What else do SIDS risk prediction scores predict?

Early Human Deuelopment, Elsevier

12 (1985) 247-260

247

EHD 00686

What else do SIDS risk prediction scores predict? Jean Golding Department

and Tim J. Peters

of Child Health, Utkersity Accepted

of Bristol, Bristol, U.K.

for publication

7 June 1985

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

scores;

sudden

infant

death syndrome

(SIDS);

social disruption

Introduction Independent evaluation [8] has confirmed the predictive power of two quite different risk scores for the sudden infant death syndrome (SIDS). By obtaining high-risk groups which included 20% of 16 771 infants in a national birth cohort, we identified 56% of 34 SIDS and 48% of 48 deaths from accidents or infections using the Sheffield, or Carpenter, score [3], while 68% and 46% respectively were identified using the ‘New’ score [6]. Although clearly over-represented in the high-risk category, these deaths still form a very small proportion of this group as a whole; the aim of the present study is to look at the children who, though scoring highly, survived. There are two reasons why it is important to assess the ways in which the high-scoring survivors differ from the rest of the cohort: first, the results may help shed light on the aetiology of SIDS itself; second, they should indicate whether in a follow-up study of these children it

Address for correspondence: Dr. Jean Gold&, Department Children. St. Michael’s Hill, Bristol, BS2 BBJ, U.K.

037%3782/85/$03.30

0 1985 Elsevier Science Publishers

of Child

Health,

B.V. (Biomedical

Royal

Diwsion)

Hospital

for Sick

248

would be feasible to attempt prevention than prevent the deaths themselves.

of specific conditions

in the survivors

rather

Materials and Methods Information was collected in structured questionnaires by the midwives who delivered the infants born in the United Kingdom during the week 5th to 11th April, 1970. This formed the British Births 1970 Survey, and included over 98% of eligible births [4,5]. For the present study, those items of information pertinent to the Carpenter score (mother’s age, number of previous pregnancies, duration of second stage of labour, mother’s blood group, birthweight of the infant, intention of the mother to breastfeed and whether a twin or singleton) were scored and summed for each infant according to the published schema [3]. The New score was computed by multiplying together the published score components [6]; these related to the social class of the husband, mother’s marital status, age and parity, interval from preceeding delivery to present conception, whether the mother knew the date of her last menstrual period, the amount she smoked during pregnancy, the sex, gestation and birthweight of the infant, whether a congenital defect was noted and whether the child was a twin or a singleton. Independent evaluation of these two risk prediction systems has been undertaken by comparing the distribution of scores in the total population of infants who survived the first seven days with those for the infants who subsequently died of (a) SIDS, and (b) potentially preventable conditions such as accidents, non-accidental injury and infections [8]. The present study reports on the analyses of data from the follow-up of the survivors of the birth cohort at five years of age [7]. Health visitors throughout the country were responsible for contacting the families and collecting detailed information on the child’s social, environmental and medical history. Each child was given a number of intellectual tests including the English Picture Vocabulary Test (EPVT) and the Copying Designs Test. Although the origninal birth study had included children born in Northern .Ireland, for political and technical reasons the children resident there at the age of five were omitted from the follow-up study. For each of the New and Carpenter scores in turn, the results presented here focus on the groups of children in either the 90th to 94th percentile range, or over the 94th percentile, of the scores in the birth survey. Neither distribution of scores was smooth; the New score selected the highest 9.3% of those children included at five, and the Carpenter score the highest 9.7%. Table I shows that 29.5% of all deaths aged 7 days to 5 years were in the high-risk category of the New score (3.579 or greater), as were 14.4% of the children lost to follow-up. In other words, compared with the overall response rate of 79.6% (12 743 out of 16 015 survivors), 80.5% of 14 362 low-risk children and 71.4% of 1653 high-risk children were followed up at five. This differential follow-up for the risk groups, while not insignificant, is unlikely to affect the results presented here. Similar figures were obtained when the Carpenter score was analysed in this way.

749

TABLE

I

Proportion of children in the New score categories or died between the ages of 7 days and 5 years

according

to whether

or not they were surveyed

New score

Surveyed at 5

Died 1 wk to 5 yr

Survived but not surveyed at 5

< 0.225 0.225-0.437 0.438-0.798 0.799-1.828 1 .X29%2.365 2.36663.578 3.579-6.103 > 6.103

20.9% 21.0% 20.0% 19.5% 4.6% 4.7% 4.4% 4.98

10.341 10.9% 19.9% 16.0% 7.1% 6.4% 10.9% 18.69

15.4% 17.0%, 18.9% 2184 5.9% 6.6% 6.8% 7.6%

n ==1009

12743

156

3 272

Children

not surveyed

because

resident

in Northern

Ireland

at ftve

have been excluded.

Another potential source of bias, for those children who were followed up, is that if the high scorers were more often well known to the health visitors than the low scorers, then there may have been a greater likelihood of childhood disorders and family problems being identified for these cases. In the event, however, there were no associations between the risk scores and how well the health visitor knew the family: for example, 8.7% of the 4106 children from families unknown to the health visitor scored highly on the New score, compared with 9.3% expected. The corresponding figures for the Carpenter score were 9.3% compared with 9.7% expected. The tables which follow show the proportion of children who scored highly on the risk prediction scores amongst those with a given problem ascertained at five. Using the standard chi-squared test for differences in proportions [l], these were compared with the expected values of, for example, 9.3% and 9.7% given from the total population. The continuity correction was applied.

Results Morbidity Table II gives the results for various signs and symptoms that had occurred during the first five years of life. There were no associations between high scores and a history of repeated sore throats requiring medical attention, hay fever/sneezing attacks or eczema. For the New score, there were statistically significant associations with a history of ear discharge (pus not wax). habitual snoring/mouth breathing. bronchitis, convulsions and a history of wheezing on the chest. though the magnitude of the increases in the proportion of affected children with high scores was very low (not more than 12.6% compared with 9.3% expected). The strongest association was between the children scoring highly on the New score and a history of pneumonia. It can be seen that this was especially true of the very high scorers (over

250 TABLE

II

Proportion symptoms

of children or diagnoses

(percent)

with high scores

among

those

reported

as ever having

had various

Proportion

with New score

Proportion

3.5796.103

6.104+

all 3.579 +

522542

543 +

all 522 +

Convulsions (n = 643) Pneumonia (n = 201) Bronchitis (n = 2107) Wheezing (n = 2624) Mouth breathing (n = 2453) Ear discharge (n = 1405) Frequent sore throats (n = 2542) Hay fever (n = 536) Eczema (n = 1495)

3.6 9.0 ** 5.6 ** 4.8 5.8 ** 5.6

9.0 16.4 6.1 6.8 6.1 6.1

12.6 25.4 12.3 11.6 11.9 11.7

4.8 8.0 * 5.6 5.3 4.2 5.1

7.6 ** 11.4 *** 6.3 ** 5.9 5.1 5.5

12.4 19.4 11.9 11.2 9.3 10.6

4.7 4.5 3.7

4.2 4.3 4.1

8.9 8.8 7.8

4.2 4.5 4.0

4.2 2.2 3.1

8.4 6.1 7.7

All children

4.4

4.9

9.3

4.6

5.1

9.7

Medical history (n = 100%)

( n = 12 743)

*** *** *** *** **

** *** *** *** *** **

with Carpenter

score

* *** *** **

* P < 0.05. ** P < 0.01. *** P i 0.001.

6.103). A similar general pattern was found for the Carpenter score, though for example the association with pneumonia was not quite as strong (Table II). From the data presented, it is clear that although high scores do predict slightly more children who have problems of the upper and lower respiratory tract, with the exception of pneumonia the associations are quite weak and prediction is not sufficiently accurate to warrant considering intervention.

Accidents There was a very slight association with high New scores for children who had three or more accidents; generally, however, the risk scores did not identify the five-year-olds reported by their mothers as having had accidents requiring medical advice or attention (Table III). In contrast, despite the small numbers, the scores were efficient at identifying children who had been suspected of being injured non-accidentally. Some 25.7% of children who were suspected by the health visitor, paediatrician or school of having been abused or being at risk of abuse (for example, there being a history of abuse of siblings) were in the top 9.3% of the New scores. Interpretation of these figures must recognise that, given a bruised child, the index of suspicion will be higher when the mother is known to be from a deprived social background. Hospital admissions Despite the fact that the incidence of most medical symptoms children with high scores (Table II), the risk of hospital admission

was not higher in was far greater in

251 ‘TABLE III Proportion of children (percent) with high scores among those who had experienced accidents medical attention, and among those suspected as being at risk of non-accidental injury (NAI) Nistorv of injury (n =lOO%)

Proportion

Accidents (No.) 1 +(n = 5539) 2+(n =1540) 3+(n = 439) Suspected of non-accidental injury ( r7= 70) All children

with New score 6.104+

3.579% 6.103

4.8 5.3 4.2

5.5 5.8 6.2

11.4 **

(n = 12 743)

14.3 ***

4.4

Proportion

all 3.579 +

522542

10.3 11.1 12.4

25.7 ***

4.3

4.9

9.3

requiring

with Carpenter

score

543+

all 522t

4.9

5.7

5.6

5.7

5.7

5.0

10.6 11.3 10.7

18.6 ***

4.6

22.9 ***

5.1

9.1

* P < 0.05. ** Pi 0.01. *** P < 0.001

T.4BLE

IV

Proportion

of children

(percent)

History of hospital admissions (n = 100%)

Hospital 1 +(n 2+(n 4+(n total 1 + HA 1 t- HA 2 +- HA 1 + HA 1 i- HA 2 + HA I+ HA 1 + HA

admissions = 3251) = 894) =115) 15 nights + (n = 681) for accidents (n = 806) for convulsions (n = 293) for convulsions (n = 55) for asthma (n = 72) for resp. infect. (n = 424) for resp. infect. (n = 67) for operations (n = 1273) for ENT (n = 520)

All children ENT = *P i ** P i *** Pi

(n = 12 743)

conditions 0.05. 0.01. 0.007.

with high scores among

those with histories

of hospital

admission

(HA)

Proportion

with New score

Proportion

with Carpenter

3.5796.103

6.104+

al1 3.579 +

522542

543 +

all 522 +

6.2 7.0 9.6 10.3 6.0 4.4 7.3 8.3 8.5 13.4 5.7 5.0

8.6 72.0 13.0 15.9 9.3 8.9 12.7 5.6 14.2 17.9 6.8 4.6

14.8 19.0 22.6 26.2 15.3 13.3 20.0 13.9 22.1 31.3 12.5 9.6

5.8 6.7 11.3 7.8 6.6 3.8 3.6 12.5 6.6 11.9 4.9 4.4

7.7 9.6 9.6 13.4 8.3 8.5 7.3 5.6 12.7 11.9 6.3 4.2

13.5 16.3 20.9 21.2 14.9 12.3 10.9 18.1 19.3 23.8 11.2 8.6

*** *** * *+*

*** ***

4.4

of ear, nose and throat.

4.9

*** *** *** *** *** ** * *** ***

9.3

*** *** *** *I* *** * * *** *** ***

4.6

*** ** ** *** *

** **

5.1

*** **I *** *** *

+** * *

9.7

score

*** *** *** *** ***

* *** ***

252 TABLE

V

Proportion problems Sensory problem

of children

(percent)

with high scores among those with a history

(n = 100%)

Squint (n = 930) Vision problem (not squint) (n = 430) Suspected hearing problem (n =1018) (n = 766) History of stammer/stutter History of other speech problem (n =1322) All children

(n = 12 743)

of vision, hearing

Proportion

with New score

3.5796.103

6.104 +

all 3.579 +

522542

543 +

all 522 +

1.3 **+

7.3 ***

14.6 ***

5.3

6.8 *

12.1 *

4.9

7.0

11.9

3.7

4.2

7.9

4.6 5.9

4.6 6.9 **

9.2 12.8 ***

5.4 5.3

4.1 5.1

9.5 11.0

5.3

6.5 **

11.8 ***

5.9 *

6.1

12.0 **

4.4

4.9

4.6

5.1

9.3

Proportion

and speech

with Carpenter

score

9.7

* P i 0.05. ** P < 0.01. *** P < 0.001.

this group (Table IV). Using either the New score or the Carpenter score, the high-risk group were more likely to be admitted to hospital, more likely to have multiple admissions, and more likely to have a total duration of stay in excess of two weeks. Among specific reasons for admission, those for respiratory infection were the best predicted. This result was equally true of children with and without a history of pneumonia. Interestingly, though, there was no relationship between the high risk scores and hospital admission for ear, nose and throat conditions, and little evidence of an association with admission for asthma. Many factors influence the decision as to whether or not a child should be admitted for a given condition. One aspect will be the doctor’s assessment of how well the family could cope if the child were to be nursed at home, another will be his assessment of the seriousness of the condition. Thirdly, especially when it comes to planned admissions for surgery, it is often the well-educated, middle-class mother who is likely to insist that her child be admitted. It seems likely that the first of these factors is the predominant one in explaining the findings in Table IV. Speech,

vision and hearing problems

The SIDS scores were marginally efficient at identifying children with a history of stammer/stutter or other speech problems (Table V), but the history of squint was the problem that was best predicted, especially by the New score. There were no associations with suspected hearing problems or vision problems other than squint. Behaviour

of the children

There was no association between high scores for SIDS and the mother’s report of whether the child had been a problem as a baby (Table VI). In particular, there were

253 TABLE

VI

Proportion

of children

(percent)

Behaviour problem (n = 100%)

Proportion

Behaviour as a baby excessive crying (n = 1781) feeding difficulties (n =1673) sleeping problems (n =I 717) Behaviour at five wets bed 1+ /wk (n = 1383) temper tantrums 1 +/wk (n=1541) highest quartile on Rutter score (n = 2271) attended Child Guidance Clinic (n = 84) All children

with high scores among

(n = 12743)

those with various

with New score

behaviour

problems

Proportion

with Carpenter

522542

543 +

score

3.5796.103

6.104+

4.0

5.2

9.2

4.3

4.8

9.1

4.5

5.7

10.2

4.5

5.9

10.4

3.8

4.1

7.9

4.3

4.3

8.6

all 3.579 f

all 522i

6.5 ***

10.0 ***

16.5 ***

6.6 ***

8.1 ***

14.7 ***

6.2 ***

1.6 ***

13.8 ***

6.0 *

7.6 ***

13.6 ***

6.8 ***

8.0 ***

14.8 ***

5.8 *

7.4 *

13.2 ***

7.1

4.8

11.9

6.0

4.8

10.8

4.4

4.9

9.3

4.6

5.1

9.7

* P < 0.05. ** P i 0.01. *** Pi 0.001

no associations with excessive crying, feeding problems or sleeping problems. Concerning behaviour at five, children who had high scores were more likely to be wetting their beds at least once a week and to have temper tantrums at least once a

TABLE

VII

Proportion

of children

(percent)

Intellectual ability (n = 100%:)

Scored < 1 S.D. below mean on EPVT (n = 1934) Scored 0 or 1 on Copying Designs Test (n = 441) Considered intellectually backward/abnormal by health visitor (n = 662) All children

(n = 12 743)

* P < 0.05. ** P < 0.01. ***p < 0.001.

with high scores among those with poor performance

on intellectual

tests

Proportion

with New score

Proportion

with Carpenter

3.5796.103

6.104+

all 3.579+

522542

543 +

all 522 +

8.1 ***

10.3 ***

18.4 ***

7.4 ***

10.3 ***

17.7 ***

10.4 ***

13.2 ***

23.6 ***

10.0 ***

10.4 ***

20.4 ***

10.3 ***

11.5 ***

21.8 ***

9.1 ***

9.7 ***

18.8 ***

4.6

5.1

4.4

4.9

9.3

score

9.7

254 TABLE

VIII

Proportion

of children

(percent)

with high scores among those said to have various categories

Presence of disability (n = 100%)

Proportion 3.5196.103

6.104 +

No, none (n = 11270) Yes, but not a handicap (n = 376)

4.2

4.8

of disability

Proportion

with Carpenter

522542

543 +

9.0

4.4

4.9

9.3

with New score all 3.579 +

score

all 522 +

5.9

6.9

12.8 *

5.3

6.1

11.4

Yes, mild handicap (n = 330)

6.1

9.7 ***

15.8 ***

8.5 **

9.1 ***

17.6 ***

Yes, severe handicap (n=99)

9.1 *

19.2 **

9.1 *

6.1

15.2

All children

4.4

4.6

5.1

9.1

(n = 12743)

10.1 * 4.9

9.3

* P < 0.05. ** P < 0.01. *** P < 0.001

week. An indication of the number of specific behaviour problems that a child might have is given by the Rutter score: Table VI shows that the children with high Rutter scores were somewhat more likely to have high SIDS risk scores. There was, however, no significant association between high SIDS scores and whether the child had attended a Child Guidance Clinic, though the numbers involved are quite small. Intellectual

development

Poor intellectual development was predicted far more accurately by high SIDS scores than were behaviour problems; over one-fifth of children who were considered to be intellectually backward or abnormal by the health visitor were in the top 9% of New scores (Table VII). For a more objective test of intellectual development, the Copying Designs Test, nearly a quarter of the children who were virtually unable to copy designs were to be found in this high-risk group. A similar, though slightly weaker, association was found with poor scorers on the English Picture Vocabulary Test (EPVT). Handicap/disability

The health visitor was asked from her own knowledge and observations, and from available records, to assess whether the child had any mental or physical disability or handicap, or any other condition interfering with normal everyday life or which might be a problem at school. The results in Table VIII show that high scores did predict the children with disabilities, especially those who were considered to have a handicap which would interfere with school life. Health behaviour

There were very strong associations for parental health behaviour on behalf of the child (Table IX). For example, the highest 9.3% of the New scores included almost

25s TABLE

IX

Proportion behaviour

(percent) indices

of high scores among children

Proportion

Health hehaviour

(n = 100%) Failed to have child immunised at all (n = 329) Only 1 or 2 attendances for immunisation (n = 641) Failed to take child to the dentist (n = 3061) Maternal Malaise score IO + (n =1229) All children

(n = 12 743)

whose parents

with New score

were reported

as having adverse

health

Proportion

with Carpenter

3.5796.103

6.104+

all 3.579 +

5222 542

543 +

all 522 +

8.2 ***

14.6 ***

22.8 ***

13.1 ***

14.9 ***

28.0 ***

8.6 ***

12.3 ***

20.9 ***

7.5 ***

11.4 ***

18.9 ***

7.0 ***

8.2 ***

15.2 ***

6.9 ***

7.9 ***

14.8 ***

8.2 ***

9.8 ***

18.0 ***

5.1

9.3 ***

14.4 ***

4.4

4.9

4.6

5.1

9.3

score

9.7

* P i 0.05. ** P i 0.01. *** P < 0.001.

23% of parents who failed to have any immunisation at all carried out on their children, and just under 21% of parents who failed to have a complete course of immunisations carried out. Though less strongly, failure to take the child to the dentist was also predicted by both the high New and Carpenter scores. In Table IX is also included an assessment of the mother’s mental and physical well-being, the ‘Malaise score’, obtained by asking the mother a series of yes/no questions concerning various signs and symptoms such as headaches, depression and inability to get to sleep. Scores ranged from 0 to a maximum of 21, and mothers scoring over 10 were predicted fairly well by the SIDS scoring systems. Whether this means that these mothers were under more stress, or whether their subjective expectation of life was different from those with other scores, must remain a question for further research.

Social change

In Table X are shown the various social changes that had occurred to the child in the period from birth to the age of five. It can be seen that the prediction for a majority of these events is far more precise than that obtained for any of the health or behaviour indices. The most accurate predictions were for being taken into care and losing the natural mother under various circumstances: living with a mother substitute or living alone with the father by the age of five were very well predicted. Similarly, there were strong associations with the loss of the natural father. In addition, the children with high scores were more likely to have moved house frequently. Since the New score took into account the marital status of the mother at the birth of the child, the analyses for social change were repeated including only

256 TABLE

X

Proportion

of children

(percent)

with high scores among those to whom various Proportion with New score

Social events (n =lOO%)

social events had occurred

Proportion Carpenter

with score

3.5196.103

6.104 +

all 3.519 +

522542

543 +

all 522+

Living alone with father at 5 (n = 51)

11.8 *

21.6 ***

33.3 ***

7.8

15.7 **

23.5 **

Living alone with mother (n = 630)

10.8 ***

14.6 ***

25.4 ***

7.3 **

8.7 ***

16.0 ***

Living with mother (n =172)

at 5

substitute 18.0 ***

23.3 ***

41.3 ***

9.3 **

15.7 ***

25.0 ***

Living with father substitute (n = 502) Child ever taken into care (n = 177)

13.8 *** 18.6 ***

19.1 *** 26.6 ***

32.9 *** 45.2 ***

9.0 *** 8.4

10.6 *** 17.4 ***

19.6 *** 25.8 ***

Frequent household (n =147)

12.2 ***

15.6 ***

27.8 ***

4.1

12.2 ***

16.3 ***

All children

moves (6 +)

( n = 12 743)

4.4

4.9

9.3

4.6

5.1

9.7

* P <: 0.05. ** P < 0.01. *** P c: 0.001.

TABLE

XI

Proportion of children (percent) with high New scores among those to whom various occurred (children whose parents were married at the time of delivery only) Social events (n =lOO%)

Proportion

Living alone with father at5(n=47) Living alone with mother at5(n=443) Living with mother substitute (n = 78) Living with father substitute (n = 268) Child ever taken into care (n = 90) Frequent household moves (6 + ) (n = 123) All children

( n = 12 037)

- * P i 0.05. ** P i 0.01. *‘l* P < 0.001.

social events had

with New score

3.5796.103

6.104+

all 3.579 +

10.6 *

21.3 ***

31.9 ***

5.4 *

9.5 ***

14.9 ***

12.8 ***

14.1 ***

26.9 ***

9.7 ***

10.1 ***

19.8 ***

12.2 ***

20.0 ***

32.2 ***

7.3 *

14.6 ***

21.9 ***

3.5

3.6

7.1

25? TABLE

XII

Proportion five

of children

(percent)

Social circumstances ( n = 100%)

with high scores among

Proportion 3.5796.103

those living in various

with New score

Proportion

6.104+

all 3.579 +

522542

adverse

circumstances

with Carpenter 543 +

at

score

all 522-k

-Resident in poor urban area

(I* = 1003) Persons per room

7.7 ***

10.4 ***

18.1 ***

8.6 ***

9.7 ***

18.3 ***

>lSO(n=2246) Standard of furniture/ equipment:

7.5 ***

10.0 ***

17.5 ***

8.0 ***

11.5 ***

19.5 ***

low/very low (n = 553) Tidiness of household:

13.0 ***

19.3 ***

32.3 ***

12.7 ***

15.6 ***

28.3 ***

untidy/chaotic (n = 846) Relationship with neighbours:

10.3 ***

12.8 ***

23.1 ***

8.3 ***

12.5 ***

20.8 ***

don’t mix (n = 535) on bad terms (n = 72)

6.9 ** 19.4 ***

12.5 *** 11.1 *

19.4 *** 30.5 ***

8.0 *** 12.5 **

9.7 *** 19.4 ***

17.7 *** 31.9 ***

All children (n = 12 743) _ * P < 0.05. ** P < 0.01. *I* P < 0.001.

4.4

4.9

9.3

4.6

5.1

9.7

mothers who had been married at the time of delivery (Table XI). The major associations were all still present: high SIDS risk scores predicted marital change and children being taken into care.

Environment at five Children with high scores were more likely to live in poor urban areas and overcrowded accommodation than those with low scores (Table XII). More accurately predicted, however, was the standard of furniture and equipment in the household: among the children whose health visitors regarded the standard of furniture or equipment as low or very low, one-third were found in the high New score group. The health visitor was also asked to assess whether the house was in a tidy or untidy state, regardless of the standard of equipment. Among the group where the health visitor had considered the house as being untidy or even chaotic, nearly a quarter of the mothers were in the high New score group. There was also an association between high SIDS scores and the relationship between the family and their neighbours. Children whose parents did not mix with their neighbours were more likely to have high risk scores, but the association was especially strong for the small group who declared that they were on bad terms with their neighbours.

258

Discussion

Given the differences in their composition, the performances of the New score and the Carpenter score in terms of risk prediction have been remarkably similar throughout these analyses, although overall the New score has been slightly more efficient than the Carpenter score. For both scores there was generally a trend in that the very highest scores were better predictors than the moderately high. For the sake of clarity, however, we refer in what follows to the New score alone. An analysis based on the differences between groups of children must, perforce, lose the fine detail in the generalisations. It is therefore important to point out that the very high risk group (those infants with scores of 6.104 or more) contains a mixture as diverse as the three children described below. Child A

At the age of five was living with his natural mother and three siblings. His mother had divorced his natural father when he was 2 months old; his present step-father was in prison. The home was untidy and the furniture and equipment was of a low standard. The mother had been in contact with the probation service and the social services. Her ‘Malaise’ score was 10. The child had been admitted to hospital once, for a febrile convulsion, and at the age of five was considered by the health visitor to be intellectually “definitely backward”. Child B

The parents had separated by the time the child was five. There had been five household moves and the child had, in addition, been taken into care on three occasions (two of these were due to the mother’s psychiatric admission and one for social problems). She had been admitted to hospital twice, once for swallowing her mother’s LSD, once for a chest infection. She was considered to be at risk of non-accidental injury. Child C

Lives with both natural parents, his co-twin and two siblings. He weighed only 1950 g when born, after 34 weeks gestation. Nevertheless he has thrived and has no problems. He has received a full course of immunisations and was described by the health visitor as a happy, well-adjusted child. Notwithstanding these individual variations, in order to make any inferences from the results it is necessary to return to the epidemiological method and consider average measures for groups of children. One example of a summary statistic to represent the magnitude of an association between a problem or condition for the child and a SIDS prediction score is the relative risk. This is defined here as the ratio of the proportion of high scores (3.579 + for the New score) among those with the condition, to the proportion of high scores among all children included in the follow-up (or all first week survivors for the mortality outcomes). In Table XIII are listed those relative risks which were over 2.00 and significantly associated with the

259 TABLE

XIII

Relative

risk of the child having a given condition

Kelative risk *

Condition’

4.86 4.44 3.58 3.54 3.41 3.37 3.28 2.82 2.78 2.73 2 73 2.54 2.48 2.45 2.44 2.43 2.34 2.25 2.09 2.04 2.03

Taken into care Living with mother substitute Living alone with father, no mother figure Living with father substitute Low standard of furniture/equipment 2 + HA for respiratory infection On bad terms with neighbours At least 15 nights in hospital Suspected non-accidental injury Living with mother, no father figure History of pneumonia Poor at copying designs House is untidy Child not immunised at all 1 + HA for respiratory infection 4 + hospital admissions Child intellectually abnormal Failure to have full course of immunisations Mother ‘does not mix’ with neighbours 2 + hospital admissions 6 + household moves

For reference 4.20 2.‘78

SIDS Deaths from accident

if he/she

or infection

scores 3.579 or more on the New score

(801 (711 (171 (1651 (1781 (211 (221 (1781 (181 (1601 (511 (1041 (1951 (751 (961 (261 (1441 (1341 (1041 (1701 (411

(151 (141

“Given relative to the total population and listed in rank order: risks under 2.00 or not significant 1% level have been omitted. h Number of high scorers with the condition given in parentheses

at the

top decile of the New score. It can be seen that the largest relative risks were for the social events in childhood and the social conditions in which the child was living at five. Specifically, the highest risks were for the child being taken into care, living without its natural mother and living without its natural father. The housing conditions of these children were equally cause for concern, but this was not merely due to the quality of the homes as there was also a significant association with being on bad terms with one’s neighbours. There were strong associations with a history of pneumonia and hospitalisation for respiratory infection; a propensity for chest infections may well be of importance in the aetiology of SIDS. We emphasise, however, that the relationships between the characteristics of the survivors and their risk scores for SIDS only represents an indirect investigation of the associations with SIDS itself. The present analyses can therefore only tentatively suggest possible aetiological factors. Hospital admissions for other reasons were less likely to be associated with high scores since there were no differences in the prevalences of the conditions themselves across the risk groups.

260

Nevertheless, there was a significant association with hospitalisation for accidental injury, even though the children themselves were no more likely to have had accidents than their low-scoring peers. It therefore seems likely that this association with hospitalisation is a reflection of the reaction of the medical profession to the home circumstances of the child. It must be stressed that although relative risks of social events are very high in the group of children at high risk of SIDS, the majority of families in this group are stable, they live in tidy homes and are on good terms with their neighbours. Nonetheless, a lack of ability to relate to their spouses and children may well be associated with some cases of SIDS. In such an instance, one would postulate that parental sensitivity to the needs of a mildly ill child may be lacking and the appropriate action not taken. One of the most striking associations in the Sheffield intervention study [2] was that between refusal to participate and the subsequent death of the child.

Acknowledgements We are grateful to the many health visitors who collected the data for the follow-up study and to the members of the District and Area Health Authorities who enabled the survey to take place. The British Births Survey was sponsored jointly by the National Birthday Trust Fund and the Royal College of Obstetricians and Gynaecologists, and the data was collected by midwives. Jean Golding is a Wellcome Trust Senior Lecturer and at the time of the analyses for this paper Tim Peters was funded by a Birthright research grant. We also thank Richard Bernard and Peter Thomas for computing assistance, and Carroll Baker for typing the manuscript.

References 1 Armitage, P. (1971): Statistical Methods in Medical Research. Blackwell Scientific Publications, Oxford. 2 Carpenter, R.G. and Emery, J.L. (1977): Final results of study of infants at risk of sudden death. Nature, 268, 124-725. 3 Carpenter, R.G., Gardner, A., McWeeny, P.M. and Emery, J.L. (1977): Multistage scoring system for identifying infants at risk of unexpected death. Arch. Dis. Child., 52, 606-612. 4 Chamberlain, G., Philipp, E., Howlett, B. and Masters, K. (1978): British Births 1970, Vol. 2, Obstetric Care. William Heinemann Medical Books, London. 5 Chamberlain, R., Chamberlain, G., Howlett, B. and Claireaux, A. (1975): British Births 1970, Vol. 1, The First Week of Life. William Heinemann Medical Books, London. 6 Gelding, J., Limerick, S. and Macfarlane, J.A. (1985): Sudden Infant Death: Patterns, Puzzles and Problems. Open Books, London. 7 Osborn. A.F., Butler, N.R. and Morris, A.C. (1984): The Social Life of Britain’s Five-Year-Olds. Routledge and Kegan Paul, London. 8 Peters, T.J. and Golding, J. (1985): Prediction of sudden infant death syndrome: an independent evaluation of four scoring methods. Statistics Med., in press.