 313 : 191-95
7 Mitchell EA, Tuohy PG, Brunt JM et al. Risk Factors for Sudden Infant Death Syndrome Following the Prevention Campagin in New Zealand. Pediatrics 1997; 100(5): 835-40
8 Hunt L, Golding J, Fleming PJ. and the ALSPAC study team. Does the supine sleeping position have any adverse effects on the child ?: 1) Health in the first six months. Pediatrics 1997; 100: 1: ell (electronic pages) (http://www.pediatrics.org/cgi/content/full/100/1/ell)
9 Tobin JM, McCloud P, Cameron DJS. Posture and gastro-oesophageal reflux: a case for left lateral positioning. Archives of Disease in Childhood 1997; 76: 254-258
10 Mitchell EA, Taylor BJ, Ford RPK et al. Four modifiable and other major risk factors for cot death: the New Zealand study. J Paediatric Child Health 1992; 28(suppl. 1):S3-8
11 McKenna J, Mosko S, Richard C, Drummond S, Hunt L, Cetal MB, Arpaia J. Experimental studies of infant-parent co-sleeping: mutual physiological and behavioural influences and their relevance to SIDS (sudden infant death syndrome). Early Human Development 1994; 38: 187-201
12 Nelson EAS, Chan PH. Child care practices and cot death in Hong Kong. New Zealand Medical Journal 1996; 109(1020): 144-146
13 Scragg RKR, Mitchell EA, Stewart AW et al. Infant room-sharing and prone sleep position in sudden infant death syndrome. Lancet 1996; 347: 7-12
14 Foundation for the Study of Infant Deaths. Factfile 1 : Cot Death - Facts, Figures and Definitions. Foundation for the Study of Infant Deaths. London 1997
15 Blair PS, Fleming PJ, Bensley D, Smith I, Bacon C, Taylor E. Plastic Mattresses and sudden infant death syndrome. Lancet 1995; 345(8951): 720
16 Blair PS, Fleming PJ, Cook M et al. Supplementary studies to establish whether antimony or other chemicals added to cot mattress covers are of significance in the aetiology of Sudden Infant Death. Appendix 3. In: Expert Group chaired by Lady Limerick. Expert group to investigate cot death theories: toxic gas hypothesis. Final report, May 1998. Department of Health. London 1998: 311-338
17 Foundation for the Study of Infant Death. FSID statement : Cot mattresses. FSID. London, 8th May, 1997: 1-2
18 Department of Health Reduce the Risk : An Easy Guide. Department of Health & FSID. London, 1996
19 Donaher-Wagner BM, Braun DH. Infant cardiopulmonary resuscitation for expectant and new parents. MCN : Am J Maternal-Child Nursing 1992; 17 (1): 27-9

More information
For copies of the free booklet: Reduce the Risk of Cot Death : An Easy Guide, write to: Department of Health, PO Box 410, Whetherby, LS23 7LN.
For more information on cot death send an s.a.e. to: The Foundation for the Study of Infant Deaths (FSID), 14 Halkin St, London SW1X 7DP.
Tel: 0171 235 0965 Helpline: 0171 235 1721

In the second part or their article about SIDS, Jeanine Young and Professor Peter Fleming look at risk factors other than those specific to night time

Research investigating the epidemiology of sudden infant death syndrome (SIDS) has revealed certain features of the baby, the family, and the circumstances which are associated with an increased risk of SIDS. Identifying risk factors which have shown to be associated with SIDS provides parents with a useful guide of situations to avoid. Many of these risk factors are inherent during the night (see last monthÕs issue of Family Medicine), but there are many other important contributing factors to consider

Infant factors. Some features of SIDS remain essentially unchanged. Babies of low birth weight, short gestation (preterm), multiple births, and higher birth order are at greater risk, and there remains a preponderance of boys1,2. There is a characteristic age distribution for SIDS which differs from most other causes of infant death: the risk of SIDS peaks between two and three months of age, decreases as the baby gets older and is very low beyond nine months².

Parental factors. SIDS is more common in babies of younger mothers, and particularly those without a supportive partner. A higher maternal parity (particularly for mothers under the age of 25) and where there was a shorter interval (less than six months) between pregnancies also increases the risk².

Socio-economic factors. The previously recognised association between SIDS and socio-economic deprivation now seems more marked. The cot death rate increases with decreasing occupational status and lower educational achievement. Approximately 80 per cent of cot deaths occur in lower social groups. There was a striking excess of SIDS families in which neither partner was employed (45 per cent) and in 13.3 per cent neither partner had ever been employed since leaving school¹. A recent move of house, before, during or after the pregnancy, has also been identified as a factor in families at a greater risk of SIDS.

Smoking. Maternal smoking during pregnancy increases the risk of SIDS and there is a biological gradient: smoking from one to nine cigarettes per day in pregnancy increased the risk more than four times; 10-19 cigarettes per day increased the risk more than five times, and more than 20 cigarettes per day was associated with an eight-fold increase^2,3. Paternal smoking had an additional independent effect (OR 2.50; 95 per cent CI 1.48 to 4.22)3.

Exposure of babies to tobacco smoke from other members of the household, before and after birth, also increases the risk of death: the greater the exposure the higher the risk (see Figure 1). This figure shows that for every hour of the day that babies habitually spent in a room in which people smoked, the risk of SIDS increased by almost 100 per cent. The risk to babies who spent more than eight hours a day in such a room was more than eight times that to babies who were not exposed to tobacco smoke.

Evidence from at least 24 cohort and case-control studies worldwide, which have investigated the relationship between maternal smoking and SIDS, strongly suggests that smoking is causally related to SIDS⁴. The population attributable risk of 61.2 per cent found in the CESDI SUDI investigation implies that the number of deaths from SIDS in the UK could be reduced by almost two thirds if parents did not smoke³.

Illness

Having features of illness requiring professional advice is associated with increased risk, although three quarters of infants who died of SIDS had only minor symptoms or signs, or none at all, prior to their death¹.

Interventions such as parental education in early illness detection may also have the potential to help reduce the incidence of SIDS. Thornton and colleagues5 developed the ÔBaby Check Score CardÕ which consists of a graded checklist of signs and symptoms creating a score on which action to seek medical help or treatment can be based. The potential value of this scoring system has been supported by a study which showed that a significant number of infants who died of SIDS would have been identified as potentially seriously ill by using the Baby Check Score Card⁶. A high score or a history of an apparent life threatening event, are acute factors which may signify transient increased risk and alert the family and the GP, or other health care professionals, to the need for close observation or possible treatment.

Breastfeeding

Breastfeeding was not included in the 'Reduce the Risk' campaign because research on the absence of breastfeeding and cot death is inconsistent7,8. In the CESDI SUDI study, no independent protective effect was identified from breastfeeding when other significant factors were controlled9. Similar results were found after the intervention campaign in New Zealand¹⁰. A large study, before the 'Back to Sleep' campaign in Avon and North Somerset, found bottle feeding was not a significant independent risk factor for SIDS¹¹. However, breastfeeding has many benefits and should be encouraged as good practice for many other reasons; for example to reduce the risk of infections and promote recovery from infection2.

Seasonality

A characteristic feature of SIDS before 1991 was a marked peak of deaths in winter, with about 67 per cent occurring in the six winter months⁸. Since the 'Back to Sleep' campaign, the winter peak has progressively become less marked, and now seems to have disappeared, although the reason for this is not known.

Immunisation

The possibility of the DTP (diptheria-tetanus-pertussis) vaccination being linked to SIDS has been raised periodically over the last 20 years. This is due to a small number of SIDS deaths which occurred within a few days of immunisation, and the peak age distribution for SIDS coinciding with the timing for infantsÕ immunisations. The evidence from many large studies world-wide shows overwhelmingly that immunisation is associated with a decreased, not an increased, risk of SIDS. All parents are strongly advised to follow national recommendations and have their babies immunised at the appropriate times¹³. Dummies Studies in the UK⁸ and New Zealand¹³ have shown that dummy use may be associated with a decreased risk of SIDS. However, in the CESDI study the possibility was raised that the risk may be highest for babies who usually had a dummy but failed to do so on a particular night. The reported adverse effects of dummy use on breastfeeding, together with the CESDI finding, suggest caution in recommending dummy use as a routine at present⁹.

Caffeine

The media has recently drawn attention to findings in the New Zealand Cot Death Study which indicate that heavy caffeine intake (defined as 400 mg or more; equivalent to four or more cups of coffee per day) during pregnancy may increase the risk for SIDS¹⁴. Data used for this research was collected in 1987-1990 before the dramatic decline in cot death of the early 1990s, and it is not known whether a similar relationship would be found for cot death occurring now¹⁵. This research should be confirmed by further studies before a reduction in caffeine intake is recommended in pregnancy.

Flying

Even more recently, attention has been drawn to the possibility that flying may be hazardous for babies as they may breathe lower than usual levels of oxygen in the cabin atmosphere. Researchers¹⁶ demonstrated that some babies react more dramatically than others to a drop in oxygen. This study did not demonstrate a greater cot death risk to babies on an aeroplane than those on the ground. However, children do find themselves in situations where oxygen levels drop, and so these interesting findings need to be further investigated. Parents should be urged not to panic, as epidemiological findings indicate that, whatever the effect of relative hypoxia on breathing patterns, flying appears to be safe for healthy children in the first year of life^17,18.

Conclusion

Although the key health messages about reducing the risk of SIDS relate mainly to night-time sleeping arrangements, other important factors have been identified. Some of these factors are potentially modifiable and need to be relayed to parents, for example parental smoking. Other factors which are not as amenable to change, such as socioeconomic status, can be used by health professionals to identify and target interventions for families who may be at an increased risk of SIDS. All health professionals involved in family medicine have a role to play in reducing the risk of sudden unexpected deaths in infancy. They can do this by ensuring all parents of babies in their care have the opportunity to receive advice and information about ways to reduce the risk of SIDS

References
1 Department of Health. Confidential Enquiry into Stillbirths and Deaths in infancy, 3rd Annual Report: Executive Summary and Recommendations. Concentrating on the first two years of combined studies on Sudden Unexpected Deaths in Infancy. HMSO. London 1996
2 Foundation for the Study of Infant Deaths. Factfile 1: Cot death - facts, figures and definitions. Foundation for the Study of Infant Deaths. London 1997
3 Blair PS, Fleming PJ, Bensley D et al. Smoking and the sudden infant death syndrome: results from 1993-95 case-control study for confidential inquiry into stillbirths and deaths in infancy. Br Med J 1996; 313: 195-8
4 Mitchell EA. Smoking: The next major and modifiable risk factor. In: Rognum TO. (Ed). Sudden infant death syndrome: new trends in the nineties. Scandinavian University Press. Oslo 1995: 114-18
5 Thornton AJ, Morley CJ, Green SJ, Cole TG, Walker KA, Bonnette JM. Field trials of the Baby Check Score Card: Mothers scoring their babies at home. Archives of Disabled Children 1991; 66: 106-10
6 Cole TG, Gilbert RF, Fleming PJ et al. Baby check and the Avon Infant Mortality study. Archives of Diseases in Childhood 1991; 66: 1077-8
7 Golding J. Breastfeeding and sudden infant death syndrome. In: Department of Health. Report of the Chief Medical Officer's Expert Working Group: The sleeping position of infants and cot death. HMSO. London 1993
8 Silvester J. Cot death update: The current state of knowledge regarding the risk factors for cot death. J Neonatal Nursing 1995; 1(4): 17-19
9 Fleming PJ, Blair PS, Bacon C et al. Environment of infants during sleep and risk for SIDS: results of 1993-95 case-control study for confidential inquiry into stillbirths and deaths in infancy. Br Med J 1996; 313: 191-5
10 Mitchell EA, Tuohy PG, Brunt JM et al. Risk Factors for sudden infant death syndrome following the prevention campaign in New Zealand. Pediatrics 1997; 100(5): 835-40
11 Gilbert R, Wigfield R, Fleming PJ, Berry PJ, Rudd PT. Bottle feeding and the sudden infant death syndrome. Br Med J 1995; 310: 88-90
12 Foundation for the Study of Infant Deaths. Immunisation and cot death. FSID News: Newsletter for the Foundation for the Study of Infant Deaths. Autumn 1997; Number 56: 5
13 Mitchell EA, Taylor BJ, Ford RPK, Stewart AW, Becroft DMO, Thompson JMD, et al. Dummies and the sudden infant death syndrome. Archives of Diseases in Childhood 1993; 68: 501-4
14 Ford RPK, Schluter PJ, Mitchell EA et al. Heavy caffeine intake in pregnancy and sudden infant death syndrome. Archives of Diseases in Childhood 1998; 78: 9-13
15 Ford R et al. Foundation for the Study of Infant Deaths. Heavy caffeine intake in pregnancy and SIDS 1998: 1
16 Parkins KJ, Poets CF, OÕBrien LM, Stebbens VA, Southall DP. Effect of exposure to 15 per cent oxygen on breathing patterns and oxygen saturation in infants: interventional study. Br Med J 1998; 316 (7135): 887-91
17 Foundation for the Study of Infant Death. FSID response to article. Br Med J 1998; 316 (7135): 887-91. 'Effect of exposure to 15 per cent oxygen on breathing patterns and oxygen saturation in infants', Parkins KJ. et al. FSID. London, 20th March 1998: 1
18 Milner AD. Effects of 15 per cent oxygen on breathing patterns and oxygenation in infants: infants are probably safe in aircraft. Br Med J 1998; 316 (7135): 873-4