Sleeping position and sudden infant death syndrome (SIDS): effect of an intervention programme to avoid prone sleeping

The proportion of prone sleeping among sudden infant death syndrome (SIDS) victims and infants in general, and the rate of SIDS were prospectively studied in the county of Hordaland, Norway, three years before (1987–89) and three years after (1990–92) a campaign to discourage prone sleeping. Before the campaign, 64% of random reference infants were put prone versus 8% after (p < 0.0001). Concurrently, the rate of SIDS decreased from 3.5 to 1.6 per 1000 live births (63 infants before and 30 after the campaign, p = 0.0002). Prone sleeping was not considered a statistically significant risk factor for SIDS before (OR 2.0,95% CI 0.8–4.5), but was highly significant (OR 11.3,95% CI 3.6–36.5) after the campaign. Prone sleeping is an important risk factor for SIDS, but the association may be missed in epidemiological studies if prone is the predominant sleeping position. Behaviour with regard to sleeping position may be changed rapidly by means of a simple campaign.     

Further evidence supporting a causal relationship between prone sleeping position and SIDS

Abstract A 3 year case-control study identifying the risk factors for SIDS was undertaken. Preliminary analysis of the data from the first year suggested that SIDS mortality could fall by 50% if the prevalence of the prone sleeping position changed from 40 to 0%. During the 3 year study the prevalence of the prone sleeping position among infants has fallen from 43% in the first year to 20% in the third year. SIDS mortality has fallen to 3.1/1000 live births, which is very close to that predicted. When considered with other available evidence this strongly supports a causal relationship between the prone sleeping position and SIDS.     

An overview of retrospective case-control studies investigating the relationship between prone sleeping position and SIDS

A critical overview of 19 case-control studies that have investigated the relationship between prone sleeping position and sudden infant death syndrome (SIDS) is presented. Issues relating to the non-comparability of the studies are described in terms of: (i) case definition; (ii) selection of controls; (iii) quality of the sleeping position data; (iv) recall bias; and (v) adjustment for confounding factors. All studies showed a positive association (2 out of the 19 studies were not significant) between prone sleeping position and SIDS. Meta-analysis techniques applied to six of these studies, based on 'usual' sleeping position in cases and population representative controls, has confirmed an overall higher risk of SIDS in infants who usually sleep prone. The most common odds ratio for an association between prone sleeping position and SIDS was 2.72 (95% confidence interval 2.27-3.26). The extent to which the methodological problems of retrospective case-control studies interfere with our interpretations of this association are discussed.     

An 8 year study of risk factors for SIDS: bed-sharing versus non-bed-sharing

Background

It is unclear if it is safe for babies to bed share with adults. In Ireland 49% of sudden infant death syndrome (SIDS) cases occur when the infant is bed‐sharing with an adult.

Objective

To evaluate the effect of bed‐sharing during the last sleep period on risk factors for SIDS in Irish infants.

Design

An 8 year (1994–2001) population based case control study of 287 SIDS cases and 831 controls matched for date, place of birth, and sleep period. Odds ratios and 95% confidence intervals were calculated by conditional logistic regression.

Results

The risk associated with bed‐sharing was three times greater for infants with low birth weight for gestation (UOR 16.28 v 4.90) and increased fourfold if the combined tog value of clothing and bedding was ⩾10 (UOR 9.68 v 2.34). The unadjusted odds ratio for bed‐sharing was 13.87 (95% CI 9.58 to 20.09) for infants whose mothers smoked and 2.09 (95% CI 0.98 to 4.39) for non‐smokers. Age of death for bed‐sharing and sofa‐sharing infants (12.8 and 8.3 weeks, respectively) was less than for infants not sharing a sleep surface (21.0 weeks, p<0.001) and fewer bed‐sharing cases were found prone (5% v 32%; p = 0.001).

Conclusion

Risk factors for SIDS vary according to the infant''s sleeping environment. The increased risk associated with maternal smoking, high tog value of clothing and bedding, and low z scores of weight for gestation at birth is augmented further by bed‐sharing. These factors should be taken into account when considering sleeping arrangements for young infants.     

Changes in parental risk behaviour after an information campaign against sudden infant death syndrome (SIDS) in Norway

AIM: To assess parental risk behaviour before and after a sudden infant death syndrome (SIDS) information campaign with special emphasis on associations with maternal age, education, marital status and birth order. METHODS: Data from questionnaires sent to all mothers who gave birth in Norway during a period before the campaign were compared with corresponding data obtained after the campaign. RESULTS: Prevalence of non-supine sleeping position decreased from 33.7% to 13.6% while changes in smoking, non-breastfeeding and co-sleeping were disappointing. Risk factors were particularly prevalent in young mothers, but also in mothers with a minimum period of education, non-cohabitation and at birth order 2+. CONCLUSIONS: Non-supine sleeping decreased to a level that has never been reported before. In future campaigns, subgroup-specific measures may be needed.     

Prone sleeping position and SIDS: Evidence from recent case-control and cohort studies in Tasmania

The most recent data from the cohort and case-control studies of SIDS and prone position recently reported from Tasmania are reviewed. The cohort analysis was based on 4103 infants born between 1 January 1988 and 1 December 1990 assessed as being at high risk at birth, of whom 29 later died of SIDS. A matched analysis which controlled for infant birthweight and maternal age indicated that prone sleeping position was associated with an increased risk of SIDS (OR 3.92, 95% Cl [1.37-11.24]). The case-control study was based on all (n = 55) Tasmanian SIDS death from October 1989 to April 1991 and matched live controls. The unadjusted odds ratio for prone position and SIDS was 5.04 (95% Cl [2.29-11.11]). The population attributable risk percentage, based on the high risk cohort data, was 0.38 (95% Cl [0.35-0.41]), suggesting that a significant reduction in SIDS incidence might occur if the prevalence of the prone sleeping position in the infant population were reduced. Other factors which may be important for the development of any public health interventions to reduce SIDS based on these findings are discussed.     

SIDS outdoors and seasonality in Sweden 1975–1987

In order to link the reported increasing incidence of SIDS in Sweden to environmental or other risk factors, we compared birth records and circumstances of deaths in infants who died in 1975–1977 with those who died a decade later, 1985–1987. The number of live births differed by only 6850 in these two periods. Data were acquired from autopsy records of the deceased infants and matched with their respective birth certificates which were obtained from the National Board of Health and Welfare. The reported postperinatal incidence of SIDS increased from 0.51 per 1000 in 1975–1977 to 0.93 per 1000 in 1985–1987. No significant differences in boy/girl ratio, birth weight, gestational age or age at death were found in the two periods. While the number of infants who died at night indoors in their own bed remained almost unchanged, the number of infants who died outdoors in baby carriages during the cold season increased almost four-fold. The observed increase in incidence could, to a large extent, be related to the increase in outdoor deaths. We speculate that increased incidence of smoking among young women as well as other changes in lifestyle may have been contributing factors.     

SIDS risk factors and factors associated with prone sleeping in Sweden.

OBJECTIVE: To compare the current prevalence of risk factors for sudden infant death syndrome (SIDS) in Sweden with a decade earlier, and assess factors associated with prone sleeping. METHODS: The results of a cohort study (Infants of Western Sweden) and a population based case-control study (Nordic Epidemiological SIDS Study) were examined. Subjects were 5600 healthy 6 month old infants born in 2003 in the Western Sweden region and 430 healthy Swedish infants born between 1991 and 1995. RESULTS: Prone sleeping decreased from 31.8% to 5.6% and supine sleeping increased from 35.3% to 47.3%. Side or side/supine sleeping increased from 25.2% to 43.8%. Maternal smoking during pregnancy decreased from 23.5% to 9.5%. The risk for prone sleeping increased if the mother was unemployed (OR 2.4, 95% CI 1.5 to 4.0), if she was a heavy smoker in the third trimester (OR 44.1, 95% CI 1.6 to 1199.6), and if the child was irritable (OR 2.5, 95% CI 1.3 to 5.1), shared a bedroom with siblings (OR 2.6, 95% CI 1.0 to 6.6), or never used a dummy (OR 3.2, 95% CI 1.9 to 5.4). CONCLUSIONS: Parents have complied with advice to prevent SIDS given at infant welfare centres for the last 10 years. A change in the preferred sleeping position from side variants to exclusively supine, and reducing the number of pregnant women smoking may be beneficial. Use of a prone sleeping position was associated with maternal employment status, maternal smoking, temperament of the child, dummy use, and sharing a bedroom with siblings.     

Nicotine and cotinine levels in pericardial fluid in victims of SIDS

Milerad J, Rajs J, Gidlund E. Nicotine and cotinine levels in pericardial fluid in victims of SIDS. Acta Paediatr 1994;83:59–62. Stockholm. ISSN 0803–5253
We have analyzed the levels of nicotine and cotinine in pericardial fluid in 24 consecutively autopsied cases of sudden unexpected death in infants aged one to six months. Our aim was to determine to what extent victims of sudden infant death may have been exposed to passive smoking near the time of death. Sixteen of the decreased infants were classified as SIDS at autopsy. Other contributing causes of death, predominantly infections, were found in eight cases. Eight infants (30%) had cotinine levels less than 2 ng, indicating that no significant exposure to nicotine had occurred near the time of death. Of the remaining 70%, five had been moderately exposed, seven markedly exposed and four heavily exposed (cotinine levels 2–10 ng, 10–50 ng and more than 50 ng, respectively). Since only 18% of Swedish women smoke after childbearing we conclude that nicotine exposure in infants who died suddenly was much higher than one would otherwise expect. It is hypothesized that high concentrations of nicotine and nicotine metabolites around the heart may affect cardiac function and thus play a role in the mechanisms causing SIDS or other categories of sudden unexpected death.     

An analysis of trends in the incidence of sudden infant death in The Netherlands 1969–89

There is considerable interest in the relationship between sleeping position and the occurrence of sudden infant death syndrome (SIDS). As changes have been reported in The Netherlands in the position infants have been placed to sleep, the national Dutch sudden infant death rates were analyzed over the time that such changes have taken place. The overall post-perinatal death rate (1 week less than 1 year) was around 4-4.5 per 1000 live births from 1969 until 1985. From 1985 until 1989 the rate fell from 4.1 to 2.9 per 1000 live births. During the same period the cot death/SIDS rate rose from 0.44 per 1000 in 1969 to between 1.08 and 1.31 per 1000 in 1977-87, and subsequently fell to 0.7 per 1000 in 1989. These trends coincided with changes in prone sleeping position demonstrated in national surveys. The problems of interpreting such national data, with only 50-60% of infant deaths being autopsied and with the possibilities of misclassification over time, are fully discussed. The data are supportive of the relationship between prone sleeping position and cot death.     

Interactions between maternal smoking and other prenatal risk factors for sudden infant death syndrome (SIDS)

Abstract In numerous investigations, maternal smoking increases the risk of sudden infant death syndrome (SIDS). In the present study we investigated whether prenatal risk factors for SIDS modify the effect of maternal smoking on SIDS mortality. We analysed data from a population-based cohort study (222 cases, 260,604 infants at risk) within the Westphalian Perinatal Inquiry in Germany between 1990 and 1994. In the stratified analysis, smoking was classified into non-smoking, moderate (1–10 cigarettes/d) and heavy smoking (> 10 cigarettes/d). Multiplicative interactions between smoking and other prenatal risk factors were assessed in a logistic regression model. The relative risk (RR) for maternal smoking was 2.4 (95% confidence interval 1.7-5.4) for moderate and 7.2 (5.3, 9.7) for heavy smokers. Previous established risk factors for SIDS, such as preterm birth, low birthweight, and number of prenatal visits did not increase the risk of SIDS among non-smokers, but became important risk factors among smokers. In preterm infants (< 37 weeks) of heavy smokers, the RR was 19.6 (10.4, 36.8) compared to term infants of non-smokers. Low birthweight infants (< 2500 g) of heavy smokers had a RR of 16.3 (8.4, 31.2) compared to normal weighted infants of non-smokers. Adjustment for occupational status did not change the crude estimates. The RR of < 6 prenatal visits in the heavy smoking subgroup was 14.8 (7.2, 29.6) compared to > 9 prenatal visits in the nonsmoking strata. Heavy smoking potentiates other prenatal risk factors for SIDS suggesting an increased susceptibility towards the adverse effects of tobacco smoke in utero. In infants born to non-smoking mothers, prenatal risk factors are absent and postnatal factors may be of major importance.     

Mothers' knowledge of the risk factors and anxiety about SIDS

Objective : To assess the impact on mothers' knowledge and anxiety of the 1991-92 health promotion campaign on Sudden Infant Death Syndrome (SIDS) risk factors.
Methodology : A telephone survey of a population based sample of 339 mothers in Victoria, Australia, conducted 1992-94.
Results : Recall by mothers of the risk factors for SIDS was as follows: not breast-feeding. 15%; smoking, 46%; overheating, 48%; and prone sleeping, 84%. Recall rate increased as the campaign progressed. Receiving the campaign pamphlet was associated with an increased recall of all risk factors. Discussion of the pamphlet with a health professional was rare (9%). One-third of all mothers reported being very worried about cot death when caring for their babies. Self-reported worry was significantly more common among mothers whose babies were born at the time of the campaign introduction.
Conclusions : The campaign pamphlets were effective in increasing knowledge of the risk factors. The limited discussion with health professionals suggests that future campaigns need increased professional involvement to address problems, including anxiety among new mothers.     

What else do SIDS risk prediction scores predict?

Various aspects of the medical and social history of 12 743 children examined at the age of 5 years were related to two risk scores for the sudden infant death syndrome (SIDS) computed from data collected in the neonatal period. Children at high risk of SIDS were also at high risk of pneumonia, non-accidental injury and repeated or prolonged hospital admissions. There were stronger associations, however, with factors indicating social disruption and environmental disadvantage.     

Carbon dioxide concentrations in the environment of sleeping infants

Abstract In 22 infants continuous measurements were made of the concentration of carbon dioxide (CO₂) in inspired air during sleep. Evidence was found of CO₂ enrichment of inspired air in certain environmental conditions. The levels achieved were not sufficiently high to acutely endanger an infant. Carbon dioxide concentrations as high as 2-3% were observed in the prone position when the infant's head was under a blanket and when the lower face was obscured by bedding. Sleeping prone on a sheepskin also resulted in an increased concentration of CO₂ but to a lesser extent than being under a blanket. In awake infants the presence of a pacifier also promoted an excess of CO₂ in the inspired air, both in the prone and supine positions. The physiological and clinical implications of these findings, in relation to the Sudden Infant Death Syndrome (SIDS), are unknown and warrant investigation.     

Sudden infant death syndrome (SIDS) in South Australia 1968-97. Part 2: the epidemiology of non-prone and non-covered SIDS infants

OBJECTIVE: To identify the risk factors for infants who die suddenly and unexpectedly, but whose deaths are not related to prone position, or having the head covered. METHODOLOGY: A case-control study was designed in which the cases were infants who had died of sudden infant death syndrome (SIDS) in South Australia between January 1974 and December 1997, who were found not prone, not bed sharing and with the head not covered. The controls were two infants for each case, born in the same year and found in the prone position (again not bed sharing and with the head not covered). RESULTS: Sudden unexpected death infancy is rare in non-prone infants with the head not covered. occurring on average twice a year in South Australia, where there are 18,000-21,000 births per year. In this group there was a higher percentage of infants with features associated with low socio-economic groups (teenage pregnancies and maternal smoking), sibling SIDS, suspicion of non-accidental injury and the presence of minor congenital anomalies, especially cardiac anomalies. CONCLUSIONS: The majority of unexpected deaths in infancy can be prevented by not allowing infants to be unobserved in prone position, and by preventing them from getting their faces covered. For the few infants not found in these positions, a careful investigation should be made for malformations or non-accidental injury.     

Prone versus supine sleep position: a review of the physiological studies in SIDS research

A number of physiological studies, published over the last 10 years, have investigated the links between prone sleeping and sudden infant death syndrome (SIDS). This review evaluates those studies and derives an overview of the different affects of sleeping prone or supine in infancy. Generally, compared with the supine, the prone position raises arousal and wakening thresholds, promotes sleep and reduces autonomic activity through decreased parasympathetic activity, decreased sympathetic activity or an imbalance between the two systems. In addition, resting ventilation and ventilatory drive is improved in preterm infants, but in older infants (>1 month), there is no improvement in ventilation, and in 3-month-old infants, the position is adverse in terms of poorer ventilatory drive (in active sleep only). The majority of findings suggest a reduction in physiological control related to respiratory, cardiovascular and autonomic control mechanisms, including arousal during sleep in the prone position. Since the majority of these findings are from studies of healthy infants, continued reinforcement of the supine sleep recommendations for all infants is emphasized.     

Sudden infant death syndrome risk questionnaire: a mirror of parental awareness rather than a prospective diagnostic tool

AIM: In 1989, a scoring system that aimed to identify infants at risk of sudden infant death syndrome (SIDS) by a structured questionnaire [SIDS risk questionnaire (SRQ)] consisting of 25 items was introduced in Styria (Austria). It was the aim of the study to compare SIDS rates in the population that had access to the SRQ with the population that had no access. Furthermore, for the population receiving the SRQ, the responding (compliant) and non-responding (non-compliant) groups were compared concerning the incidence of SIDS. METHODS: Within the study period, 53 865 births and 57 SIDS cases were recorded (incidence 1.06/1000) and analysed retrospectively. RESULTS: The incidence of SIDS was significantly higher in the non-responding population (2.36/ 1000) than in the responding group (0.81/1000, p < 0.001). However, the incidence of SIDS was not significantly different in the population that had access to the risk questionnaire (1.29/1000) and the group without access (0.86/1000, p = 0.145). CONCLUSION: The value of any questionnaire used for SIDS prevention may be limited by the existence of a non-compliant population which represents a risk group and should be targeted by other preventive measures.     

Arterial oxygen saturation in infants at risk of sudden death: influence of sleeping position

To study the possible influence of sleeping position on arterial oxygen saturation, measured by pulse oximetry (Sp6₂), 7–h overnight recordings of breathing movements and ECG were performed in 43 infants (median age 2.4 months, range 0.2–11 months) at increased risk of sudden infant death syndrome (SIDS). Infants were randomly allocated to start sleeping either in their usual sleeping position or in the opposite position. After 3.5 h, all infants were gently turned over. Thus, each infant served as their own control. Recordings were analysed for sleep time, baseline Sp0₂ (only during regular breathing), and the number and duration of desaturations (a decrease in Sp0₂ to ≤80%). In the prone position, a significantly higher proportion of time was spent asleep (median 79% versus 70%; p < 0.05). Median baseline Sp0₂ was 98.8% (91.7–100%) in the prone and 99.0% (92.0–100%) in the supine position (ns). A total of 191 desaturations were found in 29 recordings; 96 in the prone and 95 in the supine position (ns). One infant subsequently died of SIDS while sleeping in the prone position. He had a relatively high number of desaturations (n = 12) which all occurred in the prone position. These results confirm earlier studies which could not find a significant influence of sleeping position on baseline oxygenation. The occurrence of desaturations in the prone position only in the infant who subsequently died requires further investigation.