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Risk and preventive factors for cot death in The Netherlands, a low-incidence country

Article (PDF Available) inEuropean Journal of Pediatrics 157(8):681-8 · September 1998with38 Reads
DOI: 10.1007/s004310050911 · Source: PubMed
Monique Lhoir at Wageningen University & Research
  • 29.82
  • Wageningen University & Research
Adele C Engelberts at Orbis Medisch Centrum
  • 30.45
  • Orbis Medisch Centrum
Gijs van Well at Maastricht Universitair Medisch Centrum
  • 29.24
  • Maastricht Universitair Medisch Centrum
Abstract
In the Netherlands an 18 months case control study into cot death was under-taken as part of the European Concerted Action (ECAS) on sudden infant death syndrome to determine the relative risk of prone sleeping and other sleep practices. Physicians in the Netherlands were asked to report to the study centre all sudden and unexpected deaths of children between 1 week and 2 years of age. Non cot death cases were deleted from further analysis after a consensus was reached by three pathologists, not primarily involved in the post mortem diagnosis. A positive response of families was achieved in 91% of cases registered in the Central Bureau of Statistics. The study comprised 73 cot deaths and 146 controls, two for each case and matched for date of birth. All families were visited at home for completion of a questionnaire. The cot death rate has dropped considerably over the past 10 years after the recommendations on supine sleeping to a low of 0.26 per 1000 live born infants. In addition to the ECAS objective, we wanted to establish whether previously found risk factors are still valid in the present situation or that new factors might have emerged, some of them possibly protective. Conclusion Placing an infant prone or on side on last occasion, secondary prone position (not placed prone but turned to prone), inexperienced prone sleeping and use of a duvet, leading to head and body being covered, were shown to be risk factors. Preventive factors were using a cotton sleeping-sack and a dummy. Even in a low incidence country, such as the Netherlands, there are indications that further prevention is possible.
Figures
Fig. 1 Dutch sleeping-sack (`trappelzak'), left : quilted sleeping-sack, right : plain cotton sleeping-sack 
Dutch sleeping-sack (`trappelzak'), left : quilted sleeping-sack, right : plain cotton sleeping-sack
PREVENTIVE PEDIATRICS AND EPIDETIOLOGY
M. P. L'Hoir á A. C. Engelberts á G. Th. J. van Well á S. McClelland á P. Westers
T. Dandachli á G. J. Mellenbergh á W. H. G. Wolters á J. Huber
Risk and preventive factors for cot death
in The Netherlands, a low-incidence country
Received: 16 July 1997 / Accepted 12 revised form: 8 December 1997
Abstract In the Netherlands an 18 months case control study into cot death was under-
taken as part of the European Concerted Action (ECAS) on sudden infant death
syndrome to determine the relative risk of prone sleepi ng and other sleep practices.
Physicians in the Netherlands were asked to report to the study centre all sudden and
unexpected deaths of children between 1 wee k and 2 years of age. Non cot death cases
were deleted from further analysis after a consensus was reached by three pathologists,
not primarily involved in the post mortem diagnosis. A positive response of families was
achieved in 91% of cases registered in the Central Bureau of Statistics. The study com-
prised 73 cot deaths and 146 controls, two for each case and matched for date of birth. All
families were visited at home for completion of a questionnaire. The cot death rate has
dropped considerably over the past 10 years after the recommendations on supine
sleeping to a low of 0.26 per 1000 live born infants. In addition to the ECAS objective, we
wanted to establish whether previously found risk factors are still valid in the prese nt
situation or that new factors might have emerged, some of them possibly protective.
Conclusion Placing an infant prone or on side on last occasion, secondary prone
position (not placed prone but turned to prone), inexperienced prone sleeping and use of
a duvet, leading to head and body being covered, were shown to be risk factors.
Preventive factors were using a cotton sleeping-sack and a dummy. Even in a low
incidence country, such as the Netherlands, there are indications that further prevention
is possible.
Key words Cot death á Sudden infant death syndrome á Prone position
Abbreviations ECAS European Concerted Action on SIDS á CBS Dutch Central Bureau
of Statistics á FSD face straight down á SID sudden infant death
Eur J Pediatr (1998) 157: 681 ± 688 Ó Springer-Verlag 1998
M. P. L'Hoir (&) á G. Th. J. van Well á S. McClelland
T. Dandachli
W. H. G. Wolters á J. Huber
Wilhelmina Children's Hospital, PO Box 18009,
3501 CA Utrecht, The Netherlands, Fax: 31-30-2320707
A.C. Engelberts
University Hospital Leiden,
Department of Paediatrics, Leiden, The Netherlands
P. Westers
Centre for Biostatistics, University of Utrecht,
Utrecht, The Netherlands
G. J. Mellenbergh
Department of Methodology,
Faculty of Psychology, University of Amsterdam,
Amsterdam, The Netherlands
Introduction
Cot death is the sudden unexplained death of an infant
or young child. When a full post mortem examination
fails to demonstrate an adequate cause of death, the
term sudden infant death (SID) is used. We leave out the
ax ``syndrome'' since there are no signs and symptoms
and the clinical death is, on the contrary, characterized
by the absence of such. Much research into cot death is
focused on epidemiological risk factors which when
avoided might diminish the cot death rate. One impor-
tant risk factor is the prone sleeping position. Although
suggested previously, it was not until the late 1980s that
it came to the fore [1±4]. In the Netherlands, the tradi-
tional sleeping position used to be the alternate side
position. In 1972 advice to place infants prone was fol-
lowed widely after publications in the medical and lay
press [5]. At the end of October 1987 G. A. de Jonge
initiated a nationwide campaign not to place infants
prone to sleep. No preference was given as to side or
supine position. Although cot death rates had begun to
decline from a high in 1984, rates in 1987 further de-
creased from 0.91 to an alltime low of 0.26/1.000 in 1995
[6]. In the same period no signi®cant diagnostic shifts in
statistical registration occurred [7]. In April 1992 the
advice was modi®ed from ``not prone'' to sleep exclu-
sively ``supine''. From 1994 onwards additional recom-
mendations were given, namely discouraging the use of
duvets, pillows and `cot-buers'. In the Netherlands
duvets had become popular in the early part of the
1970s. In 1988 60%, in 1994 77% and in 1996 45% of
the infants slept under a duvet [8]. Prevalence studies,
carried out every other year, showed that putting infants
to sleep in the prone position declined from 60% before
the campaign to 27% in 1988, to 7% in 1996. However,
many babies are presently found in prone position after
having been put to bed on the side or back. In two
earlier cot death studies in the Netherlands in 1984±1987
and 1987±1992 respectively, 11% and 27% of infants
who were found in the prone position had turned to that
position, thus showing the secondary prone position to
be of increased importance in cot death as opposed to
the primary prone position [9, 10].
The cot death incidence in the Netherlands is
presently one of the lowest in the Western industrial-
ized world. However, international cot death ®gures
are dicult to compare because of problems with
de®nition and ascertainment [11]. With such a low cot
death incidence the question arises which of the pre-
viously known factors associated with cot death are
still valid and whet her they are amenable to preventive
strategies. The present study was conducted as part of
the `European Concerted Action on SIDS' (ECAS)
[12]. The aim of this article is to examine relative risks
of placing infants prone and other practices associated
with putting infants to sleep, including bedding and
heating.
Methods
Study design
A case control design was chosen. All general practitioners,
(community) paediatricians, pathologists and midwives in the
Netherlands were informed by letter about the project. They were
requested to inform the research centre as soon as possible after an
infant died suddenly and unexpectedly. Announcements appeared
in more than 15 professional journals and a national press report
was released. Two controls for every case were randomly selected,
matched for date of birth.
Case ascertainment
We intended to include all cot death cases in the Netherlands from
March 1995 to September 1996. Infants older than 7 days and
younger than 2 years who died suddenly and unexpectedly and
whose death was unexplained when ®rst found, were included. Not
included were premature infants who had never left hospital and
babies explicitly taken home to die. The de®nitely non-SID cases
were excluded after three pathologists ®rst independently and later
in consensus, had made their diagnosis. In the Netherlands all
deaths are classi®ed anonymously at the Dutch Central Bureau of
Statistics (CBS). Date of birth and date of death of cot death in-
fants were compared with CBS data to assess completeness of as-
certainment.
Control ascertainment
Two live controls were obtained for each case, born within 1 week
before or after the case. They were selected by the municipal au-
thority in whose district the death had occurred and two from the
list of births in the nearest large urban area (Amsterdam, Rotter-
dam, Utrecht or The Hague). Ideally we would not have liked to
match by geographical area or place of residence; however, in the
Netherlands, for practical purposes, this was unavoidable. An
earlier Dutch study has shown that there was no dierence in the
incidence of cot death and sleeping position in respect of a dierent
degree of urbanisation [9]. Selecting controls only from munici-
pality of birth could possibly have introduced selection bias: in the
rural areas there are fewer ethnic minorities. In case of more than
two replies, two were randomly selected.
Questionnaire
The ECAS questionnaire consisted of 228 questions and was se-
parated into subjects concerning: site of death, factors related to
the health of the baby, maternal factors and factors related to
socioeconomic status. The Dutch version included several addi-
tional questions among which: movement in bed, position of the
face when found prone and use of a sleeping-sack (Fig. 1). All
questionnaires taken from parents of cases and controls were
completed at their home by six interviewers (two researchers and
four medical students) who received repeated special training. The
questions for the control-parents all referred to the day/night be-
fore the interview. Reference sleep is de®ned as the sleeping period
of the control baby that corresponds to the period during which the
index baby died as well as the sleeping period on last occasion of
the cases. Many questions refer to infant care practices occurring
`usually' which was de®ned as the usual routine for the time of the
reference sleep.
682
Statistical analysis
Data were entered with EPI-info and analysed with the Statistical
Package for Social Sciences. Binomial tests were used for com-
parison with national data of the CBS and chi-square tests and
correlation analyses for associations between the factors for cases
and controls separately. Chi-square tests and t-tests were used to
compare case and control groups. Logistic regression analyses were
used to measure the risk of factors adjusted for confounders. Well
known risk factors, established from earlier Dutch retrospective
studies [7±10], literature review and ongoing international research
[12, 13], were considered as confounders: infant's age, parity,
mother's age at ®rst live birth, birth weight, sex, socioeconomic
status, and maternal smoking during pregnancy. Birth weight and
gestational age were closely related and eect modi®cation between
these was investigated. After a factor analysis was performed, so-
cioeconomic status was de®ned by several markers including
schooling and housing. Due to the time interval between death of
the case and the control interview, conditional regression analysis
was dicult to apply. We decided to use unconditional logistic
regression analysis after comparison of conditional and uncondi-
tional logistic regression analyses with and without the factor `age',
which did not result in dierences in the standard error. It has been
demonstrated in cot death studies that conditional and uncondi-
tional logistic regression analyses give similar results [14]. In the
logistic regression analyses age at reference sleep was adjusted for.
A stepwise logistic regression analysis was used to determine the
independent eect of the factors concerning bedding and heating in
relation to sleeping position. We built the model with the con-
founders and the determinants for cot death found in univariate
analyses. In the tabulations `not applicable' and `missing' data are
excluded from analyses. All P-values are two-tailed, unless stated
otherwise. Relative risks are expressed in odds ratios (OR) with
con®dence intervals of 95% (CI 95%).
Results
Response cases
Of 105 infants noti®ed at the research centre, 6 were
excluded according to the criteria and 11 families refused
participation. Of these 11 families the age distribution
did not dier from the response group, there were 8 boys
and 1 girl (2 unknown), 3 belonged to an ethnic minority
group and 2 had a strict religious background. Two non-
response families were known to be drug users. In the
other 88 cases a home-visit was made and the ques-
tionnaire was completed. Postmortem was obtained in
63 of the 88 cases. After the consensus meeting of the
three pathologists, 14 cases were excluded because of
major pathology. The remaining 49 cases, together with
25 cases without postmortem were included in the study;
altogether 74 cases. The mean age was 7 months
(SD 5.10) and for cases <1 year it was 5 months
(SD 3.07). Of the 81 cot death cases that were
booked at the CBS in the R95 and R96 categories of the
ICD-10th revision during the research period, 74 (91%)
cases participated in the study.
Response controls
For every case two controls participated. Of 36 (49%)
we received all four consents of controls, of 32 (43%)
three, and of 6 (8%) two. Due to a matching error at one
municipality two control questionnaires were excluded.
Therefore, 73 cases and 146 controls are included in the
multivariate data analyses.
Matching
All cases and controls were matched for date of birth
within 2 weeks. The median time from the moment of
death to the home interview was 34 days for cases and 77
days for controls, due to ascertainment by municipalities
of the control group. In the analysis age dierence be-
tween cases at the time of death and controls at the time
of interview was adjusted for.
Analyses
Sleeping position
Table 1 shows the risks of the dierent sleeping posi-
tions, of head position and movements in reference
sleep. Cases that had been placed on the side to sleep
were younger compared to controls (mean age of cases
in months 3.11 (SD 2.87), of controls 11.38
(SD 6.54). The same dierence was found for ending
up on the side. Nullipa ra families (cases and cont rols
together) less often placed their child in the prone
postition to sleep, compared to multipara families
(P < 0.01).
Secondary prone sleeping
Turning prone from another position (secondary prone
sleeping) in reference sleep increased the risk for cot
death. Secondary prone sleeping on last occasion by cot
death infants correlated signi®cantly with the following
situational features: face straight down (r 0.43,
P < 0.01), turned 180° (r 0.26, P < 0.01) and head
Fig. 1 Dutch sleeping-sack (`trappelzak'), left: quilted sleeping-sack,
right: plain cotton sleeping-sack
683
and body covered by the bedding when found
(r 0.27, P < 0.05). Turning from supine to prone
happened signi®cantly more often (25 of 29 cases)
compared to turning over from the side position to
prone (4 of 29 cases; P < 0.01).
Boys, both cases and controls, had not been placed
prone more often than girls (neither usually nor in ref-
erence sleep). In reference sleep, male cases turned to
prone from another sleeping position more often than
girls (22 versus 6, P 0.04), while they did not usually
do so (4 versus 2). Of the controls, boys turned to prone
more often than girls, usually (23 versus 8) as well as in
reference sleep (22 versus 7; both P 0.03).
Inexperience of prone position
No experience of turning as well as no or little experi-
ence in lying prone seem to be riskfactors. Two cot death
infants had been placed prone and 19 found prone for
the very ®rst time. Those infants not usually placed
prone and not usually found prone, but found prone on
last occasion have an OR of 17.89. However, infants
that could readily turn over into the prone position
(usually placed non-prone, but usually found prone)
seem to have a lower risk for cot death (OR 0.48
(95% CI 0.64±6.89)), although statistical signi®cance
was not reached.
Found face straight down
For cases, ®nding the infant with the face straight down
(FSD) was related to age. The mean age of the 12 cot
death infants found with their face straight down, was 10
months (SD 4.25). Face down position correlated
with seco ndary prone sleeping position (r 0.43,
P < 0.01), but more striking is that 11 of the 12 infants
who were found FSD belong to the group of infants who
were inexperienced in respect of lying prone, while 15 of
41 infants found not face down, were inexperienced
prone sleepers (P < 0.01). Apparently bedding had little
to do with ending up face down as in 9 of the 12 cases
the heads were not covered by bedding; 7 of these 9 did
not have any bedding at all when placed to sleep.
Moved downwards and rotated
Finding that the infant had moved downwards, towards
the foot of the bed, occurred more often in cot death
infants than in controls and correlated with head and
body being covered by the bedding (r 0.48,
P < 0.01). Rotating horizontally, which is de®ned as
turning 90°, happened more often in controls and ap-
peared to reduce the risk.
Changed sleeping position
When we compare how infants are usually placed and
are usually found, cot death infants changed position
less frequently than controls (26% (19) versus 44% (65)),
although statistical signi®cance was not reached
(OR 1.45 (95% CI 0.65±3.29)). On the other hand,
before dying, cases turned more frequently than controls
and more importantly, far more frequently than was
usual for them, which increased the risk of dying
(OR 3.17 (95% CI 1.34±7.50)) (Table 1).
Bedding, dummies and heating
A duvet seemed to increase the risk and the use of
blankets seemed to reduce the risk of cot death, although
for both, statistical signi®cance was not reached
Table 1 Sleeping position,
head position and movements
of cot death cases and controls
in reference sleep (adjusted for
confounders
a
)
Cases Controls Odds ratio (95% CI)
Placed
supine 39 55% 125 87% 1
on side 15 21% 11 8% 4.03 (1.36±11.96)
prone 17 24% 7 5% 8.36 (2.65±26.42)
Found
supine 10 14% 83 62% 1
on side 14 20% 15 11% 8.27 (2.49±27.51)
prone 46 66% 35 26% 18.73 (6.86±51.14)
Primary prone sleeping
b
17 24% 6 4% 7.45 (2.29±24.28)
Secondary prone sleeping
c
29 41% 31 21% 5.05 (2.07±12.34)
Inexperienced prone sleeping
d
28 40% 6 4% 17.89 (5.98±53.48)
Face straight down 12 22% 3 4% 11.18 (2.04±68.58)
Moved downwards 14 22% 11 8% 4.05 (1.66±9.88)
Rotated 4 6% 32 25% 0.12 (0.03±0.47)
Changed sleeping position 34 46% 60 41% 3.17 (1.34±7.50)
a
Infant's age, multiparity, maternal age at ®rst live birth, birth weight, sex, socioeconomic status,
maternal smoking during pregnancy
b
On last occasion placed prone and found prone
c
On last occasion not placed prone but found prone
d
Not usually placed prone and not usually found prone, but after reference sleep found prone
684
(Table 2). For cot death infants there was a close cor-
relation between using a duvet and being found head
and body covered by bedding (r 0.43, P < 0.01) and
this combination constituted an increase in risk.
Sleeping-sack
The use of a sleeping-sack reduced the risk of cot death
(OR 0.30). Analysing the eect of a cotton sleeping-
sack separately from a quilted one, showed a risk re-
ducing eect of the cotton one (OR 0.35), whilst no
statistical signi®cance for the quilted sack was reached.
The use of a sleeping-sack correlated with placing in-
fants supine (r=0.25, P < 0.01) and prevented turning;
of 40 cases without a sleeping-sack, 25 turned in refer-
ence sleep and of 25 with a sleeping-sack only 8 turned
(P 0.02). Controls also usually turned less often from
one sleeping position to another when in a sleeping-sack
(P 0.02). Cases and controls who usually turned over
while in a sleeping-sack were older than 8.5 months. Of
14 cot death cases with a low birth weight (<2500 g),
only 1 slept in a sleeping-sack compared to 20 out of 56
cases with a higher birth weight (P < 0.05). For con-
trols this association was not found.
Dummy use
Cases were placed to sleep with a dummy less often than
controls both usually and in reference sleep. Dummy use
decreased the risk for cot death (OR 0.19). Usually
not placing an infant to sleep with a dummy correlated
with ®nding the baby head and body covered (R=0.11,
P < 0.01). The use of a dummy is related to parity, both
in cases (57% of ®rst born cases versus 21% of not-®rst
born cases; P 0.01) and in controls (62% versus 42%;
P 0.02).
Heating
No dierences were found between cases and controls in
room heating and outdoor temperature. More parents of
cases than controls kept the window closed (Table 2).
The amount of tog values used in reference sleep did not
in¯uence the risk for cot death as long as the infant's
head was not covered by the bedding (One tog unit is the
thermal resistance of a fabric when the temperature
dierence between its faces is 0.1 °C for a ¯ow of heat
equivalent to 1 W/m
2
). Cases were found covered in
sweat more frequently than controls (26% versus 10%).
Dierences in sweating during the last 24 h did not reach
statistical signi®cance. Sweating correlated with togval-
ues r 0.43, (P < 0.01) and with head and body
completely covered by bedding (r 0.44, P < 0.01).
Head and body covered
Cases were more often fou nd with head and body cov-
ered by bedding than controls (Table 2). Cases who were
found head and body covered by bedding diered from
cases who were found head uncovered in respect of
moving downwards, duvet use and high tog values
(P < 0.01). All but 2 of the 19 cot deaths who were
found head and body covered, used a duvet, 9 in addi-
tion slept in a quilted sleeping-sack and 2 in a cotton
one. The age of these 11 was between 7 and 12 months.
Furthermore, all 9 infants who had both a quilted
sleeping-sack and a duvet also had a respiratory tract
infection, according to the parents.
Multivariate model
A logistic regression analysis was performed, incorpo-
rating variables one by one. Risk and preventive factors
found so far were included and selected interactions
were explored. The model (Ta ble 3) was built with the
known confounders and the following determinants
(®rst step): placed prone on last occasion and secondary
prone sleeping. In the next step we incorporated the
cotton sleeping-sack, the duvet and ending up head and
body completely covered . At this stage the sleeping-sack
and the duvet both remained signi®cant; the cotton
sleeping-sack had an OR of 0.27 (95% CI 0.08±0.96),
while the duvet had an OR 3.46 (95% CI 1.01±11.90).
Table 2 Bedding and other fea-
tures in bedroom for cot death
cases and controls in reference
sleep (adjusted for con-
founders
a
)
Cases Controls Odds Ratio (95% CI)
Head and body covered 19 28% 2 2% 27.17 (5.52±133.70)
Duvet 39 55% 68 46% 1.17 (0.56±1.78)
Blanket(s) 18 25% 52 35% 0.79 (0.37±1.66)
Sleeping-sack
quilted 12 18% 50 35% 0.80 (0.54±2.87)
cotton 13 19% 57 40% 0.35 (0.15±0.83)
cotton and quilted 25 37% 107 75% 0.30 (0.13±0.67)
Dummy use 9 12% 70 48% 0.19 (0.08±0.46)
Impermeable mattress 24 34% 27 19% 3.10 (1.42±6.77)
Soft/intermediate mattress 30 41% 32 22% 2.05 (0.99±4.23)
Window closed 64 90% 108 75% 5.40 (1.73±16.79)
a
Infant's age, multiparity, maternal age at ®rst live birth, birth weight, sex, socioeconomic status,
maternal smoking during pregnancy
685
Then we looked for an interaction eect between the use
of a duvet and ending up under the bedding which was
highly signi®cant. The combined eect demonstrated
that ending up under a duvet is risk increasing. When
the interaction eect was added to the model, the cotton
sleeping-sack was no longer signi®cantly protective. In
the ®nal step we added the dummy. The OR of dummy
use during reference sleep was 0.05. This means that
taking into account all known risk factors, dummy use
still seems to have the largest preventive eect, namely it
lessens the risk 20 times.
Population attributable risk
The estimate of the proportion of cases, adjusted for all
other factors, that would in theory not have occurred
had the factor been eliminated, is called the population
attributable risk. For placing the infant prone and on
the side this is 24% and 20% respectively. Preventing
infants from getting trapped under a duvet would de-
crease the amount of cot deaths with 24%. The popu-
lation attributable risk for secondary prone sleeping is
40%. If all infants had been sleeping in a sleeping-sack,
21% of deaths would not have occurred and if dummies
had been used by all infants, in theory, 84% of the cot
deaths would not have occurred.
Discussion
Relative risks of placing infants prone and on the side to
sleep have been examined, together with other practices
associated with putting infants to sleep, such as the use
of duvets, blankets an d sleeping-sacks and the use of a
dummy. A research group of 73 is suciently large re-
garding statistical power in order to use general tests for
comparison of case and control groups. A response of
91% is satisfactory.
In 72% of the cot death cases a postmortem was
performed. Including cases without a postmortem does
not invalidate the study, because we assume that two or
three of the 25 cases without postmortem would have
been explained by postmortem examination [15].
For some cases a long time lag existed between the
death of the infa nt and the time of interview. The me-
dian tim e between cot death and interview was 34 days.
This had dierent logistical reasons. Earlier retrospec-
tive and prospecti ve studies into cot death show that
recall bias because of a time interval between death and
interview, does not in¯uence the results. Studies on the
ability of parents to remember reliably and in great de-
tail what happened around the time of the death of their
baby ha s been well documented [16, 17]. Time between
death of the case and the control interview was longer
due to strict Dutch privacy laws which rule that consent
is solicited via municipal authorities before a control
family may be approached.
Gender
In eight studies into the prevalence of sleeping position,
more boys were placed prone than girls [7, 8]. This was
put forward as part of the explanation of higher male
risk for cot death. Recently it was demonstrated that
boys cry more than girls [18]. Since infants cry less when
kept in prone sleeping position, this might be part of the
reason for putting boys prone. Secondary prone sleeping
however might be part of the present explanation for the
over-representation of boys. Boys turn more frequently
than girls and in reference sleep turn over to prone more
often. Boys apparently have a dierent development of
their motor activity which facilitates turning prone,
probably at a time when the motor development to turn
back is not yet fully developed.
Sleeping position
Even in a country with a low prevalence of prone
sleeping, where 93% of parents place infants supine as
recommended, primary prone sleeping still remains an
important risk factor that increases the risk of dying
almost 7.5 times. Mothers who still place their infant
prone, have a higher parity than mothers who do not
place their infants prone. Placing the infant in the side
position carries an intermediate risk of cot death be-
tween supine and prone sleeping [19]. Moreover, being
found on the side occurs more often in cases than in
controls and therefore it is unlikely that the risk of the
side position is due to turning or falling over to prone
position.
As placing infants prone becomes rare the secondary
prone position carries an increased risk of cot death.
Therefore it is advisable to look for methods of care that
prevent secondary prone position [10]. Infants that were
for the ®rst time either placed pron e or had turned prone
Table 3 Combined risk and preventive factors for cot death (ad-
justed for confounders
a
)
Odds ratio (95% CI)
Placed to sleep on last occasion
supine 1
on side 39.39 (4.46±347.60)
prone 59.17 (7.73±453.03)
Secondary prone sleeping 32.85 (5.16±209.31)
Use of duvet 0.17 (0.04±0.72)
Found head totally covered 1.59 (0.03±31.76)
Interaction duvet use * head
totally covered
38.02 (3.20±452.18)
Use of sleeping-sack 0.73 (0.29±6.43)
Placed to sleep with a dummy 0.05 (0.01±0.29)
All ORs are adjusted for confounders and all the other factors in
the model
a
Infant's age, multiparity, maternal age at ®rst live birth, birth
weight, sex, socioeconomic status, maternal smoking during preg-
nancy
686
and have no experience of `lying prone', have a high risk.
It was striking that all infants found FSD, occurred in
the group of the inexperienced prone sleepers. Some
experience with lying prone is apparently necessary to
ensure that infants turn their head to the side during
sleep, thus keeping mouth and nose free. Recently Wa-
ters et al. [20] studied ten healthy prone-sleeping infants
in their homes using infrared video and cardiorespira-
tory recordings. They studied term infants at age 10 to
22 weeks, who were reported to sleep exclusively in
prone position. Episodes of FSD, with a median dura-
tion of 3.3 min, were initiated and term inated by a
movement/arousal that included head turning. Waters
concluded that the face down position occurs commonly
in healthy prone-sleeping infants. She speculated that
those cot death infants found face down either have a
congenital or an acquired defect in the arousal response
or had to face insurmountable environmental factors
that prevent eective head turning.
Our study demonstrates that cot death FSD cases
were inexperienced pron e sleepers. They were not found
under the bedding and there was no evidence of a
struggle, but somehow they did not arouse. It would be
worthwhile to know whether these infants while awake
had been able to turn their head while prone. If not, this
then would be amenable to training.
Usually not turning prone, but doing so on last
occasion is a risk factor and ®ts our ®nding that cot
death infants usually tended to turn less often from one
position to another compared to controls, the prone
position included. The occurrence of fewer body
movements during sleep, indicating fewer episodes of
arousal, has been found in several studies, including
two prospective ones [21, 22]. Recent studies into the
microsocial environment of cot death infants show that
these infants had lower esti mates of developmental
stimulation, which might lead to passivity [23]. Other
studies of behavioural characteristics also demonstrated
lower activity in cot death infants compared to controls
[24, 25].
Head and body covered
Earlier research showed that ®rm tucking in contributed
to a decreased risk of cot death, while loose wrapping
seemed to enhance the risk [26]. The multifactorial
model shows that the risk of a duvet is getting trapped
under it, with head and body covered.
Our data suggest that in some infants, around the age
of 8 months, the combination of turning prone, moving
downwards, ending up under the bedding and struggling
all are part of the ®nal pathway even though, because of
lack of direct observations, the exact sequence of events
remains unknown.
Preventing infants from turning prone seems relevant
but it appears to us that it would be almost impossible to
restrain infants as old as 8 months. In this group taking
other preventive measurements aimed at other contrib-
uting factors, namely bedding, for example by using only
sleeping-sacks and no other bedding, should be su-
ciently protective.
Hyperthermia
Hyperthermia appears unlikely in the absence of too
much `bedding'. Sweating mainly happened in relation
with a covered face. Windows of cases had been closed
more often and cases more often had used impermeable
mattresses than controls. Outside temperatures and
amount of bedding were similar between cases and
controls. Infections could play a role [27], but we were
not able to demonstrate this in the multivariate model. A
combination of factors seems important, namely ending
up head and body covered by a duvet, while some in-
fants were also in a quilted sleeping-sack and had an
additional infection.
Sleeping-sacks
The widespread usage of sleeping-sacks (about 75%)
might be part of the explanation why the cot death in-
cidence is very low in the Netherlands. It has several
advantages. Firstly, it leads to placing infants in supine
position. Infants are automatically put to sleep on their
back, since the zipper is on the front. Secondly, it pre-
vents infants from turning prone at too early an age
when they are not ready for it. Infant s older than about
8.5 months are usually able to turn, in spite of the
sleeping-sack.
A cotton sleeping-sack is protective. Without extra
bedding a quilted sack is probably also protective. A
sleeping-sack might prevent infants from moving
downwards and thus ending up under the bedding. Fi-
nally less bedding is necessary, which would prevent
hyperthermia. The use of a quilted sleeping-sack to-
gether with a duvet should be strongly discouraged. The
use of a sleeping-sack should be particularly promoted
for infants with a low birth weight.
Dummy use
We found, as in New Zealand and Great Britain, a
protective eect of the dummy [13, 28]. In our study this
eect was found for usual as well as for reference sleep.
Since the eect of the use of a dummy is independent of
sleeping position and many other risk factors, hy po-
thetically several mechanisms could be responsib le.
Firstly a mechanical eect: the presence of a paci®er in
the mouth might prevent the infant from turning their
face straight down and thus preventing obstruction of
mouth and nose. Sec ondly, an acquired eect could be
responsible: an infant who has a paci®er automatically
will keep its nose free of bedding in order to breath.
Thirdly, it may be a matter of classical or operant
687
learning eects: a dummy satis®es sucking. Moving in-
creases the risk of losing the paci®er (a negative rein-
forcer), remaining more or less in position is rewarding
(a positive reinforcer). Our data suggest that dummy use
keeps infants from ending up under the bedding. An-
other explanation could be a slightly raised CO
2
level,
which is a respiratory stimulant and keeps the infant
aroused [29]. In addition, a paci®er might quieten a
possibly restless infant, which prevents the child from
turning and ending up under the bedding. Finally the
stimulation of the upper airway muscle tone by the
sensory input of the sucking could be of importance.
This might keep the tongue forward and maintain upper
airway patency [28]. Especially bottle-fed infants, who
have an increased sucking need, might bene®t from a
dummy.
The fear that dummy use might stand in the way of
breastfeeding is irrelevant to cot death cases, because
most cot death mothers did not breastfeed their infants
anyhow. In the Netherlands in general many mothers
discontinue breastfeeding after 3±4 mont hs; only 30% of
babies are breast-fed longer than 12 weeks, and only
10% of Dutch cot death mothers do so.
In conclusion, even in a low incidence country such as
the Netherlands, there are clear indications that further
preventive measures are possible. Prone sleeping is still a
major risk factor for cot death. Besides being placed
prone, turning to prone and inexperience of prone po-
sition emerge as hazardous. Ending up under a duvet
increases the risk for dying more than heavy bedding per
se. A sleeping-sack, a typical Dutch garment, reduces the
risk by preventing turning and when used, less bedding is
needed. The use of dummies should be recommended, at
least for bottle-fed babies.
Acknowledgements We are indebted to all parents as well as
K. Helweg-Larsen (MD), Priv. Doz. Dr. T. Bajanowski, Dr.
O. Huber-Bruning (MD). We acknowledge the `National working
group cot death'. We also would like to thank the Koninklijk
Meteorologisch Instituut (KNMI) in de Bilt. This study was sup-
ported by the Praeventie Fonds, `s-Gravenhage, The Netherlands.
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688
  • ... We examined 17 observational studies ( Table 1) and found that breastfeeding was reported to have provided a protective effect on SIDS in ten studies (6)(7)(8)(9)(10)(11)(12)(13)(14)(15). No protective effects were found in the other seven (4,(16)(17)(18)(19)(20)(21). ...
  • ... However, such soft bedding can increase the potential of suffocation and rebreathing. 54,56,57,179-181 Pillows, quilts, comforters, sheep- skins, and other soft surfaces are haz- ardous when placed under the in- fant 62,147,182-187 or left loose in the infant's sleep area 62,65,184,185,[188][189][190][191] and can increase SIDS risk up to fivefold independent of sleep position. 62,147 Sev- eral reports have also described that in many SIDS cases, the heads of the infants, including some infants who slept supine, were covered by loose bedding. ...
  • ... The increasing prevalence of an asymmetry in posture and/or shape of the head in young infants has been attributed to the successful initiation of the " Safe Sleeping " Campaign to prevent Sudden Infant Death Syndrome [1] [2] [3] [4] [5] [6]. If the asymmetry is not a symptom of an underlying pathology, it can be defined as an idiopathic asymmetry. ...
  • ... L'Hoir et al. [47] found in their study in the Netherlands that male infants were placed to sleep in the prone position more often than females, and were more likely to turn prone from a side sleeping position than females, and suggested that this may be related to the male SIDS excess. However, as shown in Figure 1, the SIDS male fraction remained essentially the same as the recommended sleep position in the US changed from prone (pre-1992) to supine (post-1992), even though the SIDS rate dropped by a factor of three from 1979 to 2005 [6]. ...
    ... Other hypotheses than the X-linkage hypothesis of Naeye et al. [7] for the male excess in SIDS and other causes of infant respiratory mortality have appeared in the literature [45–47]. Finnström [48] reviewed this topic and concluded that “The mechanism behind the excess perimortality rate in male infants is not known. ...
  • ... Pacifiers provided to premature infants reduce the length of hospital stay [21]. In addition, more recently, several studies have shown that the use of a pacifier protects against Sudden Infant Death Syndrome (SIDS) [22] [23] [24] [25] [26]. ...
  • ... Not only were duvets in cases larger, the specific weight was also higher than in controls. The use of a duvet has previously been identified as a risk factor for SIDS [8,30] and may have a higher impact on infants sleeping in a non-prone position [31]. This could be explained by a higher thermal insulation [32] or a higher likelihood of having the face covered by a heavy duvet [33]. ...
    ... Covering has been found to be a risk factor for SIDS in some earlier studies [39][40][41][42][43]. Covering of the head by bedding during sleep is associated with accumulation of CO 2 around the face [33,44], as well as with a higher body temperature and significant changes in autonomic balance [45]. Present advice given to parents includes the fact that infants should not be in a situation where they are able to become covered by bedding [28,29,46]; use of a sleeping bag is one way of achieving a safe situation [30]. ...
  • ... Pacifiers provided to premature infants reduce the length of hospital stay [21]. In addition, more recently, several studies have shown that the use of a pacifier protects against Sudden Infant Death Syndrome (SIDS) [22] [23] [24] [25] [26]. ...
  • ... However, infants placed to sleep in the side position are more likely to roll into the prone position (Markestad et al., 1995;Mitchell & Scragg, 1994;Scragg & Mitchell, 1998). Perhaps partly because of this instability, infants placed to sleep on their side have a higher risk of SIDS than those put to sleep in the supine position (L'Hoir et al., 1998;Mitchell & Scragg, 1994;Scragg & Mitchell, 1998). Mitchell et al. (1997) found that infants placed to sleep in the side position were more than 6.5 times more likely to die of SIDS than those placed to sleep in the supine position. ...
  • ... The sudden infant death syndrome (SIDS) is the sudden death of an infant that remains unexplained despite complete postmortem studies, death scene investigation and case conference. The risk of dying from SIDS is increased when an infant sleeps with the head covered by bedsheets, blankets, quilts, or duvets (Fleming et al. 1996; Kleemann et al. 1999; L'hoir et al. 1998; Ponsonby et al. 1998). In such conditions, the odds ratio for SIDS has been reported to be as high as 21.6 (CI: 6.2–75.0) ...
    ... The finding was more prominent for 12-week-old infants than in younger infants (Ponsonby et al. 1998). The mechanisms responsible for the deaths remained unexplained and were tentatively attributed to mechanical occlusion of the airways (L'hoir et al. 1998; Ponsonby et al. 1998), rebreathing of expired air (Ponsonby et al. 1998) or thermal stress (Fleming et al. 1996; Guntheroth and Spiers 2001; Kleemann et al. 1999; L'hoir et al. 1998). In a previous study, we reported that covering the infant's head with a bedsheet was associated with a significant increase in auditory arousal threshold (Franco et al. 2002). ...
    ... The changes in autonomic control in the head-covered periods could result from thermal stress. Thermal load could be secondary to insulation but also to the heating of the microclimate by breathing (Fleming et al. 1996; Kleemann et al. 1999; L'hoir et al. 1998; Ponsonby et al. 1998). Core temperature in infants was reported to decrease spontaneously during the first 3–5 h of sleep (Lodermore et al. 1991; Tuffnell et al. 1995), unless opposed by environmental factors, such as sleeping with the head covered. ...
  • ... Six more studies confirmed the association between pacifier use and a reduced risk of SIDS. [16][17][18][19][20][21] Not all studies found a difference between cases and controls in "usual" pacifier usage. A seventh study 22 found no difference among SIDS cases and controls for pacifier use "usually" and at the "last sleep." ...
    ... Other authors have suggested that pacifiers should not routinely be discouraged, 16 or should be recommended "at least for bottle-fed infants." 18 The effect of pacifier use on breast-feeding A mother's decision to breast-feed her newborn infant is based on multiple factors. Recent decades have witnessed a trend toward reductions in the initiation and duration of breast-feeding, particularly in developing countries. ...
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