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Ruth Gilbert, Georgia Salanti, Melissa Harden, Sarah See, Infant sleeping position and the sudden infant death syndrome: systematic review of observational studies and historical review of recommendations from 1940 to 2002, International Journal of Epidemiology, Volume 34, Issue 4, August 2005, Pages 874–887, https://doi.org/10.1093/ije/dyi088
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Abstract
Background Before the early 1990s, parents were advised to place infants to sleep on their front contrary to evidence from clinical research.
Methods We systematically reviewed associations between infant sleeping positions and sudden infant death syndrome (SIDS), explored sources of heterogeneity, and compared findings with published recommendations.
Results By 1970, there was a statistically significantly increased risk of SIDS for front sleeping compared with back (pooled odds ratio (OR) 2.93; 95% confidence interval (CI) 1.15, 7.47), and by 1986, for front compared with other positions (five studies, pooled OR 3.00; 1.69–5.31). The OR for front vs the back position was reduced as the prevalence of the front position in controls increased. The pooled OR for studies conducted before advice changed to avoid front sleeping was 2.95 (95% CI 1.69–5.15), and after was 6.91 (4.63–10.32). Sleeping on the front was recommended in books between 1943 and 1988 based on extrapolation from untested theory
Conclusions Advice to put infants to sleep on the front for nearly a half century was contrary to evidence available from 1970 that this was likely to be harmful. Systematic review of preventable risk factors for SIDS from 1970 would have led to earlier recognition of the risks of sleeping on the front and might have prevented over 10 000 infant deaths in the UK and at least 50 000 in Europe, the USA, and Australasia. Attenuation of the observed harm with increased adoption of the front position probably reflects a ‘healthy adopter’ phenomenon in that families at low risk of SIDS were more likely to adhere to prevailing health advice. This phenomenon is likely to be a general problem in the use of observational studies for assessing the safety of health promotion.
Sudden unexpected unexplained infant death, now known as sudden infant death syndrome (SIDS), was recognized as a major cause of infant death in the UK and USA throughout the 20th century. At the start of the 20th century, such deaths were attributed to overlying, particularly by drunken mothers.1 By the 1940s, as more deaths were investigated by autopsy, pathologists realized that few deaths were due to maternal overlying, and alternative mechanisms for ‘accidental mechanical suffocation’ were sought. In 1944, Abramson, a pathologist in New York State, noted that two-thirds of infants dying from mechanical suffocation were found face down, contrary to the usual sleeping position for infants at the time.2 His observations, which were corroborated by reports in the UK and Australia3,4 led to a health promotion campaign that recommended avoidance of the front position.5
The campaign was short-lived. In 1945, a paediatrician, Woolley, rejected Abramson's hypothesis of suffocation on the front based on experiments in which he had covered babies' faces with layers of blankets.6 He reported that the oxygen content of the air breathed by the babies only fell when they were covered with a rubber sheet and that babies moved if breathing was obstructed. He also criticized the explanation of suffocation because it ‘instilled guilt and self-incrimination in parents’.
Emergence of alternative explanations for death, such as unrecognized infection4,7,8 inhalation of vomit9 and hypersensitivity reaction to inhaled milk,10 further strengthened the argument against the suffocation hypothesis and highlighted the need for data on risk factors. The first published case–control study was started in 1956 in the USA,11 and in 1958, a similar study in the UK was the first to measure infant sleeping position in SIDS victims and live control babies.12 At around the same time, it became increasingly common to advocate sleeping on the front. We now know that front sleeping is a major cause of SIDS. We wanted to know whether systematic review of the evidence could have reversed this harmful advice sooner or whether variation in the association between sleeping on the front and SIDS was consistent with recommendations at the time. We did a systematic review and meta-analysis of the effect of front and side sleeping on the risk of SIDS, and an historical review of recommendations on infant sleeping position in books and pamphlets on infant care available in the UK between 1940 and 2002. We focussed on how the strength of the evidence for a harmful effect of front sleeping changed before and after advice changed in favour of avoidance of the front position. We hypothesized that the effect of the front position on SIDS might differ depending on whether health advice favoured front or not as families that adopt health advice are likely to be at lower risk of SIDS.
Methods
Historical review
We reviewed recommendations on infant sleeping position in books or pamphlets available in the UK from 1940 to 2002. We chose 1940 to include a period before the front position was widely advocated. We searched the Modern Medicine Collection at the Wellcome Trust library, and, because of a lack of more recent texts, the British Medical Association library from 1965 to 2002. We included any book or pamphlet that referred to the care of normal term infants aged <6 months, and mentioned infant sleeping position. Searches used the library indexing system for books on infant care and we also searched electronically using terms for paediatric, parent, and baby (details of search strategy available from authors).
One reviewer (S.S. or M.H.), assessed whether texts met the inclusion criteria and prepared a hard copy file with the extract and book title but not the date of publication. A second reviewer (R.G.) categorized the recommendation as favouring front, back, side, or non-front position(s), or neutral if all or none were implicitly or explicitly favoured. A second reviewer (S.S.), independently categorized one-third of the texts and there was complete agreement with the first reviewer.
Systematic review
We included any case–control or cohort study that compared the risk of SIDS in infants sleeping on their front, side, or back. Studies had to be based on SIDS infants and live healthy control infants from the same community. We searched for any comparative study of infant sleeping position and SIDS in MEDLINE (1966–2002) and EMBASE (1980–2002), using a detailed search strategy (available from the authors), and reference lists of review articles, a PhD thesis on the history of SIDS,13 and included studies. Abstracts were scanned by one reviewer (S.S., M.H., or R.G.), and full texts of potentially eligible studies retrieved. R.G. and S.P. jointly extracted data from included studies.
Data quality
We used data on the position in which the infant was placed to sleep before death or interview, or if lacking, data on usual position, or position found. If usual position was measured at multiple ages, we used results closest to 3 months of age. We recorded the method of selection of cases and controls, matching criteria, if any, and whether data collection methods differed in cases and controls.
Analysis
Our primary aim was to compare the risk of SIDS in infants sleeping front and back. As some studies did not separately report side and back positions, we also compared front with non-front positions. However, grouping side with back will attenuate the observed risk associated with the front position if the side position is also harmful. We therefore calculated odds ratios (ORs) for SIDS associated with sleeping front vs back, front vs non-front, and side vs back.
To avoid confounding, we used the unadjusted matched OR if reported. Otherwise we calculated the unmatched OR.14 Because studies differed in their design, populations, and methods, we used a random effects model in which it is assumed that the observed ORs are sampled from a common distribution around a mean effect with variance measured by the heterogeneity parameter. We estimated 95% confidence intervals (CIs) and considered a P-value <0.05 as statistically significant. Heterogeneity in the OR for SIDS was assessed by the chi-squared test (Q-test) and quantified using I2 which reflects the proportion of variation that is not due to sampling error.15 The possibility of publication bias was evaluated using funnel plots and the Egger and Begg tests.16,17
We determined the year at which there was a statistically significant association between front or side sleeping positions and SIDS by using a cumulative meta-analysis based on year of publication as described by Lau.18 The overall heterogeneity was used in the calculation of the CIs for the cumulative OR at every step using a random effects model. We applied recursive cumulative meta-analysis to examine the direction and magnitude of the relative changes in the cumulative evidence as a function of the cumulative sample size.19,20 At the end of every information period j, the ratio (cumulative ORj)/(cumulative ORj + 1) was assessed and compared with unity. If larger than one, this was interpreted as a ‘move’ of the evidence towards defining the front position as more harmful than in the previous information period.
To explore potential sources of heterogeneity we initially used conventional meta-regression to determine an association with variables previously suggested.21 In a univariate model, we first determined the effect of the position recorded in cases (before death, usual, or after death), year of publication, recruitment year (measured as the mid-point between start and end of recruitment), matching criteria for controls and cases, and country and continent of study. The combined effect on heterogeneity of the variables found to be significant in the univariate analysis was estimated in a multivariate meta-regression model. We extended the meta-regression analyses to examine the hypothesis that the prevalence of front sleeping in control infants is associated with heterogeneity. This is because parents who put their babies to sleep in the front position when advised not to, might have a different risk of SIDS than parents who do so when front sleeping is the norm (similarly for the side position).
The OR for front vs any other position can be written as using logOR = logitP(front|case) − logitP(front|control) and the prevalence of front sleeping is estimated in the controls as P(front) = P(front|control). Consequently, regression of logOR to P(front) will be biased by regression to the mean.
To overcome this we fitted a hierarchical model similar to that described by Thompson et al. to model background risk in randomized controlled trials.22,23 As the studies were case-control rather than trials, we made some modifications to the methods (see Appendix).
We retained in the model any factors that were statistically significantly associated with heterogeneity in the conventional meta-regression, and assessed the extent to which the factors included in the model explained the variation between studies by measuring the change in the heterogeneity parameter. If factors included in the model explained heterogeneity, the heterogeneity parameter (variance in the random effects) would be expected to get smaller. This model was fitted using Markov chain Monte Carlo methods within a Bayesian framework. The analysis was conducted using Intercooled Stata 8.2 (Stata Corp., College Station, TX), R 1.9.1 (R Foundation for statistical computing, Vienna) and Winbugs 1.4.1.
Results
Historical review
Table 1 summarizes the recommendations made in 83 texts that met the inclusion criteria (details available from the authors). From 1940 to the mid-1950s, texts favoured the back or side positions and only one, in 1943, recommended the front position. From 1954 until 1988, a substantial proportion of texts consistently favoured front sleeping, although many also favoured the side and back. The sudden shift in favour of front sleeping is best illustrated by ‘Baby and Child Care’ by Dr Benjamin Spock who recommended the back position in his 1955 edition, and the front position in 1956.24 In his 1958 edition, he argued ‘If he vomits, he's more likely to choke on the vomitus. Also, he tends to keep his head turned to the same side—usually toward the centre of the room. This may flatten the side of his head.’ Many authors repeated these arguments. Others argued that front sleeping reduced wind,25,26 coughing due to mucus,27 and made respiration easier.26 Suffocation was considered to be possible only if the baby was very weak.26 These views were not universal. In editions of his textbook in 1945, 1950, and 1959, Nelson stated that ‘position during sleep is relatively unimportant, but should be changed often to prevent moulding of the cranium’.28–30 Others were less equivocal. One author recommended in 1953, ‘Sleeping on his abdomen never should be permitted because of the danger of suffocating’.31 In 1966, another warned ‘Very small babies should never be left alone lying on their tummies. This is an American fashion to strengthen the back, but we think the dangers of suffocation are not sufficiently remote to justify it.’32
No texts favoured the front position after 1988. From the mid-1950s to 1990, many texts continued to recommend the side position, but few advocated sleeping on the back. In the early 1990s, most texts recommended the side position or simply advised against front sleeping, but apart from one text in 1990, the back position was not consistently advocated until 1995.
Systematic review
Of the 2897 abstracts scanned, and the 206 full text articles retrieved, 40 studies met the inclusion criteria (Figure 1 and Table 2). Four further studies were excluded (Figure 1). No randomized controlled trials were found. All 40 included studies provided data on front vs non-front positions, but only 24 studies separately recorded back and side positions. Of the 40 studies, 23 (and 15/24 reporting side and back positions) included some degree of matching of controls with cases. Of these, unadjusted matched ORs were available for 9/23 studies (and for 7/15 reporting side and back positions).33,33–44 For one study, we derived pooled ORs from data reported for separate ethnic groups.37 All studies were case–control except for one cohort study reported in two stages. This resulted in data for 2 years of the study (15 SIDS victims) being included twice in the cumulative meta-analyses.45,46 Repeated use of the same data was avoided for all the other studies except for Mitchell 2 1999 (details in Table 2). No substantial evidence was found for publication bias for any of the sleeping position comparisons either by examining the funnel plots or applying the Egger or Begg tests (lowest P-value = 0.103).
Author, year published . | Study period, selection of cases and controls, and method of data collection . | Position recordedd . | Back (%) . | Front (%) . | Total studied . |
---|---|---|---|---|---|
Carpenter 196512a | 1958–1961. SIDS: Referred to coroner in 12 London boroughs (aged 2 weeks–2 years, 6 of 100 SIDS victims were aged >12 months). Position found recorded by coroner. | 3 | 20 | 25 | 107 |
Controls: matched for age, sex and community from register of Medical Officer of Health. Sleeping position recorded by health visitors. | 2 | 45 | 11 | 183 | |
Froggatt 197057 | 1965–1967. SIDS: Consecutive cases in northern Ireland. | 2 | 11 | 7 | 139 |
Controls: matched for age, sex, and administrative area. | 2 | 35 | 4 | 143 | |
Data collection by home interviews in both cases and controls | |||||
Beal 1 198662 | 1970–1984. SIDS: South Australia interviewed within weeks of death by Beal. | 2 | 8 | 85 | 133 |
Controls: postal survey of 200 consecutive birth registrations in August 1984. | 2 | 23 | 39 | 152 | |
Tonkin 1 198661 | 1972–1982. SIDS: position found routinely recorded in Auckland, New Zealand in 1972, 1973, and 1982. | 3 | 9 | 56 | 91 |
Controls: Plunket nurses (health visitors) in Auckland noted sleeping position of 50 babies most recently seen (10 nurses in 1972, 15 nurses in 1973). In 1982 all nurses noted sleeping position of 2 week old babies during a 3 month period. | 5 | 4 | 29 | 1982 | |
Cameron 198659 | 1980–1982. SIDS: within the Melbourne statistical division, Australia. | 2 | 69 | 208 | |
Controls: matched by age and same hospital of birth. | 2 | 41 | 393 | ||
Data collection by home interviews in both groups. | |||||
Senecal 198793 | 1984–1985. SIDS: in the Departement d'Ille et Vilaine, France. | 1 | 85 | 20 | |
No details on how data were collected. | |||||
Controls: Infants born in 7 maternity hospitals in Brittany attending routine post-natal surveillance. Questionnaire completed by doctor at consultation. | 2 | 29 | 318 | ||
Nicholl 198833 | 1976–1979. SIDS: UK multicentre study. SIDS resident within local areas. | 2 | 42 | 265 | |
Controls: matched for age and area. | 2 | 25 | 273 | ||
Data collection by home interviews in both groups. | |||||
McGlashan 198958 | 1980–1986. SIDS: notified by coroners in Tasmania. | 2 | 5 | 59 | 164 |
Controls: matched for age, sex, and hospital of birth. Data collection at home interviews in both groups. | 2 | 10 | 43 | 329 | |
Beal 2 199194 | 1985–1989. SIDS: in South Australia interviewed within weeks of death by Beal. | 2 | 80 | 100 | |
Controls: postal survey of 200 consecutive birth registrations in August in 1988. | 2 | 29 | 182 | ||
Jonge 198963 | 1980–1986. SIDS: deaths in The Netherlands. | 2 | 86 | 142 | |
Data collected by home interview Controls: Infants at 17 well-baby clinics. Parents interviewed about sleeping position at 2–4 months and 5–7 months. | 2 | 62 | 320 | ||
Tonkin 2 198964,65 | 1981–1985. SIDS: deaths in Auckland, New Zealand. | 1 | 13 | 54 | 126 |
Data collected at interview. Controls: surveyed by plunket nurses in Auckland in 1983 aged 1–4 months. Results used for usual position at 3 months. | 2 | 8 | 51 | 1138 | |
Lee 198895 | 1986–1987. SIDS: prospective surveillance of all SIDS deaths in Hong Kong. Data collected at home interview | 2 | 56 | 44 | 16 |
Controls: age and sex matched, one from hospital and one from community. No details given on data collection. | 2 | 94 | 6 | 32 | |
Fleming 1 199034 | 1987–1989. SIDS: all SIDS in Avon, UK, interviewed at home within days of death. | 2 | 1 | 93 | 67 |
Controls: matched by age and area based on same health visitor list as SIDS victim. Data collection at home interview for both groups. | 2 | 18 | 58 | 131 | |
Bouvier-Colle 199096 | Study period not stated. SIDS: study in France, reported only in conference proceedings. | 3 | 88 | 782 | |
Controls: no details available on selection or data collection. | 2 | 34 | 211 | ||
Hoffman 199284 | 1978–1979. SIDS: All SIDS in six geographically defined areas in the USA. | 2 | 81 | 757 | |
Controls: matched for age, and study centre (second controls matched for ethnic group and birth weight not used in this review). Both SIDS and control parents were interviewed about usual sleeping position in the 2 weeks before death or interview. | 2 | 72 | 757 | ||
Engelberts 199183 | 1985–1987. SIDS: all deaths in The Netherlands. Data collection by parent-completed postal questionnaire after telephone contact. | 2 | 4 | 59 | 105 |
Controls: randomly selected from municipal registers. Data collection by postal questionnaire asking about usual sleeping position in each of months 1–6. Data for month 3 used in analyses. | 2 | 3 | 39 | 566 | |
Mitchell 1 199197 | 1987–1988. SIDS: deaths within areas covering 80% of births in New Zealand. | 1 | 73 | 128 | |
Controls: randomly selected in proportion to hospital births in same areas and frequency matched for predicted age and season of cases. Home interviews for both groups measuring position placed at nominated sleep. | 1 | 43 | 503 | ||
Dwyer 1 199145 | 1988–1990. SIDS: prospective cohort study of births in highest scoring quintile of risk score for SIDS in Tasmania. | 2 | 0 | 60 | 15 |
Controls: whole cohort excluding SIDS victims. Usual sleeping position prospectively recorded in SIDS and controls at 1 month of age. | 2 | 5 | 33 | 2534 | |
Wigfield 199290 | 1989–1990. SIDS: all deaths in Avon, UK after local publicity about adverse effects of front sleeping. | 1 | 81 | 32 | |
Controls: controls selected from same health visitor list as SIDS victim, matched by age and area. | 1 | 28 | 64 | ||
Data collection by home interview within days of death in both groups. | |||||
Ponsonby 199335 | 1988–1991. SIDS: all SIDS in Tasmania eligible for inclusion. | 2 | 67 | 58 | |
Controls: for each case one control matched for age, and one matched for age and birth weight. | 2 | 30 | 119 | ||
Data collection by home interviews for both cases and controls. Matched analyses used. | |||||
Jorch 199498 | 1990–1992. SIDS: cases in two districts in Germany. | 1 | 9 | 74 | 94 |
Data collected at home interview. Controls: postal survey in two districts of representative sample in Autumn 1991. | 1 | 25 | 32 | 758 | |
Gormally 199499 | Study period not stated. SIDS: cases identified by the Sudden Infant Death Association in Ireland. Position recorded (usual, put down, found) not stated. | NK | 9 | 79 | 97 |
Controls: matched for sex and age from Rotunda Hospital records in Dublin. | NK | 27 | 26 | 98 | |
Data collection by postal questionnaires in both groups. | |||||
Anderson 1995100 | 1984–1992. SIDS: 58% of all SIDS in eastern Norway were enrolled in the study. Parents were sent a postal questionnaire after adverse publicity about front position in 1993. Asked about usual sleeping position between week 2 and death. | 2 | 78 | 143 | |
Controls: age, sex, and time matched from birth registry. Postal questionnaire survey conducted in 1993 after adverse publicity about front position. Parents were asked about usual sleeping position for their infants up to 9 years ago between the age of 2 week and death for SIDS, and 2 weeks and 1 year for controls. | 2 | 50 | 373 | ||
Markestad 1 199536 | 1987–1989. SIDS: cases in county of Hordaland (comprises 10% of births in Norway). | 1 | 78 | 40 | |
Controls: randomly selected for another study before 1990. Postal questionnaires sent to case and control parents. | 1 | 64 | 192 | ||
Klonoff–Cohen 199537b | 1989–1992. SIDS: cases in five health departments in southern California. | 2 | 7 | 67 | 193 |
Controls: matched by birth date, hospital of birth, sex, and race. | 2 | 10 | 68 | 190 | |
Data collection in both groups by telephone interview before adverse publicity about sleeping position. Control interviews conducted 3–6 months after case interviews. | |||||
Taylor 199638 | 1992–1994. SIDS: cases were residents in King County, USA. Medical examiners asked parents standard questions about sleep position within 48 hours of death. | 2 | 57 | 47 | |
Controls: randomly selected using birth certificates for babies born on same date as case. | 2 | 36 | 25 | 142 | |
Data about usual position in previous 2 weeks collected by telephone interview. | |||||
Fleming 2 199639 | 1993–1995. SIDS: deaths in three English regions. | 1 | 44 | 16 | 188 |
Controls: matched by age and area from same health visitor list as case. | 1 | 66 | 3 | 774 | |
Data collected at home interview in both groups. | |||||
Mitchell 3 1997101 | 1991–1993. SIDS: cases were all post-neonatal SIDS in New Zealand. | 2 | 10 | 13 | 63 |
Controls: randomly selected to be representative of all births. | 2 | 24 | 3 | 771 | |
Data for both groups was extracted from routine records recorded by plunket nurses at initial contact and at ∼2 months of age | |||||
Brooke 199742 | 1992–1995. SIDS: all SIDS in Scotland were eligible. | 2 | 31 | 9 | 133 |
Controls: matched for age, time, and same maternity unit. | 2 | 57 | 2 | 256 | |
Data collected at home visits for both groups. | |||||
Oyen 199744 | 1992–1995. SIDS: all cases in Norway, Denmark, and Sweden were eligible. | 1 | 13 | 54 | 238 |
Controls: matched for age, sex, same maternity ward, and time. Parents of both groups contacted soon after death of case. Unclear whether interview or postal survey. | 1 | 44 | 20 | 856 | |
Schellscheidt 199798,102 | 1993–1994. SIDS: cases in two districts in Germany. Follow-on study from Jorch 94.98 | 1 | 23 | 59 | 56 |
Controls: selected randomly from same paediatrician as cared for SIDS victim, matched for age and sex. Selection repeated if no response. | 1 | 39 | 11 | 156 | |
Data collection in both groups at home interview. | |||||
Kleeman 1998103 | 1986–1992. SIDS: identified by autopsy in Lower Saxony, Germany. | 3 | 86 | 140 | |
Data collection by structured interview with parents. | |||||
Controls: selected from population register same region. | |||||
Data collection by postal survey. | 3 | 51 | 688 | ||
Skadberg 199836,104 | 1990–1995. SIDS: cases in county of Hordaland (10% of births in Norway). Parents asked to complete questionnaire within weeks of death. | 1 | 58 | 26 | |
Controls: selected as 10th birth in the county. Data collected by postal questionnaire. | 1 | 5 | 616 | ||
L'Hoir 1998105 | 1995–1996. SIDS: cases in The Netherlands 1995–96 (part of ECAS41). | 1 | 53 | 23 | 71 |
Controls: selected from municipal register or from birth list of nearest large urban hospital, therefore matched for age and area. Data collection at home interview in both cases and controls. | 1 | 87 | 5 | 143 | |
Mitchell 2 1999106 | 1987–1990. SIDS: continuation of all New Zealand case–control study using same methods. Contains data from Mitchell 1.97 | 1 | 5 | 64 | 388 |
Controls: as previously reported in Mitchell 1.97 | 1 | 16 | 33 | 1584 | |
4 | |||||
Dwyer 2 199946 | 1988–1995. SIDS: cohort study in Tasmania, Australia, measuring usual sleeping position at 1 month of age. | 2 | 3 | 37 | 37 |
Controls: comparison cohort selected as highest scoring quintile using at risk score for SIDS. Includes data from Dwyer 1 1991107. | 2 | 6 | 14 | 9655 | |
Toro 2001108 | 1996–1998. SIDS: cases from forensic department in Budapest, Hungary, interviewed after autopsy. | NK | 61 | 18 | |
Controls: controls from primary care units in one district of Budapest, interviewed at regular health checks. No information on how selected but all healthy. Unknown which sleeping position recorded (usual, last placed, or found). | NK | 55 | 74 | ||
Hauck 200240 | 1993–1996. SIDS: cases were Chicago residents (USA). | 1 | 22 | 57 | 258 |
Controls: selected from the Chicago birth registry matched for maternal age, child's age, and birth weight. Groups of 20–40 controls selected and those responding first included. | 1 | 33 | 35 | 260 | |
Data collection at home interview for both cases and controls. | |||||
McGarvey 200343 | 1994–1998. SIDS: all cases reported to National SIDS register in Ireland. | 1 | 57 | 9 | 203 |
Controls: 4 controls randomly selected from birth register matched for geographical location and date of birth. | 1 | 61 | 2 | 622 | |
Data collection by home interview within 6 weeks of death or enrolment. | |||||
Carpenter 200441c | 1992–1996. SIDS: studies from 20 regions in Europe. Agreed definitions and pathology investigations and same questions on sleeping position. Cases prospectively identified between 1992–96. Only centres not previously published included in analyses39,43,44,102,105 | 1 | 25 | 46 | 106 |
Controls: 2 or more controls selected from birth registers or clinic lists to represent live infants of same age, in same area at the time. All analyses adjusted for age and study using unconditional logistic regression. | 1 | 39 | 19 | 228 | |
Data collection by interview within median time of 3 weeks for cases and controls. |
Author, year published . | Study period, selection of cases and controls, and method of data collection . | Position recordedd . | Back (%) . | Front (%) . | Total studied . |
---|---|---|---|---|---|
Carpenter 196512a | 1958–1961. SIDS: Referred to coroner in 12 London boroughs (aged 2 weeks–2 years, 6 of 100 SIDS victims were aged >12 months). Position found recorded by coroner. | 3 | 20 | 25 | 107 |
Controls: matched for age, sex and community from register of Medical Officer of Health. Sleeping position recorded by health visitors. | 2 | 45 | 11 | 183 | |
Froggatt 197057 | 1965–1967. SIDS: Consecutive cases in northern Ireland. | 2 | 11 | 7 | 139 |
Controls: matched for age, sex, and administrative area. | 2 | 35 | 4 | 143 | |
Data collection by home interviews in both cases and controls | |||||
Beal 1 198662 | 1970–1984. SIDS: South Australia interviewed within weeks of death by Beal. | 2 | 8 | 85 | 133 |
Controls: postal survey of 200 consecutive birth registrations in August 1984. | 2 | 23 | 39 | 152 | |
Tonkin 1 198661 | 1972–1982. SIDS: position found routinely recorded in Auckland, New Zealand in 1972, 1973, and 1982. | 3 | 9 | 56 | 91 |
Controls: Plunket nurses (health visitors) in Auckland noted sleeping position of 50 babies most recently seen (10 nurses in 1972, 15 nurses in 1973). In 1982 all nurses noted sleeping position of 2 week old babies during a 3 month period. | 5 | 4 | 29 | 1982 | |
Cameron 198659 | 1980–1982. SIDS: within the Melbourne statistical division, Australia. | 2 | 69 | 208 | |
Controls: matched by age and same hospital of birth. | 2 | 41 | 393 | ||
Data collection by home interviews in both groups. | |||||
Senecal 198793 | 1984–1985. SIDS: in the Departement d'Ille et Vilaine, France. | 1 | 85 | 20 | |
No details on how data were collected. | |||||
Controls: Infants born in 7 maternity hospitals in Brittany attending routine post-natal surveillance. Questionnaire completed by doctor at consultation. | 2 | 29 | 318 | ||
Nicholl 198833 | 1976–1979. SIDS: UK multicentre study. SIDS resident within local areas. | 2 | 42 | 265 | |
Controls: matched for age and area. | 2 | 25 | 273 | ||
Data collection by home interviews in both groups. | |||||
McGlashan 198958 | 1980–1986. SIDS: notified by coroners in Tasmania. | 2 | 5 | 59 | 164 |
Controls: matched for age, sex, and hospital of birth. Data collection at home interviews in both groups. | 2 | 10 | 43 | 329 | |
Beal 2 199194 | 1985–1989. SIDS: in South Australia interviewed within weeks of death by Beal. | 2 | 80 | 100 | |
Controls: postal survey of 200 consecutive birth registrations in August in 1988. | 2 | 29 | 182 | ||
Jonge 198963 | 1980–1986. SIDS: deaths in The Netherlands. | 2 | 86 | 142 | |
Data collected by home interview Controls: Infants at 17 well-baby clinics. Parents interviewed about sleeping position at 2–4 months and 5–7 months. | 2 | 62 | 320 | ||
Tonkin 2 198964,65 | 1981–1985. SIDS: deaths in Auckland, New Zealand. | 1 | 13 | 54 | 126 |
Data collected at interview. Controls: surveyed by plunket nurses in Auckland in 1983 aged 1–4 months. Results used for usual position at 3 months. | 2 | 8 | 51 | 1138 | |
Lee 198895 | 1986–1987. SIDS: prospective surveillance of all SIDS deaths in Hong Kong. Data collected at home interview | 2 | 56 | 44 | 16 |
Controls: age and sex matched, one from hospital and one from community. No details given on data collection. | 2 | 94 | 6 | 32 | |
Fleming 1 199034 | 1987–1989. SIDS: all SIDS in Avon, UK, interviewed at home within days of death. | 2 | 1 | 93 | 67 |
Controls: matched by age and area based on same health visitor list as SIDS victim. Data collection at home interview for both groups. | 2 | 18 | 58 | 131 | |
Bouvier-Colle 199096 | Study period not stated. SIDS: study in France, reported only in conference proceedings. | 3 | 88 | 782 | |
Controls: no details available on selection or data collection. | 2 | 34 | 211 | ||
Hoffman 199284 | 1978–1979. SIDS: All SIDS in six geographically defined areas in the USA. | 2 | 81 | 757 | |
Controls: matched for age, and study centre (second controls matched for ethnic group and birth weight not used in this review). Both SIDS and control parents were interviewed about usual sleeping position in the 2 weeks before death or interview. | 2 | 72 | 757 | ||
Engelberts 199183 | 1985–1987. SIDS: all deaths in The Netherlands. Data collection by parent-completed postal questionnaire after telephone contact. | 2 | 4 | 59 | 105 |
Controls: randomly selected from municipal registers. Data collection by postal questionnaire asking about usual sleeping position in each of months 1–6. Data for month 3 used in analyses. | 2 | 3 | 39 | 566 | |
Mitchell 1 199197 | 1987–1988. SIDS: deaths within areas covering 80% of births in New Zealand. | 1 | 73 | 128 | |
Controls: randomly selected in proportion to hospital births in same areas and frequency matched for predicted age and season of cases. Home interviews for both groups measuring position placed at nominated sleep. | 1 | 43 | 503 | ||
Dwyer 1 199145 | 1988–1990. SIDS: prospective cohort study of births in highest scoring quintile of risk score for SIDS in Tasmania. | 2 | 0 | 60 | 15 |
Controls: whole cohort excluding SIDS victims. Usual sleeping position prospectively recorded in SIDS and controls at 1 month of age. | 2 | 5 | 33 | 2534 | |
Wigfield 199290 | 1989–1990. SIDS: all deaths in Avon, UK after local publicity about adverse effects of front sleeping. | 1 | 81 | 32 | |
Controls: controls selected from same health visitor list as SIDS victim, matched by age and area. | 1 | 28 | 64 | ||
Data collection by home interview within days of death in both groups. | |||||
Ponsonby 199335 | 1988–1991. SIDS: all SIDS in Tasmania eligible for inclusion. | 2 | 67 | 58 | |
Controls: for each case one control matched for age, and one matched for age and birth weight. | 2 | 30 | 119 | ||
Data collection by home interviews for both cases and controls. Matched analyses used. | |||||
Jorch 199498 | 1990–1992. SIDS: cases in two districts in Germany. | 1 | 9 | 74 | 94 |
Data collected at home interview. Controls: postal survey in two districts of representative sample in Autumn 1991. | 1 | 25 | 32 | 758 | |
Gormally 199499 | Study period not stated. SIDS: cases identified by the Sudden Infant Death Association in Ireland. Position recorded (usual, put down, found) not stated. | NK | 9 | 79 | 97 |
Controls: matched for sex and age from Rotunda Hospital records in Dublin. | NK | 27 | 26 | 98 | |
Data collection by postal questionnaires in both groups. | |||||
Anderson 1995100 | 1984–1992. SIDS: 58% of all SIDS in eastern Norway were enrolled in the study. Parents were sent a postal questionnaire after adverse publicity about front position in 1993. Asked about usual sleeping position between week 2 and death. | 2 | 78 | 143 | |
Controls: age, sex, and time matched from birth registry. Postal questionnaire survey conducted in 1993 after adverse publicity about front position. Parents were asked about usual sleeping position for their infants up to 9 years ago between the age of 2 week and death for SIDS, and 2 weeks and 1 year for controls. | 2 | 50 | 373 | ||
Markestad 1 199536 | 1987–1989. SIDS: cases in county of Hordaland (comprises 10% of births in Norway). | 1 | 78 | 40 | |
Controls: randomly selected for another study before 1990. Postal questionnaires sent to case and control parents. | 1 | 64 | 192 | ||
Klonoff–Cohen 199537b | 1989–1992. SIDS: cases in five health departments in southern California. | 2 | 7 | 67 | 193 |
Controls: matched by birth date, hospital of birth, sex, and race. | 2 | 10 | 68 | 190 | |
Data collection in both groups by telephone interview before adverse publicity about sleeping position. Control interviews conducted 3–6 months after case interviews. | |||||
Taylor 199638 | 1992–1994. SIDS: cases were residents in King County, USA. Medical examiners asked parents standard questions about sleep position within 48 hours of death. | 2 | 57 | 47 | |
Controls: randomly selected using birth certificates for babies born on same date as case. | 2 | 36 | 25 | 142 | |
Data about usual position in previous 2 weeks collected by telephone interview. | |||||
Fleming 2 199639 | 1993–1995. SIDS: deaths in three English regions. | 1 | 44 | 16 | 188 |
Controls: matched by age and area from same health visitor list as case. | 1 | 66 | 3 | 774 | |
Data collected at home interview in both groups. | |||||
Mitchell 3 1997101 | 1991–1993. SIDS: cases were all post-neonatal SIDS in New Zealand. | 2 | 10 | 13 | 63 |
Controls: randomly selected to be representative of all births. | 2 | 24 | 3 | 771 | |
Data for both groups was extracted from routine records recorded by plunket nurses at initial contact and at ∼2 months of age | |||||
Brooke 199742 | 1992–1995. SIDS: all SIDS in Scotland were eligible. | 2 | 31 | 9 | 133 |
Controls: matched for age, time, and same maternity unit. | 2 | 57 | 2 | 256 | |
Data collected at home visits for both groups. | |||||
Oyen 199744 | 1992–1995. SIDS: all cases in Norway, Denmark, and Sweden were eligible. | 1 | 13 | 54 | 238 |
Controls: matched for age, sex, same maternity ward, and time. Parents of both groups contacted soon after death of case. Unclear whether interview or postal survey. | 1 | 44 | 20 | 856 | |
Schellscheidt 199798,102 | 1993–1994. SIDS: cases in two districts in Germany. Follow-on study from Jorch 94.98 | 1 | 23 | 59 | 56 |
Controls: selected randomly from same paediatrician as cared for SIDS victim, matched for age and sex. Selection repeated if no response. | 1 | 39 | 11 | 156 | |
Data collection in both groups at home interview. | |||||
Kleeman 1998103 | 1986–1992. SIDS: identified by autopsy in Lower Saxony, Germany. | 3 | 86 | 140 | |
Data collection by structured interview with parents. | |||||
Controls: selected from population register same region. | |||||
Data collection by postal survey. | 3 | 51 | 688 | ||
Skadberg 199836,104 | 1990–1995. SIDS: cases in county of Hordaland (10% of births in Norway). Parents asked to complete questionnaire within weeks of death. | 1 | 58 | 26 | |
Controls: selected as 10th birth in the county. Data collected by postal questionnaire. | 1 | 5 | 616 | ||
L'Hoir 1998105 | 1995–1996. SIDS: cases in The Netherlands 1995–96 (part of ECAS41). | 1 | 53 | 23 | 71 |
Controls: selected from municipal register or from birth list of nearest large urban hospital, therefore matched for age and area. Data collection at home interview in both cases and controls. | 1 | 87 | 5 | 143 | |
Mitchell 2 1999106 | 1987–1990. SIDS: continuation of all New Zealand case–control study using same methods. Contains data from Mitchell 1.97 | 1 | 5 | 64 | 388 |
Controls: as previously reported in Mitchell 1.97 | 1 | 16 | 33 | 1584 | |
4 | |||||
Dwyer 2 199946 | 1988–1995. SIDS: cohort study in Tasmania, Australia, measuring usual sleeping position at 1 month of age. | 2 | 3 | 37 | 37 |
Controls: comparison cohort selected as highest scoring quintile using at risk score for SIDS. Includes data from Dwyer 1 1991107. | 2 | 6 | 14 | 9655 | |
Toro 2001108 | 1996–1998. SIDS: cases from forensic department in Budapest, Hungary, interviewed after autopsy. | NK | 61 | 18 | |
Controls: controls from primary care units in one district of Budapest, interviewed at regular health checks. No information on how selected but all healthy. Unknown which sleeping position recorded (usual, last placed, or found). | NK | 55 | 74 | ||
Hauck 200240 | 1993–1996. SIDS: cases were Chicago residents (USA). | 1 | 22 | 57 | 258 |
Controls: selected from the Chicago birth registry matched for maternal age, child's age, and birth weight. Groups of 20–40 controls selected and those responding first included. | 1 | 33 | 35 | 260 | |
Data collection at home interview for both cases and controls. | |||||
McGarvey 200343 | 1994–1998. SIDS: all cases reported to National SIDS register in Ireland. | 1 | 57 | 9 | 203 |
Controls: 4 controls randomly selected from birth register matched for geographical location and date of birth. | 1 | 61 | 2 | 622 | |
Data collection by home interview within 6 weeks of death or enrolment. | |||||
Carpenter 200441c | 1992–1996. SIDS: studies from 20 regions in Europe. Agreed definitions and pathology investigations and same questions on sleeping position. Cases prospectively identified between 1992–96. Only centres not previously published included in analyses39,43,44,102,105 | 1 | 25 | 46 | 106 |
Controls: 2 or more controls selected from birth registers or clinic lists to represent live infants of same age, in same area at the time. All analyses adjusted for age and study using unconditional logistic regression. | 1 | 39 | 19 | 228 | |
Data collection by interview within median time of 3 weeks for cases and controls. |
NK; not known.
The results for side, back and front positions were published in 1972 as a histogram.89 Actual figures have been supplied by the author.
Studies after this point included populations advised to avoid front sleeping. Four studies were excluded67,109–111
Data for separate centres provided by the author and then pooled.
1 = position placed to sleep before death or interview; 2 = usual position; 3 = position found.
Author, year published . | Study period, selection of cases and controls, and method of data collection . | Position recordedd . | Back (%) . | Front (%) . | Total studied . |
---|---|---|---|---|---|
Carpenter 196512a | 1958–1961. SIDS: Referred to coroner in 12 London boroughs (aged 2 weeks–2 years, 6 of 100 SIDS victims were aged >12 months). Position found recorded by coroner. | 3 | 20 | 25 | 107 |
Controls: matched for age, sex and community from register of Medical Officer of Health. Sleeping position recorded by health visitors. | 2 | 45 | 11 | 183 | |
Froggatt 197057 | 1965–1967. SIDS: Consecutive cases in northern Ireland. | 2 | 11 | 7 | 139 |
Controls: matched for age, sex, and administrative area. | 2 | 35 | 4 | 143 | |
Data collection by home interviews in both cases and controls | |||||
Beal 1 198662 | 1970–1984. SIDS: South Australia interviewed within weeks of death by Beal. | 2 | 8 | 85 | 133 |
Controls: postal survey of 200 consecutive birth registrations in August 1984. | 2 | 23 | 39 | 152 | |
Tonkin 1 198661 | 1972–1982. SIDS: position found routinely recorded in Auckland, New Zealand in 1972, 1973, and 1982. | 3 | 9 | 56 | 91 |
Controls: Plunket nurses (health visitors) in Auckland noted sleeping position of 50 babies most recently seen (10 nurses in 1972, 15 nurses in 1973). In 1982 all nurses noted sleeping position of 2 week old babies during a 3 month period. | 5 | 4 | 29 | 1982 | |
Cameron 198659 | 1980–1982. SIDS: within the Melbourne statistical division, Australia. | 2 | 69 | 208 | |
Controls: matched by age and same hospital of birth. | 2 | 41 | 393 | ||
Data collection by home interviews in both groups. | |||||
Senecal 198793 | 1984–1985. SIDS: in the Departement d'Ille et Vilaine, France. | 1 | 85 | 20 | |
No details on how data were collected. | |||||
Controls: Infants born in 7 maternity hospitals in Brittany attending routine post-natal surveillance. Questionnaire completed by doctor at consultation. | 2 | 29 | 318 | ||
Nicholl 198833 | 1976–1979. SIDS: UK multicentre study. SIDS resident within local areas. | 2 | 42 | 265 | |
Controls: matched for age and area. | 2 | 25 | 273 | ||
Data collection by home interviews in both groups. | |||||
McGlashan 198958 | 1980–1986. SIDS: notified by coroners in Tasmania. | 2 | 5 | 59 | 164 |
Controls: matched for age, sex, and hospital of birth. Data collection at home interviews in both groups. | 2 | 10 | 43 | 329 | |
Beal 2 199194 | 1985–1989. SIDS: in South Australia interviewed within weeks of death by Beal. | 2 | 80 | 100 | |
Controls: postal survey of 200 consecutive birth registrations in August in 1988. | 2 | 29 | 182 | ||
Jonge 198963 | 1980–1986. SIDS: deaths in The Netherlands. | 2 | 86 | 142 | |
Data collected by home interview Controls: Infants at 17 well-baby clinics. Parents interviewed about sleeping position at 2–4 months and 5–7 months. | 2 | 62 | 320 | ||
Tonkin 2 198964,65 | 1981–1985. SIDS: deaths in Auckland, New Zealand. | 1 | 13 | 54 | 126 |
Data collected at interview. Controls: surveyed by plunket nurses in Auckland in 1983 aged 1–4 months. Results used for usual position at 3 months. | 2 | 8 | 51 | 1138 | |
Lee 198895 | 1986–1987. SIDS: prospective surveillance of all SIDS deaths in Hong Kong. Data collected at home interview | 2 | 56 | 44 | 16 |
Controls: age and sex matched, one from hospital and one from community. No details given on data collection. | 2 | 94 | 6 | 32 | |
Fleming 1 199034 | 1987–1989. SIDS: all SIDS in Avon, UK, interviewed at home within days of death. | 2 | 1 | 93 | 67 |
Controls: matched by age and area based on same health visitor list as SIDS victim. Data collection at home interview for both groups. | 2 | 18 | 58 | 131 | |
Bouvier-Colle 199096 | Study period not stated. SIDS: study in France, reported only in conference proceedings. | 3 | 88 | 782 | |
Controls: no details available on selection or data collection. | 2 | 34 | 211 | ||
Hoffman 199284 | 1978–1979. SIDS: All SIDS in six geographically defined areas in the USA. | 2 | 81 | 757 | |
Controls: matched for age, and study centre (second controls matched for ethnic group and birth weight not used in this review). Both SIDS and control parents were interviewed about usual sleeping position in the 2 weeks before death or interview. | 2 | 72 | 757 | ||
Engelberts 199183 | 1985–1987. SIDS: all deaths in The Netherlands. Data collection by parent-completed postal questionnaire after telephone contact. | 2 | 4 | 59 | 105 |
Controls: randomly selected from municipal registers. Data collection by postal questionnaire asking about usual sleeping position in each of months 1–6. Data for month 3 used in analyses. | 2 | 3 | 39 | 566 | |
Mitchell 1 199197 | 1987–1988. SIDS: deaths within areas covering 80% of births in New Zealand. | 1 | 73 | 128 | |
Controls: randomly selected in proportion to hospital births in same areas and frequency matched for predicted age and season of cases. Home interviews for both groups measuring position placed at nominated sleep. | 1 | 43 | 503 | ||
Dwyer 1 199145 | 1988–1990. SIDS: prospective cohort study of births in highest scoring quintile of risk score for SIDS in Tasmania. | 2 | 0 | 60 | 15 |
Controls: whole cohort excluding SIDS victims. Usual sleeping position prospectively recorded in SIDS and controls at 1 month of age. | 2 | 5 | 33 | 2534 | |
Wigfield 199290 | 1989–1990. SIDS: all deaths in Avon, UK after local publicity about adverse effects of front sleeping. | 1 | 81 | 32 | |
Controls: controls selected from same health visitor list as SIDS victim, matched by age and area. | 1 | 28 | 64 | ||
Data collection by home interview within days of death in both groups. | |||||
Ponsonby 199335 | 1988–1991. SIDS: all SIDS in Tasmania eligible for inclusion. | 2 | 67 | 58 | |
Controls: for each case one control matched for age, and one matched for age and birth weight. | 2 | 30 | 119 | ||
Data collection by home interviews for both cases and controls. Matched analyses used. | |||||
Jorch 199498 | 1990–1992. SIDS: cases in two districts in Germany. | 1 | 9 | 74 | 94 |
Data collected at home interview. Controls: postal survey in two districts of representative sample in Autumn 1991. | 1 | 25 | 32 | 758 | |
Gormally 199499 | Study period not stated. SIDS: cases identified by the Sudden Infant Death Association in Ireland. Position recorded (usual, put down, found) not stated. | NK | 9 | 79 | 97 |
Controls: matched for sex and age from Rotunda Hospital records in Dublin. | NK | 27 | 26 | 98 | |
Data collection by postal questionnaires in both groups. | |||||
Anderson 1995100 | 1984–1992. SIDS: 58% of all SIDS in eastern Norway were enrolled in the study. Parents were sent a postal questionnaire after adverse publicity about front position in 1993. Asked about usual sleeping position between week 2 and death. | 2 | 78 | 143 | |
Controls: age, sex, and time matched from birth registry. Postal questionnaire survey conducted in 1993 after adverse publicity about front position. Parents were asked about usual sleeping position for their infants up to 9 years ago between the age of 2 week and death for SIDS, and 2 weeks and 1 year for controls. | 2 | 50 | 373 | ||
Markestad 1 199536 | 1987–1989. SIDS: cases in county of Hordaland (comprises 10% of births in Norway). | 1 | 78 | 40 | |
Controls: randomly selected for another study before 1990. Postal questionnaires sent to case and control parents. | 1 | 64 | 192 | ||
Klonoff–Cohen 199537b | 1989–1992. SIDS: cases in five health departments in southern California. | 2 | 7 | 67 | 193 |
Controls: matched by birth date, hospital of birth, sex, and race. | 2 | 10 | 68 | 190 | |
Data collection in both groups by telephone interview before adverse publicity about sleeping position. Control interviews conducted 3–6 months after case interviews. | |||||
Taylor 199638 | 1992–1994. SIDS: cases were residents in King County, USA. Medical examiners asked parents standard questions about sleep position within 48 hours of death. | 2 | 57 | 47 | |
Controls: randomly selected using birth certificates for babies born on same date as case. | 2 | 36 | 25 | 142 | |
Data about usual position in previous 2 weeks collected by telephone interview. | |||||
Fleming 2 199639 | 1993–1995. SIDS: deaths in three English regions. | 1 | 44 | 16 | 188 |
Controls: matched by age and area from same health visitor list as case. | 1 | 66 | 3 | 774 | |
Data collected at home interview in both groups. | |||||
Mitchell 3 1997101 | 1991–1993. SIDS: cases were all post-neonatal SIDS in New Zealand. | 2 | 10 | 13 | 63 |
Controls: randomly selected to be representative of all births. | 2 | 24 | 3 | 771 | |
Data for both groups was extracted from routine records recorded by plunket nurses at initial contact and at ∼2 months of age | |||||
Brooke 199742 | 1992–1995. SIDS: all SIDS in Scotland were eligible. | 2 | 31 | 9 | 133 |
Controls: matched for age, time, and same maternity unit. | 2 | 57 | 2 | 256 | |
Data collected at home visits for both groups. | |||||
Oyen 199744 | 1992–1995. SIDS: all cases in Norway, Denmark, and Sweden were eligible. | 1 | 13 | 54 | 238 |
Controls: matched for age, sex, same maternity ward, and time. Parents of both groups contacted soon after death of case. Unclear whether interview or postal survey. | 1 | 44 | 20 | 856 | |
Schellscheidt 199798,102 | 1993–1994. SIDS: cases in two districts in Germany. Follow-on study from Jorch 94.98 | 1 | 23 | 59 | 56 |
Controls: selected randomly from same paediatrician as cared for SIDS victim, matched for age and sex. Selection repeated if no response. | 1 | 39 | 11 | 156 | |
Data collection in both groups at home interview. | |||||
Kleeman 1998103 | 1986–1992. SIDS: identified by autopsy in Lower Saxony, Germany. | 3 | 86 | 140 | |
Data collection by structured interview with parents. | |||||
Controls: selected from population register same region. | |||||
Data collection by postal survey. | 3 | 51 | 688 | ||
Skadberg 199836,104 | 1990–1995. SIDS: cases in county of Hordaland (10% of births in Norway). Parents asked to complete questionnaire within weeks of death. | 1 | 58 | 26 | |
Controls: selected as 10th birth in the county. Data collected by postal questionnaire. | 1 | 5 | 616 | ||
L'Hoir 1998105 | 1995–1996. SIDS: cases in The Netherlands 1995–96 (part of ECAS41). | 1 | 53 | 23 | 71 |
Controls: selected from municipal register or from birth list of nearest large urban hospital, therefore matched for age and area. Data collection at home interview in both cases and controls. | 1 | 87 | 5 | 143 | |
Mitchell 2 1999106 | 1987–1990. SIDS: continuation of all New Zealand case–control study using same methods. Contains data from Mitchell 1.97 | 1 | 5 | 64 | 388 |
Controls: as previously reported in Mitchell 1.97 | 1 | 16 | 33 | 1584 | |
4 | |||||
Dwyer 2 199946 | 1988–1995. SIDS: cohort study in Tasmania, Australia, measuring usual sleeping position at 1 month of age. | 2 | 3 | 37 | 37 |
Controls: comparison cohort selected as highest scoring quintile using at risk score for SIDS. Includes data from Dwyer 1 1991107. | 2 | 6 | 14 | 9655 | |
Toro 2001108 | 1996–1998. SIDS: cases from forensic department in Budapest, Hungary, interviewed after autopsy. | NK | 61 | 18 | |
Controls: controls from primary care units in one district of Budapest, interviewed at regular health checks. No information on how selected but all healthy. Unknown which sleeping position recorded (usual, last placed, or found). | NK | 55 | 74 | ||
Hauck 200240 | 1993–1996. SIDS: cases were Chicago residents (USA). | 1 | 22 | 57 | 258 |
Controls: selected from the Chicago birth registry matched for maternal age, child's age, and birth weight. Groups of 20–40 controls selected and those responding first included. | 1 | 33 | 35 | 260 | |
Data collection at home interview for both cases and controls. | |||||
McGarvey 200343 | 1994–1998. SIDS: all cases reported to National SIDS register in Ireland. | 1 | 57 | 9 | 203 |
Controls: 4 controls randomly selected from birth register matched for geographical location and date of birth. | 1 | 61 | 2 | 622 | |
Data collection by home interview within 6 weeks of death or enrolment. | |||||
Carpenter 200441c | 1992–1996. SIDS: studies from 20 regions in Europe. Agreed definitions and pathology investigations and same questions on sleeping position. Cases prospectively identified between 1992–96. Only centres not previously published included in analyses39,43,44,102,105 | 1 | 25 | 46 | 106 |
Controls: 2 or more controls selected from birth registers or clinic lists to represent live infants of same age, in same area at the time. All analyses adjusted for age and study using unconditional logistic regression. | 1 | 39 | 19 | 228 | |
Data collection by interview within median time of 3 weeks for cases and controls. |
Author, year published . | Study period, selection of cases and controls, and method of data collection . | Position recordedd . | Back (%) . | Front (%) . | Total studied . |
---|---|---|---|---|---|
Carpenter 196512a | 1958–1961. SIDS: Referred to coroner in 12 London boroughs (aged 2 weeks–2 years, 6 of 100 SIDS victims were aged >12 months). Position found recorded by coroner. | 3 | 20 | 25 | 107 |
Controls: matched for age, sex and community from register of Medical Officer of Health. Sleeping position recorded by health visitors. | 2 | 45 | 11 | 183 | |
Froggatt 197057 | 1965–1967. SIDS: Consecutive cases in northern Ireland. | 2 | 11 | 7 | 139 |
Controls: matched for age, sex, and administrative area. | 2 | 35 | 4 | 143 | |
Data collection by home interviews in both cases and controls | |||||
Beal 1 198662 | 1970–1984. SIDS: South Australia interviewed within weeks of death by Beal. | 2 | 8 | 85 | 133 |
Controls: postal survey of 200 consecutive birth registrations in August 1984. | 2 | 23 | 39 | 152 | |
Tonkin 1 198661 | 1972–1982. SIDS: position found routinely recorded in Auckland, New Zealand in 1972, 1973, and 1982. | 3 | 9 | 56 | 91 |
Controls: Plunket nurses (health visitors) in Auckland noted sleeping position of 50 babies most recently seen (10 nurses in 1972, 15 nurses in 1973). In 1982 all nurses noted sleeping position of 2 week old babies during a 3 month period. | 5 | 4 | 29 | 1982 | |
Cameron 198659 | 1980–1982. SIDS: within the Melbourne statistical division, Australia. | 2 | 69 | 208 | |
Controls: matched by age and same hospital of birth. | 2 | 41 | 393 | ||
Data collection by home interviews in both groups. | |||||
Senecal 198793 | 1984–1985. SIDS: in the Departement d'Ille et Vilaine, France. | 1 | 85 | 20 | |
No details on how data were collected. | |||||
Controls: Infants born in 7 maternity hospitals in Brittany attending routine post-natal surveillance. Questionnaire completed by doctor at consultation. | 2 | 29 | 318 | ||
Nicholl 198833 | 1976–1979. SIDS: UK multicentre study. SIDS resident within local areas. | 2 | 42 | 265 | |
Controls: matched for age and area. | 2 | 25 | 273 | ||
Data collection by home interviews in both groups. | |||||
McGlashan 198958 | 1980–1986. SIDS: notified by coroners in Tasmania. | 2 | 5 | 59 | 164 |
Controls: matched for age, sex, and hospital of birth. Data collection at home interviews in both groups. | 2 | 10 | 43 | 329 | |
Beal 2 199194 | 1985–1989. SIDS: in South Australia interviewed within weeks of death by Beal. | 2 | 80 | 100 | |
Controls: postal survey of 200 consecutive birth registrations in August in 1988. | 2 | 29 | 182 | ||
Jonge 198963 | 1980–1986. SIDS: deaths in The Netherlands. | 2 | 86 | 142 | |
Data collected by home interview Controls: Infants at 17 well-baby clinics. Parents interviewed about sleeping position at 2–4 months and 5–7 months. | 2 | 62 | 320 | ||
Tonkin 2 198964,65 | 1981–1985. SIDS: deaths in Auckland, New Zealand. | 1 | 13 | 54 | 126 |
Data collected at interview. Controls: surveyed by plunket nurses in Auckland in 1983 aged 1–4 months. Results used for usual position at 3 months. | 2 | 8 | 51 | 1138 | |
Lee 198895 | 1986–1987. SIDS: prospective surveillance of all SIDS deaths in Hong Kong. Data collected at home interview | 2 | 56 | 44 | 16 |
Controls: age and sex matched, one from hospital and one from community. No details given on data collection. | 2 | 94 | 6 | 32 | |
Fleming 1 199034 | 1987–1989. SIDS: all SIDS in Avon, UK, interviewed at home within days of death. | 2 | 1 | 93 | 67 |
Controls: matched by age and area based on same health visitor list as SIDS victim. Data collection at home interview for both groups. | 2 | 18 | 58 | 131 | |
Bouvier-Colle 199096 | Study period not stated. SIDS: study in France, reported only in conference proceedings. | 3 | 88 | 782 | |
Controls: no details available on selection or data collection. | 2 | 34 | 211 | ||
Hoffman 199284 | 1978–1979. SIDS: All SIDS in six geographically defined areas in the USA. | 2 | 81 | 757 | |
Controls: matched for age, and study centre (second controls matched for ethnic group and birth weight not used in this review). Both SIDS and control parents were interviewed about usual sleeping position in the 2 weeks before death or interview. | 2 | 72 | 757 | ||
Engelberts 199183 | 1985–1987. SIDS: all deaths in The Netherlands. Data collection by parent-completed postal questionnaire after telephone contact. | 2 | 4 | 59 | 105 |
Controls: randomly selected from municipal registers. Data collection by postal questionnaire asking about usual sleeping position in each of months 1–6. Data for month 3 used in analyses. | 2 | 3 | 39 | 566 | |
Mitchell 1 199197 | 1987–1988. SIDS: deaths within areas covering 80% of births in New Zealand. | 1 | 73 | 128 | |
Controls: randomly selected in proportion to hospital births in same areas and frequency matched for predicted age and season of cases. Home interviews for both groups measuring position placed at nominated sleep. | 1 | 43 | 503 | ||
Dwyer 1 199145 | 1988–1990. SIDS: prospective cohort study of births in highest scoring quintile of risk score for SIDS in Tasmania. | 2 | 0 | 60 | 15 |
Controls: whole cohort excluding SIDS victims. Usual sleeping position prospectively recorded in SIDS and controls at 1 month of age. | 2 | 5 | 33 | 2534 | |
Wigfield 199290 | 1989–1990. SIDS: all deaths in Avon, UK after local publicity about adverse effects of front sleeping. | 1 | 81 | 32 | |
Controls: controls selected from same health visitor list as SIDS victim, matched by age and area. | 1 | 28 | 64 | ||
Data collection by home interview within days of death in both groups. | |||||
Ponsonby 199335 | 1988–1991. SIDS: all SIDS in Tasmania eligible for inclusion. | 2 | 67 | 58 | |
Controls: for each case one control matched for age, and one matched for age and birth weight. | 2 | 30 | 119 | ||
Data collection by home interviews for both cases and controls. Matched analyses used. | |||||
Jorch 199498 | 1990–1992. SIDS: cases in two districts in Germany. | 1 | 9 | 74 | 94 |
Data collected at home interview. Controls: postal survey in two districts of representative sample in Autumn 1991. | 1 | 25 | 32 | 758 | |
Gormally 199499 | Study period not stated. SIDS: cases identified by the Sudden Infant Death Association in Ireland. Position recorded (usual, put down, found) not stated. | NK | 9 | 79 | 97 |
Controls: matched for sex and age from Rotunda Hospital records in Dublin. | NK | 27 | 26 | 98 | |
Data collection by postal questionnaires in both groups. | |||||
Anderson 1995100 | 1984–1992. SIDS: 58% of all SIDS in eastern Norway were enrolled in the study. Parents were sent a postal questionnaire after adverse publicity about front position in 1993. Asked about usual sleeping position between week 2 and death. | 2 | 78 | 143 | |
Controls: age, sex, and time matched from birth registry. Postal questionnaire survey conducted in 1993 after adverse publicity about front position. Parents were asked about usual sleeping position for their infants up to 9 years ago between the age of 2 week and death for SIDS, and 2 weeks and 1 year for controls. | 2 | 50 | 373 | ||
Markestad 1 199536 | 1987–1989. SIDS: cases in county of Hordaland (comprises 10% of births in Norway). | 1 | 78 | 40 | |
Controls: randomly selected for another study before 1990. Postal questionnaires sent to case and control parents. | 1 | 64 | 192 | ||
Klonoff–Cohen 199537b | 1989–1992. SIDS: cases in five health departments in southern California. | 2 | 7 | 67 | 193 |
Controls: matched by birth date, hospital of birth, sex, and race. | 2 | 10 | 68 | 190 | |
Data collection in both groups by telephone interview before adverse publicity about sleeping position. Control interviews conducted 3–6 months after case interviews. | |||||
Taylor 199638 | 1992–1994. SIDS: cases were residents in King County, USA. Medical examiners asked parents standard questions about sleep position within 48 hours of death. | 2 | 57 | 47 | |
Controls: randomly selected using birth certificates for babies born on same date as case. | 2 | 36 | 25 | 142 | |
Data about usual position in previous 2 weeks collected by telephone interview. | |||||
Fleming 2 199639 | 1993–1995. SIDS: deaths in three English regions. | 1 | 44 | 16 | 188 |
Controls: matched by age and area from same health visitor list as case. | 1 | 66 | 3 | 774 | |
Data collected at home interview in both groups. | |||||
Mitchell 3 1997101 | 1991–1993. SIDS: cases were all post-neonatal SIDS in New Zealand. | 2 | 10 | 13 | 63 |
Controls: randomly selected to be representative of all births. | 2 | 24 | 3 | 771 | |
Data for both groups was extracted from routine records recorded by plunket nurses at initial contact and at ∼2 months of age | |||||
Brooke 199742 | 1992–1995. SIDS: all SIDS in Scotland were eligible. | 2 | 31 | 9 | 133 |
Controls: matched for age, time, and same maternity unit. | 2 | 57 | 2 | 256 | |
Data collected at home visits for both groups. | |||||
Oyen 199744 | 1992–1995. SIDS: all cases in Norway, Denmark, and Sweden were eligible. | 1 | 13 | 54 | 238 |
Controls: matched for age, sex, same maternity ward, and time. Parents of both groups contacted soon after death of case. Unclear whether interview or postal survey. | 1 | 44 | 20 | 856 | |
Schellscheidt 199798,102 | 1993–1994. SIDS: cases in two districts in Germany. Follow-on study from Jorch 94.98 | 1 | 23 | 59 | 56 |
Controls: selected randomly from same paediatrician as cared for SIDS victim, matched for age and sex. Selection repeated if no response. | 1 | 39 | 11 | 156 | |
Data collection in both groups at home interview. | |||||
Kleeman 1998103 | 1986–1992. SIDS: identified by autopsy in Lower Saxony, Germany. | 3 | 86 | 140 | |
Data collection by structured interview with parents. | |||||
Controls: selected from population register same region. | |||||
Data collection by postal survey. | 3 | 51 | 688 | ||
Skadberg 199836,104 | 1990–1995. SIDS: cases in county of Hordaland (10% of births in Norway). Parents asked to complete questionnaire within weeks of death. | 1 | 58 | 26 | |
Controls: selected as 10th birth in the county. Data collected by postal questionnaire. | 1 | 5 | 616 | ||
L'Hoir 1998105 | 1995–1996. SIDS: cases in The Netherlands 1995–96 (part of ECAS41). | 1 | 53 | 23 | 71 |
Controls: selected from municipal register or from birth list of nearest large urban hospital, therefore matched for age and area. Data collection at home interview in both cases and controls. | 1 | 87 | 5 | 143 | |
Mitchell 2 1999106 | 1987–1990. SIDS: continuation of all New Zealand case–control study using same methods. Contains data from Mitchell 1.97 | 1 | 5 | 64 | 388 |
Controls: as previously reported in Mitchell 1.97 | 1 | 16 | 33 | 1584 | |
4 | |||||
Dwyer 2 199946 | 1988–1995. SIDS: cohort study in Tasmania, Australia, measuring usual sleeping position at 1 month of age. | 2 | 3 | 37 | 37 |
Controls: comparison cohort selected as highest scoring quintile using at risk score for SIDS. Includes data from Dwyer 1 1991107. | 2 | 6 | 14 | 9655 | |
Toro 2001108 | 1996–1998. SIDS: cases from forensic department in Budapest, Hungary, interviewed after autopsy. | NK | 61 | 18 | |
Controls: controls from primary care units in one district of Budapest, interviewed at regular health checks. No information on how selected but all healthy. Unknown which sleeping position recorded (usual, last placed, or found). | NK | 55 | 74 | ||
Hauck 200240 | 1993–1996. SIDS: cases were Chicago residents (USA). | 1 | 22 | 57 | 258 |
Controls: selected from the Chicago birth registry matched for maternal age, child's age, and birth weight. Groups of 20–40 controls selected and those responding first included. | 1 | 33 | 35 | 260 | |
Data collection at home interview for both cases and controls. | |||||
McGarvey 200343 | 1994–1998. SIDS: all cases reported to National SIDS register in Ireland. | 1 | 57 | 9 | 203 |
Controls: 4 controls randomly selected from birth register matched for geographical location and date of birth. | 1 | 61 | 2 | 622 | |
Data collection by home interview within 6 weeks of death or enrolment. | |||||
Carpenter 200441c | 1992–1996. SIDS: studies from 20 regions in Europe. Agreed definitions and pathology investigations and same questions on sleeping position. Cases prospectively identified between 1992–96. Only centres not previously published included in analyses39,43,44,102,105 | 1 | 25 | 46 | 106 |
Controls: 2 or more controls selected from birth registers or clinic lists to represent live infants of same age, in same area at the time. All analyses adjusted for age and study using unconditional logistic regression. | 1 | 39 | 19 | 228 | |
Data collection by interview within median time of 3 weeks for cases and controls. |
NK; not known.
The results for side, back and front positions were published in 1972 as a histogram.89 Actual figures have been supplied by the author.
Studies after this point included populations advised to avoid front sleeping. Four studies were excluded67,109–111
Data for separate centres provided by the author and then pooled.
1 = position placed to sleep before death or interview; 2 = usual position; 3 = position found.
There was a statistically significantly higher risk of death associated with the front position whether compared with the back (Figure 2a) or non-front positions (Figure 2c). There was a weak association between the side position and the risk of SIDS, which was marginally worse than back (Figure 2e).
The cumulative meta-analyses showed that the association between death and the front position compared with back had become statistically significant by 1970, after the first two case–control studies (cumulated OR 2.93; 95%CI 1.15–7.47; Figure 2b). When front was compared with non-front, the association was not statistically significant until 1986, after inclusion of five studies (cumulated OR 3.00; 1.69–5.31; Figure 2d). Recursive meta-analysis showed that the relative magnitude of the cumulative OR for front vs back changed by up to 22% from one publication year to the next between 1986 and 1996, but remained stable (maximum change 4%) when studies published after 1996 were included (results not shown). After 1996, populations included in these studies were advised to use the side or back positions (see Table 2).
Substantial heterogeneity was detected in all three datasets as shown in the forest plots (Figures 2a, c, and e) and reflected in the highly significant Q statistic and high values for I2 (83% for front vs back, 89% for front vs non-front, and 73% for side vs back). In the conventional meta-regression the only significant factor was the year of recruitment, with later studies associated with an increased OR for SIDS in all three comparisons. The results of extending the meta-regression to include the prevalence of front or side positions in control babies are shown in Table 3. For front compared with back, the prevalence of the front position was the only factor that was significantly associated with heterogeneity. As the prevalence of the front position in control babies increased, the OR for SIDS decreased. For front vs non-front positions, there was little evidence that prevalence of front position or year of recruitment explained heterogeneity. Finally, in the comparison of side vs back, only the prevalence of the side position was associated with a reduction in the OR, but had little effect on heterogeneity.
Parameter . | Adjusted measure of effect (OR) . | 95% credibility interval . | Heterogeneity (95% credibility intervalb) . | Change in heterogeneity parameterc . | ||||
---|---|---|---|---|---|---|---|---|
Front vs back | ||||||||
Front vs back | 4.92 | 3.62–6.58 | 0.31 (0.10–0.71) | 0.47 | ||||
Prevalence of front position | 0.75 | 0.64–0.87 | ||||||
Midpoint of recruitment period | 1.03 | 1.00–1.07 | ||||||
Front vs non-front | ||||||||
Front vs non-front | 4.30 | 3.39–5.39 | 0.40 (0.21–0.71) | 0.07 | ||||
Prevalence of front position | 0.84 | 0.71–1.00 | ||||||
Midpoint of recruitment period | 1.04 | 1.01–1.07 | ||||||
Side vs back | ||||||||
Side vs back | 1.40 | 3.62–1.84 | 0.31 (0.11–0.70) | 0.002 | ||||
Prevalence of side position | 0.69 | 0.54–0.89 |
Parameter . | Adjusted measure of effect (OR) . | 95% credibility interval . | Heterogeneity (95% credibility intervalb) . | Change in heterogeneity parameterc . | ||||
---|---|---|---|---|---|---|---|---|
Front vs back | ||||||||
Front vs back | 4.92 | 3.62–6.58 | 0.31 (0.10–0.71) | 0.47 | ||||
Prevalence of front position | 0.75 | 0.64–0.87 | ||||||
Midpoint of recruitment period | 1.03 | 1.00–1.07 | ||||||
Front vs non-front | ||||||||
Front vs non-front | 4.30 | 3.39–5.39 | 0.40 (0.21–0.71) | 0.07 | ||||
Prevalence of front position | 0.84 | 0.71–1.00 | ||||||
Midpoint of recruitment period | 1.04 | 1.01–1.07 | ||||||
Side vs back | ||||||||
Side vs back | 1.40 | 3.62–1.84 | 0.31 (0.11–0.70) | 0.002 | ||||
Prevalence of side position | 0.69 | 0.54–0.89 |
Restricted to 38 case–control studies.
Credibility interval: there is a 95% probability that the true value lies within the 95% credibility interval.
Absolute reduction in between-study variance between the crude meta-analysis model and the meta-regression model.
Parameter . | Adjusted measure of effect (OR) . | 95% credibility interval . | Heterogeneity (95% credibility intervalb) . | Change in heterogeneity parameterc . | ||||
---|---|---|---|---|---|---|---|---|
Front vs back | ||||||||
Front vs back | 4.92 | 3.62–6.58 | 0.31 (0.10–0.71) | 0.47 | ||||
Prevalence of front position | 0.75 | 0.64–0.87 | ||||||
Midpoint of recruitment period | 1.03 | 1.00–1.07 | ||||||
Front vs non-front | ||||||||
Front vs non-front | 4.30 | 3.39–5.39 | 0.40 (0.21–0.71) | 0.07 | ||||
Prevalence of front position | 0.84 | 0.71–1.00 | ||||||
Midpoint of recruitment period | 1.04 | 1.01–1.07 | ||||||
Side vs back | ||||||||
Side vs back | 1.40 | 3.62–1.84 | 0.31 (0.11–0.70) | 0.002 | ||||
Prevalence of side position | 0.69 | 0.54–0.89 |
Parameter . | Adjusted measure of effect (OR) . | 95% credibility interval . | Heterogeneity (95% credibility intervalb) . | Change in heterogeneity parameterc . | ||||
---|---|---|---|---|---|---|---|---|
Front vs back | ||||||||
Front vs back | 4.92 | 3.62–6.58 | 0.31 (0.10–0.71) | 0.47 | ||||
Prevalence of front position | 0.75 | 0.64–0.87 | ||||||
Midpoint of recruitment period | 1.03 | 1.00–1.07 | ||||||
Front vs non-front | ||||||||
Front vs non-front | 4.30 | 3.39–5.39 | 0.40 (0.21–0.71) | 0.07 | ||||
Prevalence of front position | 0.84 | 0.71–1.00 | ||||||
Midpoint of recruitment period | 1.04 | 1.01–1.07 | ||||||
Side vs back | ||||||||
Side vs back | 1.40 | 3.62–1.84 | 0.31 (0.11–0.70) | 0.002 | ||||
Prevalence of side position | 0.69 | 0.54–0.89 |
Restricted to 38 case–control studies.
Credibility interval: there is a 95% probability that the true value lies within the 95% credibility interval.
Absolute reduction in between-study variance between the crude meta-analysis model and the meta-regression model.
Discussion
The front sleeping position was recommended from 1943 to 1988 although the first text to advise against front sleeping was not published until 1992. The safest position—on the back—was recommended sporadically during the 1980s but not consistently until 1995. However, by 1970 the pooled evidence from two studies showed that the risk of SIDS was statistically significantly higher for babies on the front than on the back. The harmful effect of front sleeping was lowest when the prevalence of the front position in control babies was highest.
A detailed historical analysis of why clinicians recommended that infants sleep on the front is beyond the scope of this study. From the reasons given for advocating front sleeping,47 there is no clear evidence that the back position increases the risk of crying,46,48–50 inhalation of vomit, or colic.46,50,51 However, in the short term, sleeping on the front is associated with increased motor development,52,53 rounder head shape,54 nappy rash,49,50 and pyloric stenosis.55 Front sleeping is also associated with longer sleep duration,46,48,50 probably by reducing physiological control of respiratory, cardiovascular and autonomic control mechanisms, and arousal during sleep.56
Our analyses identified five factors that may have contributed to the delayed recognition of the risks of front sleeping: the paucity of published studies between 1970 and 1986; the marked heterogeneity among studies; the relationship between the prevalence of front sleeping and year of recruitment and the size of the OR; and grouping of the comparator as non-front in some studies. Finally, many authors interpreted the front position as just one of a number of factors associated with SIDS and did not systematically review results from previous studies.12,57–59 The first overview of studies on the effect of sleeping position was published by Beal in 1988.60
It was striking that no studies were published on the effect of sleeping position between 1970 and 1986. Although several investigators collected data on sleeping position during the 1970s and early 1980s, their findings were not published until 1986 or later.33,58,59,61–65 Sleeping position may have been disregarded because the front position was not directly compared with the back, and the results of Frogatt and Carpenter were not combined. In addition, Frogatt66 questioned the validity of his results because they were only statistically significant when the usual sleeping position was compared, not if the position in which the SIDS victim was found was used. Bergman,67 may have further deterred research on sleeping position after finding that 85% of SIDS victims in a large US study were found on the front, and claiming, without reporting any control data, that this was similar to the community.
The lack of research attention on infant sleeping position between 1970 and 1986 contrasts with the increasing incidence of SIDS, and the steep increase in the proportion of infants sleeping front in several industrialized countries (Figures 3a, b, and c, and Figure 4).68–75 In the UK, the increase in SIDS incidence was attributed to diagnostic transfer—deaths previously classified as due to respiratory causes being classified as SIDS, which became a registrable cause only in 1971. However, there was concern that, while all other causes of infant deaths had declined during the 1970s and 1980s, SIDS and respiratory deaths combined had remained static.75,76 Clear evidence that SIDS incidence had truly increased and was not due to diagnostic transfer was not published until the 1990s (Figure 3c).68,69,74 In contrast, the decline in incidence following advice to avoid front sleeping in the ‘Back to Sleep’ campaigns (Figures 3a, b, and c) was rapid and undeniable, providing the strongest evidence to date for a harmful effect of the front position. SIDS incidence fell by 50–70% in numerous countries, in association with a fall in front sleeping. (Figures 3a, b, and c)75,77,78
A crude estimate of the number of babies who died in England and Wales owing to harmful health advice can be made by assuming that the rate of post neonatal SIDS would have remained at 0.6/1000 live births, the rate in the year after the government's ‘Back to Sleep’ campaign. From 1974, when SIDS was routinely used as a cause of death, until 1991, there were 11 000 excess deaths, or nearly 12 extra babies dying each week. However, the number of excess deaths is highest in the USA, where the prevalence of front sleeping was higher for longer than in any other country48,79(Figure 4). In the USA, rest of Europe, and Australasia, at least 50 000 excess deaths were attributable to harmful health advice.
We found substantial heterogeneity in the association between sleeping position and SIDS that was partly explained by the prevalence of the front (or side) position in control infants, and to a lesser extent, year of recruitment. In an era when front sleeping was the norm, parents who placed infants on the back were likely to have had socioeconomic characteristics that put them at high risk for SIDS, thereby diminishing the observed protective effect of the back position.80,81 Conversely, when prevailing advice was to avoid front sleeping, characteristics in those that did not take up this advice exaggerated the observed harmful effect of the front position. In other words, increased uptake of advice by families otherwise at low risk of SIDS produced a ‘healthy adopter’ effect that diminished evidence of harm. An alternative explanation is biased reporting of the position considered to be harmful by parents of SIDS victims. Another possibility is that studies showing an adverse effect of the sleeping position advocated at the time were less likely to be written about and published.
The effect of the era of health advice is best illustrated by comparing the pooled ORs for front vs back positions, before and after advice changed. For studies published between 196512 and 1995,37 the pooled OR was 2.95 (95% CI: 1.69–5.15, studies); thereafter the pooled OR was 6.91 (4.63–10.32). In the example of SIDS, a statistically significant association was still detectable because the OR was relatively large. However, these findings raise a general message for the evaluation of potentially harmful health advice that uptake by people at low risk of adverse outcomes could completely obscure evidence of harm.82
The fact that much heterogeneity between studies remained unexplained may be partly owing to difficulties in accurately measuring study characteristics. For example, we could not adequately measure the potential for reporting bias, which may have contributed to the relatively low OR for SIDS in three studies because staff responsible for recommending the front position also selected control babies and/or collected the data.61,64,65,83 A second factor in three studies, all conducted in the USA, may be the close matching of controls with cases based on age, hospital of birth, and ethnic group.37,40,84 If there had been uniform adoption of health advice within these communities, such close matching may have biased the association towards the null effect. In the first two of these studies, close matching, combined with the high prevalence of front sleeping, may have contributed to the relatively weak associations observed.37,84 Factors contributing to heterogeneity may also differ according to the era of health advice. This may partly explain differences between our results and a previous meta-analysis, restricted to studies published before 1990, that found that country of study, date of publication, matching, and position reported were associated with heterogeneity when sleeping front was compared with non-front.21
Conclusions
It is unusual for health advice to have such a profound effect on mortality and to detect such tragic effects from health advice that is not based on evidence of effectiveness. Had systematic reviews been common practice in the early 1970s, parents, professionals, and policy makers would have been aware of the cumulative effect of the front position on SIDS at least 15 years earlier than they were in 1988. Even if the results had been judged insufficient to change practice, they should have stimulated earlier publication of further studies.
Others have similarly highlighted the delayed introduction of effective treatment that could have been avoided if systematic review and meta-analysis had been used to summarize the accumulated evidence from randomized controlled trials.85,86 Interpretation of systematic reviews of observational studies is more difficult owing to the potential for bias and spurious precision.87,88 In particular, our results show that observational studies of health advice can be confounded by a ‘healthy adopter’ phenomenon that can diminish or obscure adverse effects of harmful health advice. All these problems are compounded when examining multiple risk factors. Nevertheless, when randomized controlled trials are lacking or not feasible, systematic review of observational studies is essential to guide policy and practice.
Conflict of interest
R.G. coordinated one of the included studies.34 None of the other authors have any conflict of interest.
Appendix: Hierarchical Bayesian model for case-control studies (front vs non-front)
. | Controls . | Cases . |
---|---|---|
Front | Fcont | Fcases |
Non-front | NFcont | NFcases |
ncont | ncases |
. | Controls . | Cases . |
---|---|---|
Front | Fcont | Fcases |
Non-front | NFcont | NFcases |
ncont | ncases |
. | Controls . | Cases . |
---|---|---|
Front | Fcont | Fcases |
Non-front | NFcont | NFcases |
ncont | ncases |
. | Controls . | Cases . |
---|---|---|
Front | Fcont | Fcases |
Non-front | NFcont | NFcases |
ncont | ncases |
Advice to put infants to sleep on the front for nearly a half century was contrary to evidence available from 1970 that this was likely to be harmful.
Systematic review of preventable risk factors for SIDS from 1970 would have led to earlier recognition of the risks of sleeping on the front and might have prevented over 10 000 infant deaths in the UK and at least 50 000 in Europe, the USA, and Australasia.
Attenuation of the observed harm with increased adoption of the front position probably reflects a ‘healthy adopter’ phenomenon in that families at low risk of SIDS were more likely to adhere to prevailing health advice.
We thank Iain Chalmers, Julian Higgins, and Jan van der Meulen for comments on an earlier draft of this article. Chris Hiley gave material from her PhD on the History of SIDS and Sima Patel acted as second reviewer for data extraction and helped with preliminary analyses. Bob Carpenter provided unpublished data for two of his studies. The Foundation for the Study of Infant Deaths allowed access to their archives. We thank the reviewers of an earlier version for their constructive comments, and Adèle Engelberts for providing incidence data for The Netherlands. All data are available on the web: http://www.ich.ucl.ac.uk/ich/html/academicunits/paed_epid/cebch/
References
Westcott WW. Inebriety in women and the overlaying of infants.
Abramson H. Accidental mechanical suffocation in infants.
Bowden KM. Sudden death or alleged accidental suffocation in babies.
New York State Department of Health. Merchanical suffocation: leading cause of accidental death in early infancy.
Woolley PV. Mechanical suffocation during infancy. A comment on its relation to the total problem of sudden death.
Werne J, Garrow I. Sudden deaths of infants allegedly due to merchanical suffocation.
Werne J, Garrow I. Sudden apparently unexplained death during infancy. I Pathologic findings in infants found dead.
Camps FE, Parish WE, Barrett AM, Coombs RRA, Gunther M. Hypersensitivity to milk and sudden death in infancy.
Strimer R, Adelson L, Oseasohn R. Epidemiologic features of 1,134 sudden, unexpected infant deaths. A study in the Greater Cleveland Area from 1956 to 1965.
Carpenter RG, Shaddick CW. Role of infection, suffocations and bottle-feeding in cot death: an analysis of some factors in the histories of 110 cases and their controls.
Hiley CMH. Back to Sleep: Cot death and Infant Care 1987–1994. Cambridge: University of Cambridge,
Greenland S, Rothman KJ. Measures of effect and measures of association. In: Rothman KJ, Greenland S (eds). Modern Epidemiology. Philadelphia: Lippincott-Raven,
Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses.
Egger M, Davey SG, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test.
Begg CB, Mazumdar M. Operating characteristics of a rank correlation test for publication bias.
Lau J, Antman EM, Jimenez-Silva J, Kupelnick B, Mosteller F, Chalmers TC. Cumulative meta-analysis of therapeutic trials for myocardial infarction.
Trikalinos TA, Churchill R, Ferri M et al. Effect sizes in cumulative meta-analyses of mental health randomized trials evolved over time.
Ioannidis JP, Contopoulos-Ioannidis DG, Lau J. Recursive cumulative meta-analysis: a diagnostic for the evolution of total randomized evidence from group and individual patient data.
Dwyer T, Couper D, Walter SD. Sources of heterogeneity in the meta-analysis of observational studies: the example of SIDS and sleeping position.
Sharp SJ, Thompson SG. Analysing the relationship between treatment effect and underlying risk in meta-analysis: comparison and development of approaches.
Thompson SG, Smith TC, Sharp SJ. Investigating underlying risk as a source of heterogeneity in meta-analysis.
Gordon M, Gordon R. A Baby in the House. A Guide to Practical Parenthood. London: Heinemann,
Fleming PJ, Gilbert R, Azaz Y et al. Interaction between bedding and sleeping position in the sudden infant death syndrome: a population based case–control study.
Ponsonby AL, Dwyer T, Gibbons LE, Cochrane JA, Wang YG. Factors potentiating the risk of sudden infant death syndrome associated with the prone position.
Markestad T, Skadberg B, Hordvik E, Morild I, Irgens LM. Sleeping position and sudden infant death syndrome (SIDS): effect of an intervention programme to avoid prone sleeping.
Klonoff-Cohen HS, Edelstein SL. A case–control study of routine and death scene sleep position and sudden infant death syndrome in Southern California.
Taylor JA, Krieger JW, Reay DT, Davis RL, Harruff R, Cheney LK. Prone sleep position and the sudden infant death syndrome in King County, Washington: a case–control study.
Fleming PJ, Blair PS, Bacon C et al. Environment of infants during sleep and risk of the sudden infant death syndrome: results of 1993–5 case–control study for confidential inquiry into stillbirths and deaths in infancy. Confidential Enquiry into Stillbirths and Deaths Regional Coordinators and Researchers.
Hauck FR, Moore CM, Herman SM et al. The contribution of prone sleeping position to the racial disparity in sudden infant death syndrome: the Chicago Infant Mortality Study.
Carpenter RG, Irgens LM, Blair PS et al. Sudden unexplained infant death in 20 regions in Europe: case control–study.
Brooke H, Gibson A, Tappin D, Brown H. Case–control study of sudden infant death syndrome in Scotland, 1992–5.
McGarvey C, McDonnell M, Chong A, O'Regan M, Matthews T. Factors relating to the infant's last sleep environment in sudden infant death syndrome in the Republic of Ireland.
Oyen N, Markestad T, Skaerven R et al. Combined effects of sleeping position and prenatal risk factors in sudden infant death syndrome: the Nordic Epidemiological SIDS Study.
Dwyer T, Ponsonby AL, Newman NM, Gibbons LE. Prospective cohort study of prone sleeping position and sudden infant death syndrome.
Dwyer T, Ponsonby AL, Couper D, Cochrane J. Short-term morbidity and infant mortality among infants who slept supine at 1 month of age—a follow-up report.
Brackbill Y, Douthitt TC, West H. Psychophysiologic effects in the neonate of prone versus supine placement.
Keitel HG, Cohn R, Harnish D. Diaper rash, self-inflicted excoriations, and crying in full-term newborn infants kept in the prone or supine position.
Hunt L, Fleming P, Golding J. Does the supine sleeping position have any adverse effects on the child? I. Health in the first six months. The ALSPAC Study Team.
Byard RW, Beal SM. Gastric aspiration and sleeping position in infancy and early childhood.
Dewey C, Fleming P, Golding J. Does the supine sleeping position have any adverse effects on the child? II. Development in the first 18 months.ALSPAC Study Team.
Davis BE, Moon RY, Sachs HC, Ottolini MC. Effects of sleep position on infant motor development.
Persing J, James H, Swanson J, Kattwinkel J. Prevention and management of positional skull deformities in infants. American Academy of Pediatrics Committee on Practice and Ambulatory Medicine, Section on Plastic Surgery and Section on Neurological Surgery.
Persson S, Ekbom A, Granath F, Nordenskjold A. Parallel incidences of sudden infant death syndrome and infantile hypertrophic pyloric stenosis: a common cause?
Galland BC, Taylor BJ, Bolton DP. Prone versus supine sleep position: a review of the physiological studies in SIDS research.
Froggatt P. Epidemiological aspects of the Northern Ireland study. In: Bergman AB, Beckwith JB, Ray CG (eds). Sudden Infant Death Syndrome. Proceedings of the Second International Conference on Causes of Sudden Death in Infants. Seattle: University of Washington Press,
McGlashan ND. Sudden infant deaths in Tasmania, 1980–1986: a seven year prospective study.
Cameron MH, Williams AL. Development and testing of scoring systems for predicting infants with high-risk of sudden infant death syndrome in Melbourne.
Beal SM. Sudden infant death syndrome: epidemiological comparisons between South Australia and communities with a different incidence.
de Jonge GA, Engelberts AC, Koomen-Liefting AJM, Kostense PJ. Cot death and prone sleeping position in The Netherlands.
Froggatt P, Lynas MA, MacKenzie G. Epidemiology of sudden unexpected death in infants (‘cot death’) in Northern Ireland.
Bergman AB, Ray CG, Pomeroy MA, Wahl PW, Beckwith JB. Studies of the sudden infant death syndrome in King County, Washington. 3. Epidemiology.
Engelberts AC, de Jonge GA, Kostense PJ. An analysis of trends in the incidence of sudden infant death in The Netherlands 1969–89.
Irgens LM, Markestad T, Baste V, Schreuder P, Skjaerven R, Oyen N. Sleeping position and sudden infant death syndrome in Norway 1967–91.
Hogberg U, Bergstrom E. Suffocated prone: the iatrogenic tragedy of SIDS.
Mitchell EA, Ford RP, Taylor BJ et al. Further evidence supporting a causal relationship between prone sleeping position and SIDS.
Taylor BJ. A review of epidemiological studies of sudden infant death syndrome in southern New Zealand.
Beal SM. Sudden infant death syndrome in South Australia 1968–97. Part I: changes over time.
Golding J, Limerick S, MacFarlane A. Variation of incidence with time, place, and age of infant. In: Golding J, Limerick S, MacFarlane A (eds). Sudden Infant Death: Patterns, Puzzles, and Problems. Shepton Mallet, UK: Open Books Publishing Ltd,
Willinger M, Hoffman HJ, Hartford RB. Infant sleep position and risk for sudden infant death syndrome: report of meeting held January 13 and 14, 1994, National Institutes of Health, Bethesda, MD.
McKee M, Fulop N, Bouvier P et al. Preventing sudden infant deaths—the slow diffusion of an idea.
Pollack HA, Frohna JG. Infant sleep placement after the back to sleep campaign.
Spencer N, Logan S. Sudden unexpected death in infancy and socioeconomic status: a systematic review.
Ponsonby AL, Dwyer T, Kasl SV, Couper D, Cochrane JA. Correlates of prone infant sleeping position by period of birth.
Ebrahim S, Smith GD. Health promotion for coronary heart disease: past, present and future.
Engelberts AC. Cot Death in The Netherlands: An Epidemiological Study. Amsterdam: VU University Press,
Hoffman HJ, Hillman LS. Epidemiology of the sudden infant death syndrome: maternal, neonatal, and postneonatal risk factors.
Antman EM, Lau J, Kupelnick B, Mosteller F, Chalmers TC. A comparison of results of meta-analyses of randomized control trials and recommendations of clinical experts. Treatments for myocardial infarction.
Egger M, Schneider M, Davey SG. Spurious precision? Meta-analysis of observational studies.
Ioannidis JP, Haidich AB, Pappa M et al. Comparison of evidence of treatment effects in randomized and nonrandomized studies.
Carpenter RG. Sudden and unexpected deaths in infancy (cot death). In: Camps FE, Carpenter RG (eds). Sudden and Unexpected Deaths in Infancy (Cot Death). Bristol. John Wright,
Wigfield RE, Fleming PJ, Berry PJ, Rudd PT, Golding J. Can the fall in Avon's sudden infant death rate be explained by changes in sleeping position?
Hiley CM, Morley CJ. Risk factors for sudden infant death syndrome: further change in 1992–3.
Willinger M, Hoffman HJ, Wu KT et al. Factors associated with the transition to nonprone sleep positions of infants in the United States: the National Infant Sleep Position Study.
Senecal J, Roussey M, Defawe G, Delahaye M, Piquemal B. Procubitus et mort subite inattendue du nourrison.
Beal SM, Finch CF. An overview of retrospective case-control studies investigating the relationship between prone sleeping position and SIDS.
Bouvier-Colle MH, Varnoux V, Hausherr E. Revue bibliographique des etudes sur la mort subite en relation avec la position de sommeil chez le nourrisson. Proceedings of Reunion du Groupe d'Etudes de Langue Francaise sur la mort subite du nourrisson. Nice. France.
Mitchell EA, Scragg R, Stewart AW et al. Results from the first year of the New Zealand cot death study.
Jorch G, Schmidt TS, Bajanowski T et al. Risk factors for sudden infant death (SID): epidemiologic study of two German districts 1990–1992 epidemiologische risikofaktoren des plotzlichen kindstods. Ergebnisse der westfalischen kindstodstudie 1990–1992.
Andersen M, Arnestad M, Rognum TO, Vege A. Krybbedod i ostlandsregionen 1984–92. En kartlegging av risikofaktorer. [Crib death in the eastern regions of Norway 1984–1992. A survey of risk factors].
Mitchell EA, Tuohy PG, Brunt JM et al. Risk factors for sudden infant death syndrome following the prevention campaign in New Zealand: a prospective study.
Schellscheidt J, Ott A, Jorch G. Epidemiological features of sudden infant death after a German intervention campaign in 1992.
Kleemann WJ, Schlaud M, Fieguth A, Hiller AS, Rothamel T, Troger HD. Body and head position, covering of the head by bedding and risk of sudden infant death (SID).
Skadberg BT, Morild I, Markestad T. Abandoning prone sleeping: effect on the risk of sudden infant death syndrome.
L'Hoir MP, Engelberts AC, van Well GT et al. Case-control study of current validity of previously described risk factors for SIDS in The Netherlands.
Mitchell EA, Thach BT, Thompson JM, Williams S. Changing infants' sleep position increases risk of sudden infant death syndrome. New Zealand Cot Death Study.
Dwyer T, Ponsonby AL, Gibbons LE, Newman NM. Prone sleeping position and SIDS: evidence from recent case-control and cohort studies in Tasmania.
Toro K, Sotonyi P. Distribution of prenatal and postnatal risk factors for sudden infant death in Budapest.
Saternus KS. Plötzlicher Kindstod-eine Folge der Bauchlage? Festschrift Professor Leithoff. Heidelberg: Kriminalistik Verlag,
Kahn A, Blum D, Hennart P et al. A critical comparison of the history of sudden-death infants and infants hospitalised for near-miss for SIDS.