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• Re: Consider absolute risks in SIDS prevention
  Peter Blair
  Published on: 7 July 2000
• Consider absolute risks in SIDS prevention
  Stuart Logan
  Published on: 26 June 2000

• Published on: 7 July 2000

  Re: Consider absolute risks in SIDS prevention

  • Peter Blair, medical statistician

  Authors response

  Poor postnatal weight gain was a significant factor in the multivariate analysis despite controlling for low birthweight, prematurity, neonatal problems, poor socio-economic status and many other potential confounding factors and remained significant when further highly predictive covariates of SIDS such as infants put down prone, infants found with head covered and tobacco exposure were added...

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  Authors response

  Poor postnatal weight gain was a significant factor in the multivariate analysis despite controlling for low birthweight, prematurity, neonatal problems, poor socio-economic status and many other potential confounding factors and remained significant when further highly predictive covariates of SIDS such as infants put down prone, infants found with head covered and tobacco exposure were added to the model. In this sense postnatal weight gain was independently associated with an increased risk of SIDS. We also found the difference in weight gain between the two groups measured from birthweight to the last known weight was equally apparent if measured from birth to the 6 week assessment. We therefore stand by our conclusion in the abstract that poor postnatal weight gain ‘was independently associated with an increased risk of SIDS’ and also that poor postnatal weight gain ‘could be identified at the routine six week assessment’.

  We find it difficult to understand how this conclusion advocates an intervention campaign on the basis of these two statements and disagree with Logan and colleagues that our discussion on this matter was circumspect. We point out clearly that poor weight gain itself is not a sensitive marker and that it ‘should be seen as a thread in a web of factors that render an infant vulnerable to SIDS and is both a consequence of adverse health and social conditions’.

  We agree that absolute risks must be used for targeted prevention campaigns but do not advocate such a campaign based on our solitary finding. Preliminary analysis of risk scoring on the first two years of our dataset, tested on the third year show that 42% of SIDS families can be identified from 8% of the population using just a few prenatal factors. Incorporating postnatal factors such as weight gain may improve the specificity and sensitivity of such a scoring system.

  To our knowledge the “Back to Sleep” campaign initiated in October 1991 has not been evaluated in an appropriately controlled study yet the SIDS rate in England & Wales more than halved from 1.7 deaths per 1000 livebirths in 1990 to 0.77 deaths in 1992.[1] Findings from our study have helped build upon the advice regarding safe sleeping practices, parents are now advised not only to avoid placing infants in the prone position but also the side position, bed-sharing under certain circumstances, sharing a sofa to sleep and to avoid head covering by placing the feet of the infant at the foot of the cot. In 1998 the SIDS rate fell a further 25% in England & Wales to 0.45 deaths per 1000 livebirths.[2] There is no direct evidence that these recommendations and fall in SIDS rates are linked although the dramatic fall in the prevalence of parents placing their infant in the prone position to sleep (57% before the campaign[3] to 3% after the campaign[4]) suggest many parents take up such recommendations.

  A targeted population intervention would perhaps be inappropriate given the reduced number of SIDS deaths in this country but risk scoring systems could be used to identify and study ‘high risk’ families to both increase our understanding of the risks associated with the infant sleeping environment and improve the advice we give parents in the hope that the number of SIDS deaths reduces still further.

  Peter S Blair*
  Peter J Fleming*
  Martin Ward Platt#

  *FSID Research Unit, Dept Child Health,
  Royal Hospital for Children, St Michael’s Hill,
  Bristol BS2 8BJ, UK

  # Newcastle Neonatal Service, Ward 35,
  Royal Victoria Infirmary, Newcastle upon Tyne NE1 4LP, UK

  1. OPCS Monitor. Sudden infant deaths, 1990-94. DH3 95/3. Crown copyright 1995:4.

  2. ONS Health Statistics Quarterly 05 Spring 2000. The Stationery Office: 10.

  3. 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. BMJ 1990;301:85-9.

  4. Fleming PJ, Blair PS, Bacon C et al. Environment of infants during sleep and risk of the sudden infant death syndrome: results from 1993-5 case-control study for confidential inquiry into stillbirths and deaths in infancy BMJ 1996;313:191-5.

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  Conflict of Interest:
  None declared.

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• Published on: 26 June 2000

  Consider absolute risks in SIDS prevention

  • Stuart Logan, Paediatric Epidemiologist, Epidemiologist, Consultant Paediatrician respectively
  • Other Contributors:
    • "Helen Bedford, David Elliman"

  Sir

  The demonstration by Blair et al[1] of an association between poor postnatal growth and an increased risk of SIDS, is a useful addition to our understanding of the aetiology of this condition. It is unfortunate that the conclusion in the abstract that "Poor postnatal weight gain was independently associated with an increased risk of SIDS and could be identified at the routine six week assessment" (italics added...

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  Sir

  The demonstration by Blair et al[1] of an association between poor postnatal growth and an increased risk of SIDS, is a useful addition to our understanding of the aetiology of this condition. It is unfortunate that the conclusion in the abstract that "Poor postnatal weight gain was independently associated with an increased risk of SIDS and could be identified at the routine six week assessment" (italics added) goes beyond the data presented.

  It can be estimated from the data in this study that the overall risk of SIDS was 0.77/1000 livebirths. The risk in babies with birthweights >15th centile, the group in whom the relationship with postnatal growth was detected, was 0.68/1000. Given the reported odds ratio of 1.75 associated with being in the slowest growing 16% who might be identified at by six weeks, the data suggest that the absolute risk of SIDS among this group would be about 1.1/1000. Even a programme targeted at infants below the 2nd centile for growth at six weeks, would identify a group whose absolute risk of SIDS was about 4.2/1000, i.e. for every infant who might benefit from the intervention, there would be 240 who wouldn't. Even if it were accepted that this level of risk was sufficient to trigger an intervention, the nature of the intervention remains unclear.

  To the best of our knowledge, with the exception of the 'Back to Sleep' campaign, there is no convincing evidence of the effectiveness of any intervention aimed at preventing SIDS. None of the intervention programmes described in the accompanying commentary[2] have been evaluated in appropriately controlled studies.

  The discussion in the paper is rather more circumspect than the conclusion in the abstract, but it is the latter which, reinforced by the accompanying commentary, is likely to have disproportionate impact on those readers who do not read the whole paper. In the commentary Dr Carpenter acknowledges that the low rates of SIDS make such interventions difficult to justify but then suggests that "Targeting such infants for weight monitoring at home….. will also identify numerous other problems at a remedial stage." This is a suggestion for which there is currently little evidence.

  There are clear dangers in recommending population interventions on the basis of relative risks without taking account of absolute risks or of the need for interventions to be of proven effectiveness.

  Stuart Logan*
  Helen Bedford*
  David Elliman#

  *Department of Paediatric Epidemiology,
  Institute of Child Health,
  30 Guilford Street, London WC1N 1EH, UK

  #St Georges Hospital,
  Blackshaw Road, London SW17 0QT, UK

  References

  1. Blair PS, Nadin P, Cole TJ, Fleming PJ, Smith IJ, Platt MW, Berry PJ, Golding J. Weight gain and the sudden infant death syndrome: change in weight z scores may identify infants at increased risk. Arch Dis Child 2000;82:462-9.

  2. Carpenter RG [Commentary]. Arch Dis Child 2000;82:469.

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  Conflict of Interest:
  None declared.

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