A scientific review of the association between prone sleeping position and sudden infant death syndrome

A meeting was held in Canberra on 29 and 30 July 1991 to discuss the relationship between prone sleeping position and sudden infant death syndrome (SIDS). It was sponsored by the Australian Rotary Health Research Fund in association with the Sir Robert Menzies Memorial Foundation. The catalyst for the meeting was the recent paper in the Lancet reporting the results of the prospective study carried out by the Menzies Centre for Population Health Research in Hobart which reported an increased risk of SIDS for infants sleeping prone.     

The prone sleeping position impairs arousability in term infants

OBJECTIVE: To investigate whether the prone sleeping position impaired arousal from sleep in healthy infants and whether this impairment was related to cardiorespiratory variables, temperature, or age.Study design: Healthy term infants (n = 24) were studied with daytime polysomnography on 3 occasions: 2 to 3 weeks after birth, 2 to 3 months after birth, and 5 to 6 months after birth. Multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep and quiet sleep when infants slept both prone and supine. RESULTS: Arousal thresholds were significantly higher in both active sleep and quiet sleep when infants slept prone at 2 to 3 weeks and 2 to 3 months, but not at 5 to 6 months. These increases were independent of any sleep position-related change in either rectal or abdominal skin temperature, respiratory rate, oxygen saturation, or heart rate. CONCLUSIONS: The prone position significantly impairs arousal from both active sleep and quiet sleep in healthy term infants. This impairment in arousability occurred with no clinically significant changes in cardiorespiratory variables or body temperature. Decreased arousability from sleep in the prone position provides an important insight into its role as a risk factor for sudden infant death syndrome.     

Arousal from sleep pathways are affected by the prone sleeping position and preterm birth: Preterm birth,prone sleeping and arousal from sleep

Objectives

Preterm infants exhibit depressed arousability from sleep when compared with term infants. As the final cortical element of the arousal process may be the most critical for survival, we hypothesized that the increased vulnerability of preterm infants to the Sudden Infant Death Syndrome (SIDS) could be explained by depressed cortical arousal (CA) responses. We evaluated the effects of preterm birth on stimulus-induced arousal processes in both the prone and supine sleeping positions.

Study design

10 healthy preterm infants were studied with daytime polysomnography, in both supine and prone sleeping positions, at 36 weeks gestational age, 2–4 weeks, 2–3 months and 5–6 months post-term corrected age. Sub-cortical activations and cortical arousals (CA) were expressed as proportions of total arousal responses. Preterm data were compared with data from 13 healthy term infants studied at the same corrected ages.

Results

In preterm infants increased CAs were observed in the prone position at all ages studied. Compared to term infants, preterm infants had significantly fewer CAs in QS when prone at 2–3 months of age and more CAs when prone at 2–4 weeks in AS. There were no differences in either sleep state when infants slept supine.

Conclusions

Prone sleeping promoted CA responses in healthy preterm infants throughout the first six months of post-term age. We have previously suggested that in term infants enhanced CA represents a critical protection against a potentially harmful situation; we speculate that for preterm-born infants the need for this protection is greater than in term infants.     

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.     

Prematurity,sleeping position and sudden infant death syndrome

Preterm birth and prone sleeping position significantly increase the risk of sudden infant death syndrome (SIDS). The reduced incidence of SIDS with supine sleeping has been well publicised, yet some prematurely born infants are slept prone at the high-risk age for SIDS. This may reflect inadequate educational targeting of high-risk groups and/or concerns about possible adverse effects of supine sleeping. In addition, parents may receive mixed messages about sleeping positions, as they witness their prematurely born infants being nursed prone on neonatal units, often for many weeks. In the neonatal period, the prone position improves oxygenation, tidal volume and compliance of preterm infants with respiratory distress. The limited data available suggest prone positioning is also beneficial for convalescent, preterm infants. Thus, it is not clear when the advantages of prone sleeping cease. Studies are required to determine when supine sleeping for prematurely born infants can safely be recommended and hence an unambiguous message given to parents.     

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.     

Sudden infant death syndrome and sleeping position in pre-term and low birth weight infants: an opportunity for targeted intervention

Aims

To determine the combined effects of sudden infant death syndrome (SIDS) risk factors in the sleeping environment for infants who were “small at birth” (pre‐term (<37 weeks), low birth weight (<2500 g), or both).

Methods

A three year population based, case‐control study in five former health regions in England (population 17.7 million) with 325 cases and 1300 controls. Parental interviews were carried out after each death and reference sleep of age matched controls.

Results

Of the SIDS infants, 26% were “small at birth” compared to 8% of the controls. The most common sleeping position was supine, for both controls (69%) and those SIDS infants (48%) born at term or ⩾2500 g, but for “small at birth” SIDS infants the commonest sleeping position was side (48%). The combined effect of the risk associated with being “small at birth” and factors in the infant sleeping environment remained multiplicative despite controlling for possible confounding in the multivariate model. This effect was more than multiplicative for those infants placed to sleep on their side or who shared the bed with parents who habitually smoked, while for those “small at birth” SIDS who slept in a room separate from the parents, the large combined effect showed evidence of a significant interaction. No excess risk was identified from bed sharing with non‐smoking parents for infants born at term or birth weight ⩾2500 g.

Conclusion

The combined effects of SIDS risk factors in the sleeping environment and being pre‐term or low birth weight generate high risks for these infants. Their longer postnatal stay allows an opportunity to target parents and staff with risk reduction messages.     

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.     

Sudden infant death syndrome and sleeping position in pre-term and low birth weight infants: an opportunity for targeted intervention.

AIMS: To determine the combined effects of sudden infant death syndrome (SIDS) risk factors in the sleeping environment for infants who were "small at birth" (pre-term (<37 weeks), low birth weight (<2500 g), or both). METHODS: A three year population based, case-control study in five former health regions in England (population 17.7 million) with 325 cases and 1300 controls. Parental interviews were carried out after each death and reference sleep of age matched controls. RESULTS: Of the SIDS infants, 26% were "small at birth" compared to 8% of the controls. The most common sleeping position was supine, for both controls (69%) and those SIDS infants (48%) born at term or > or =2500 g, but for "small at birth" SIDS infants the commonest sleeping position was side (48%). The combined effect of the risk associated with being "small at birth" and factors in the infant sleeping environment remained multiplicative despite controlling for possible confounding in the multivariate model. This effect was more than multiplicative for those infants placed to sleep on their side or who shared the bed with parents who habitually smoked, while for those "small at birth" SIDS who slept in a room separate from the parents, the large combined effect showed evidence of a significant interaction. No excess risk was identified from bed sharing with non-smoking parents for infants born at term or birth weight > or =2500 g. CONCLUSION: The combined effects of SIDS risk factors in the sleeping environment and being pre-term or low birth weight generate high risks for these infants. Their longer postnatal stay allows an opportunity to target parents and staff with risk reduction messages.     

The healthy human infant tends to sleep in the prone rather than the supine position

There are few reports about developmental behavior relating to roll over among healthy infants. We assessed the relationship between the placed position on sleeping and altered sleeping position the next morning by roll over among healthy infants. A health check-up clinic distributed a total of 1626 questionnaires to parents whose infant's ages are 1.5 years (or 18 months) old. The age at the first roll over and the change in sleeping position the next morning after they started to roll over, were investigated. The mean age of roll over from the supine to the prone among infants who were placed mainly in the prone sleeping position, at least in the first week of life, was 4.0 months (S.D., 1.1). The mean age of roll over from the supine to the prone among infants who were placed mainly in the supine sleeping position during early neonatal life and thereafter was 4.4 months (S.D., 1.2). The age of the first roll over from supine to prone was significantly younger in infants who were placed mainly in the prone sleeping position during early neonatal life. Among 651 infants who had been placed supine, 34.7% were found prone by roll over the next morning. Among 211 infants who had been placed prone, 14.2% were found supine by roll over the next morning. The number of infants who rolled over from supine to prone position was statistically greater than those from prone to supine. It is likely that the healthy human infant tends to sleep in the prone rather than the supine position. The finding is especially important for the correct assessment of the position in which SIDS cases were found dead.     

Reduced arousals following obstructive apneas in infants sleeping prone

A decreased arousability and an increased risk for sudden infant death syndrome (SIDS) have been shown in infants sleeping prone. Obstructive apnea, a known risk factor for SIDS, is less often terminated by an arousal reaction in infants than in adults. The effect of body position on the arousal reaction to spontaneous respiratory events had not been previously studied in infants. The aim of our study was to see if body position has an influence on the frequency and delay of the arousal reaction to obstructive apnea. All obstructive events recorded during two successive nights in 20 infants sleeping one night prone and one night supine were studied. During the supine recording 153 obstructive events were detected, and 217 were detected during the prone session. Prone sleep was not associated with an increased frequency of obstructive apneas. Total sleep time was 382 min (range, 283-456) supine and 423 min (range, 325-521) prone (p = 0.003). Obstructive events duration was 6.5 s (range, 3-21.5) when sleeping supine and 8 s (range, 3.5-30.5) when prone (p = 0.002). Behavioral arousal were found in 57.5 % of obstructive events recorded supine and in 31.3 % of those seen prone (p < 0.001). Arousal occurred after 8 s (range, 0-21) from the start of the obstructions when supine and 10.5 s (range, 3.5-23.5) when prone (p = 0.001). Sighs were found in 34 % of supine obstructive events and in 44.7 % of those prone (p = 0.040). A reaction, i.e. arousal or sigh, was found in 91.5 % of supine events and 76 % of those prone (p < 0.001). We conclude that when sleeping supine, infants arouse to obstructive events more often and after shorter delay than when prone.     

Parental post-traumatic reactions after premature birth: implications for sleeping and eating problems in the infant

BACKGROUND: Progress in perinatal medicine has made it possible to increase the survival of very or extremely low birthweight infants. Developmental outcomes of surviving preterm infants have been analysed at the paediatric, neurological, cognitive, and behavioural levels, and a series of perinatal and environmental risk factors have been identified. The threat to the child's survival and invasive medical procedures can be very traumatic for the parents. Few empirical reports have considered post-traumatic stress reactions of the parents as a possible variable affecting a child's outcome. Some studies have described sleeping and eating problems as related to prematurity; these problems are especially critical for the parents. OBJECTIVE: To examine the effects of post-traumatic reactions of the parents on sleeping and eating problems of the children. DESIGN: Fifty families with a premature infant (25-33 gestation weeks) and a control group of 25 families with a full term infant participated in the study. Perinatal risks were evaluated during the hospital stay. Mothers and fathers were interviewed when their children were 18 months old about the child's problems and filled in a perinatal post-traumatic stress disorder questionnaire (PPQ). RESULTS: The severity of the perinatal risks only partly predicts a child's problems. Independently of the perinatal risks, the intensity of the post-traumatic reactions of the parents is an important predictor of these problems. CONCLUSIONS: These findings suggest that the parental response to premature birth mediates the risks of later adverse outcomes. Preventive intervention should be promoted.     

Effect of prone sleeping on circulatory control in infants.

BACKGROUND: The mechanism of death in sudden infant death syndrome (SIDS) remains unclear. Progressive bradycardia is the pre-eminent terminal event, suggesting that circulatory failure might be a crucial factor. Vasomotor tone regulates the circulatory system by controlling blood volume distribution while maintaining venous return and blood pressure. AIM: To examine whether prone sleeping, the most consistently identified risk factor for SIDS, has a measurable influence on vasomotor/circulatory control. METHODS: 44 full term infants (mean age, 7.9 weeks) were studied during an overnight sleep. Recordings were made while the infants were horizontal and asleep in the supine and prone positions, and repeated after a head up tilt to 60 degrees, maintained for 30 minutes, while in both sleep positions. Blood pressure, heart rate, anterior shin, and anterior abdominal wall skin temperatures were measured. RESULTS: Systolic blood pressure was lower, but peripheral skin temperature and heart rate were higher during sleep, while horizontal, in the prone rather than the supine position. After tilting, there was a greater reduction in blood pressure and a greater increase in peripheral skin temperature and heart rate when in the prone position. Anterior abdominal wall skin temperature did not vary in either sleeping positions while horizontal or tilted. CONCLUSION: Prone sleeping has a measurable effect on circulatory control, with a reduction in vasomotor tone resulting in peripheral vasodilatation, a higher peripheral skin temperature, a lower blood pressure, and a higher resting heart rate. Because vasomotor tone is crucially important in circulatory control this could be a factor in increasing the risk of SIDS.