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Very preterm children show impairments across
multiple neurodevelopmental domains by age
4 years
L J Woodward,
1,2
S Moor,
3
K M Hood,
1
P R Champion,
1
S Foster-Cohen,
1,4
T E Inder,
5
N C Austin
1,6
1
Canterbury Child Development
Research Group, Department of
Psychology, University of
Canterbury, Christchurch, New
Zealand;
2
Van der Veer Institute
for Parkinson’s and Brain
Research, Christchurch, New
Zealand;
3
Department of
Psychological Medicine,
University of Otago,
Christchurch, New Zealand;
4
The Champion Centre,
Burwood Hospital, Christchurch,
New Zealand;
5
Departments of
Paediatrics, Neurology and
Radiology, Washington
University School of Medicine,
St Louis, MO, USA;
6
Christchurch Women’s
Hospital, Christchurch, New
Zealand
Correspondence to:
Associate Professor
Lianne Woodward, Canterbury
Child Development Research
Group, Department of
Psychology, University of
Canterbury, Private Bag 4800,
Christchurch, New Zealand;
lianne.woodward@canterbury.
ac.nz
Accepted 6 February 2009
Published Online First
22 March 2009
ABSTRACT
Objectives: Neurodevelopmental outcomes associated
with preterm birth are of major health and educational
concern. This study examined the neuromotor, cognitive,
language and emotional/behavioural outcomes of a
regional cohort of 4-year-old children born extremely
preterm (EPT: 23–27 weeks’ gestation), very preterm
(VPT: 28–33 weeks) and full term (FT: 38–41 weeks). Of
particular interest were children’s risks of impairment
across multiple neurodevelopmental domains.
Methods: Data were gathered as part of a prospective
longitudinal study of 105 very preterm ((33 weeks
gestation) and 107 FT children born during 1998–2000. At
4 years corrected age, children underwent a compre-
hensive multidisciplinary assessment that included a
paediatric neurological examination, cognitive and lan-
guage testing, and an assessment of child emotional and
behavioural adjustment.
Results: At age 4 years, compared to FT children, EPT
and VPT children had increased risks of cerebral palsy
(EPT 18%, VPT 15%, FT 1%), cognitive delay (EPT 33%,
VPT 36%, FT 13%), language delay (EPT 29%, VPT 29%,
FT 10%) and emotional/behavioural adjustment problems
(EPT 37%, VPT 13%, FT 11%). EPT and VPT children were
three times more likely to have multiple domain
impairments than FT children (EPT 30%, VPT 29%, FT
10%).
Conclusions: A substantial proportion of preschool
children born very preterm show clinically significant
problems in at least one neurodevelopmental domain,
with impairment in multiple domains being common.
There is a need to monitor preschool development across
a range of functional domains and to consider the likely
cascading effects of multiple impairments on later
development.
The birth of a premature baby is a stressful time
for parents, with concerns about the future being a
major focus of discussion with clinicians. Accurate
information about potential neurodevelopmental
challenges ahead is essential to providing appro-
priate guidance to parents. It is also invaluable to
developmental surveillance teams responsible for
follow-up visits and the timely introduction of
intervention services.
12
This is important since
converging evidence shows that despite gains in
survival, rates of longer term morbidity remain
high amongst children born very preterm, with 5–
15% experiencing motor deficits such as cerebral
palsy,
34
and a further 25–50% developing clinically
significant difficulties that will impact their
educational progress and family life. Such
difficulties include intellectual delay,
5
speech/
articulation problems,
6
ADHD
57
and specific learn-
ing disorders affecting reading, writing and mathe-
matics.
89
These risks increase with decreasing
gestational age at birth.
10
Although these longer term consequences of
preterm birth have been well described, much less
is known about the early emergence of these
difficulties prior to school entry. Existing infant
and preschool follow-up studies have focussed
largely on the risks and sequelae of severe
neurodevelopmental disabilities such as cerebral
palsy and severe intellectual delay. In contrast,
little consideration is given to other important
domains of development (eg, language, behaviour)
that are also undergoing rapid and complex
development, and which together with motor
and cognitive functioning form the building blocks
of later social, behavioural and academic suc-
cess.
11 12
What is already known on this topic
cExisting preschool studies show that very
preterm children are at elevated risk of severe
neurodevelopmental disability including cerebral
palsy and severe intellectual delay.
cHowever, few studies have assessed functioning
across multiple neurodevelopmental domains or
the extent of less severe but clinically significant
functional impairments.
What this study adds
cNeurodevelopmental risks associated with
preterm birth extend beyond neuromotor and
cognitive functioning to language and
behavioural adjustment during the preschool
period.
cComorbid impairment across multiple
neurodevelopmental domains is common
amongst preschool children born very and
extremely preterm.
cFollow-up studies need to assess children
across a range of neurodevelopmental domains,
so as not to underestimate both current and
future risk.
Original article
Arch Dis Child Fetal Neonatal Ed 2009;94:F339–F344. doi:10.1136/adc.2008.146282 F339
There is some evidence that even before school age, children
born very preterm show signs of language delay,
13
regulatory
and behavioural difficulties
14
and impaired motor function, as
well as general
3
and specific neurocognitive difficulties.
15
Although these studies have highlighted key areas of impair-
ment, few have examined the impacts of preterm birth across
multiple neurodevelopmental domains. Consequently, the
extent and nature of comorbid impairments within this
population remain unclear. This issue is of clinical importance
for two reasons. First, it is possible that the assessment of a
single or narrow range of domains may underestimate a child’s
developmental problems.
16
Second, it is highly likely that
children subject to multiple domain impairments will experi-
ence greater functional difficulties in everyday life, as well as a
poorer long term prognosis than children with no or single
domain impairments.
17
Drawing on prospective longitudinal data from a regional
cohort of children born very preterm in Christchurch, New
Zealand, the aims of this study were:
(1) To assess the extent and patterns of neuromotor, cognitive,
language and emotional/behavioural impairment at age
4 years amongst children born extremely preterm, very
preterm and full term.
(2) To examine relations between gestational status at birth
and children’s later risk of impairment across multiple
neurodevelopmental domains spanning neuromotor func-
tion, cognition, language and emotional/behavioural adjust-
ment.
METHODS
Participants
Study participants consisted of two groups of children. The first
group was a regional cohort of 105 children born very preterm
((33 weeks’ gestation) who were consecutively admitted to a
level III neonatal intensive care unit (NICU) at Christchurch
Women’s Hospital (New Zealand) over a 2-year period
(November 1998–December 2000). The second group of study
children, recruited at age 2 years, consisted of a sample of 107
full term children matched to the very preterm cohort for
gender, place and date of birth.
Preterm children had a mean gestational age of 28 weeks
(range: 23–33) and a mean birth weight of 1050 g (range: 440–
1790 g). In total, 92% of eligible infants were recruited at birth.
Excluding deaths (n = 3), 98% were followed up to age 4. An
additional child (blind) was not assessed on all measures. Since
prior research shows that those born at earlier gestational ages
may be especially vulnerable to later neurodevelopmental
challenges,
10
preterm children were divided into two groups:
those born extremely preterm (EPT: 23–27 weeks’ gestation,
n = 43) and those born very preterm (VPT: 28–33 weeks’
gestation, n = 62).
The full term born children (FT: 38–41 weeks’ gestation)
were identified from hospital birth records for the same period
by alternately selecting, in a forwards and backwards fashion,
the second child listed in the delivery schedule. Of those
identified, 62% were recruited at age 2. Reasons for non-
participation included untraced (47%), moved overseas (12.5%),
refused (12.5%) and agreed but couldn’t attend clinic appoint-
ment/s within the 4-week assessment window due to illness or
family circumstances (28%). Comparison of the socioeconomic
profile of families in the FT group with regional census data
18
showed that these families were highly representative of the
region from which they were recruited. Retention to age 4 was
96%. Data for one additional child were excluded due to
incompleteness. A descriptive profile of the infant medical and
family background characteristics of the three study groups is
provided in table 1.
Measures
Information relating to each child’s antenatal, perinatal and
postnatal course was collected from clinical notes, hospital
databases and parent interviews at term, 2 and 4 years. At
corrected age 4 years (¡2 weeks), all children underwent a
comprehensive multidisciplinary assessment of neuromotor
functioning, cognition, language and emotional/behavioural
adjustment. With the exception of cerebral palsy, clinical
impairment was determined on the basis of the score distribu-
tions of our regionally representative control group. This
approach avoided problems associated with the use of norma-
tive test data.
19
All procedures and measures were approved by
our regional ethics committee and written informed consent
was obtained from all parents/guardians.
Neuromotor functioning
The quality of children’s motor skills, coordination, gait and
behaviour was assessed by an experienced paediatrician.
Cerebral palsy was diagnosed using standard criteria including:
(a) anatomic location/body parts impaired (eg, hemiplegia,
diplegia); (b) degree of impairment to muscle tone and reflexes;
and (c) severity of impact on ambulation.
20
Cognitive ability
A short form of the revised Wechsler Preschool and Primary
Scales of Intelligence test (WPPSI-R)
21
provided a standardised
measure of general cognitive ability. This measure consisting of
two verbal (Comprehension and Arithmetic) and two perfor-
mance (Picture Completion and Block Design) subtests has been
shown to be reliable and to correlate well with the full WPPSI
(r = 0.89–0.92).
22
Cognitive delay was defined as an IQ score
.1 SD below the mean for the FT group. This criterion
included children with both mild (.1 SD and (2 SD) and
severe (.2 SD) delays.
Language development
The preschool version of the Clinical Evaluation of Language
Fundamentals test (CELF-P)
23
was used to measure children’s
expressive, receptive and overall language ability. This measure
is internally consistent, has good test–retest reliability and
correlates highly with other language scales.
24
Expressive,
receptive and overall (total) language delay was defined as a
standard score .1 SD below the mean for the FT group. This
definition spanned both mild (.1 SD and (2 SD) and severe
(.2 SD) delay.
Emotional and behavioural adjustment
The parent report Strengths and Difficulties Questionnaire
(SDQ)
25
measured the extent to which children were subject to
emotional problems, hyperactivity/inattention, conduct pro-
blems and peer relationship problems. Overall behavioural
adjustment was also assessed by summing children’s scores on
the emotional problems, hyperactivity/inattention and conduct
problems subscales. The SDQ correlates highly with other
established measures of child behaviour.
26
Given the young age
of study children, impairment was defined utilising a worst 10%
cut-point.
14
Based on the score distributions for the FT group, a
subscale score equal to or greater than the 90th percentile was
defined as a clinically significant problem (emotional problems
Original article
F340 Arch Dis Child Fetal Neonatal Ed 2009;94:F339–F344. doi:10.1136/adc.2008.146282
.3; hyperactivity/inattention .5, conduct problems .4; peer
problems .3 for girls, .2 for boys).
RESULTS
Neurodevelopmental impairment at age 4
Table 2 shows the neuromotor, cognitive, language and
emotional/behavioural outcomes of children born extremely
preterm (EPT: ,28 weeks’ gestation), very preterm (VPT: 28–
33 weeks’ gestation) and full term (FT: 38–41 weeks) at 4 years
corrected age. Outcomes for the total sample of VPT children
are also reported. Across all domains, children born extremely
and very preterm were at increased risk of later problems
relative to FT children. The extent and severity of later
problems also increased with decreasing gestational age. These
findings were robust to statistical control for family socio-
economic status. For each neurodevelopmental domain, the
results in table 2 were as follows.
Table 1 Characteristics of the sample
Outcome
All preterm,
23–33 weeks’ GA
(n = 105)
Extremely preterm,
,28 weeks’ GA
(n = 43)
Very preterm,
28–33 weeks’ GA
(n = 62)
Full term,
38–41 weeks’ GA
(n = 107) F/x
2
p Value
Child clinical characteristics
Mean (SD) birth weight 1061.60 (310.94) 807.51 (233.67) 1237.82 (223.97) 3574.50 (409.84) 1534.51 ,0.001
% Male 50.5 46.5 53.2 55.6 1.01 0.60
% Singletons 65.7 72.1 61.3 96.3 34.59 ,0.001
% Small (,2 SD) for GA 10.5 16.3 6.5 0.9 13.75 0.001
% Oxygen at 36 weeks 34.3 65.1 12.9 0.0 96.14 ,0.001
% Intraventricular haemorrhage grade III/IV
and/or PVL
10.5 16.3 6.5 0.0 16.22 ,0.001
% Any postnatal corticosteroid use 10.5 23.3 1.6 0.0 34.49 ,0.001
% Patent ductus arteriosus 43.8 65.1 29.0 0.0 81.78 ,0.001
Family characteristics
Mean (SD) maternal age 30.83 (5.34) 31.02 (5.89) 30.69 (4.98) 31.02 (4.48) 0.10 0.91
% European ethnicity 86.7 83.7 88.7 88.0 0.65 0.72
% Single parent family 18.6 21.4 16.7 11.3 2.63 0.27
Family SES*
Professional/managerial 26.7 25.6 27.4 36.1
Technical/skilled 43.8 48.8 40.3 53.7
Semi/unskilled/unemployed 29.5 25.6 32.3 10.2 13.65 0.008
GA, gestational age; PVL, periventricular leukomalacia; SES, socioeconomic status.
*Family SES was assessed using the revised Elley and Irving Socio-Economic Index.
31
Table 2 Neuromotor, cognitive, language and behavioural adjustment outcomes at age 4 years of children born extremely preterm, very preterm and
full term
Outcome
All preterm
(n = 105)
Extremely preterm
(n = 43)
Very preterm
(n = 62)
Full term
(n = 107) F/x
2
p Value
Neuromotor
% Cerebral palsy 16.2 18.6 14.5 0.9 16.58 ,0.001
Cognitive ability
Mean (SD) WPPSI-R IQ score 94.91 (15.45) 93.86 (17.57) 95.65 (13.88) 104.70 (13.45) 12.28 ,0.001
% Cognitive delay 34.3 32.6 35.5 13.1 13.34 0.001
Language development*
Mean (SD) receptive language score 90.70 (12.22) 90.26 (12.75) 91.00 (11.96) 97.53 (13.10) 7.36 0.001
% Receptive language delay 30.0 34.1 27.1 15.2 7.10 0.03
Mean (SD) expressive language score 93.60 (13.47) 93.62 (13.94) 93.60 (13.28) 99.09 (13.17) 4.28 0.02
% Expressive language delay 25.0 22.0 27.1 12.4 5.83 0.05
% Overall language delay 31.0 31.7 30.5 15.2 7.22 0.03
Emotional and behavioural adjustment{
Mean (SD) emotional problems score 2.03 (1.78) 2.35 (1.86) 1.80 (1.70) 1.42 (1.40) 5.34 0.006
% Emotional problems 16.5 23.3 11.7 6.5 8.47 0.01
Mean (SD) conduct problems score 2.66 (2.10) 2.81 (2.39) 2.55 (1.88) 2.21 (1.77) 1.61 0.20
% Conduct problems 16.5 23.3 11.7 14.0 2.86 0.24
Mean (SD) hyperactive/attentional problems score 3.86 (2.55) 4.42 (2.90) 3.47 (2.21) 2.93 (2.23) 6.03 0.003
% Hyperactive/attentional problems 24.3 37.2 15.0 11.2 14.68 0.001
Mean (SD) peer problems score 1.62 (1.75) 2.28 (2.06) 1.15 (1.31) 1.16 (1.44) 8.93 ,0.001
% Peer relationship problems 20.4 27.9 15.0 10.3 7.38 0.03
Mean (SD) total difficulties score 10.17 (5.86) 11.86 (6.47) 8.97 (5.10) 7.73 (4.49) 9.98 ,0.001
% Overall behavioural difficulties 23.3 37.2 13.3 11.2 15.45 ,0.001
WPPSI-R, revised Wechsler Preschool and Primary Scales of Intelligence.
*Excludes two extremely preterm (not assessed), three very preterm and two FT children whose families chose not to complete the additional language assessment.
{Excludes two very preterm (twin) children for whom parent questionnaire data were not returned.
Original article
Arch Dis Child Fetal Neonatal Ed 2009;94:F339–F344. doi:10.1136/adc.2008.146282 F341
Neuromotor
For cerebral palsy, 19% (n = 8/43: 4 mild, 2 moderate, 2 severe)
of EPT, 15% (n = 9/62: 5 mild, 3 moderate, 1 severe) of VPT and
one FT child (mild) were diagnosed with this condition by age 4.
Since our 2-year evaluation, an additional three preterm and one
FT child (antenatal antiepileptic exposure) had met criteria for
mild cerebral palsy. All new cases had an abnormal neurological
examination previously. Three children (2 EPT, 1 VPT) with
severe cerebral palsy at age 2 were diagnosed as moderate at
age 4.
Cognition and language
With respect to cognitive development, 33% (n = 14/43: 9 mild,
5 severe) of EPT and 36% (n = 22/62: 17 mild, 5 severe) of VPT
children were delayed compared to only 13% (n = 14/107: 12
mild, 2 severe) of FT children. Preterm children were also
characterised by high rates of overall language delay, with
nearly a third of EPT (32%, n = 13/41: 7 mild, 6 severe) and VPT
children (31%, n = 18/59: 16 mild, 2 severe) being delayed
compared to FT children (15%, n = 16/105: 14 mild, 2 severe).
Receptive delay was more common than expressive delay
amongst EPT children.
Emotional and behavioural adjustment
The most frequently reported problem amongst preterm
preschoolers was hyperactivity/inattention, with 37% (n = 16/
43) of EPT and 15% (n = 9/60) of VPT children obtaining scores
above the 90th percentile. The next most common area of
difficulty was peer relationship problems (EPT 28%, n = 12/43;
VPT 15%, n = 9/60) followed by emotional problems (EPT 23%,
n = 10/43; VPT 12%, n = 7/60), with risks being greatest for
EPT children. No significant differences were found for conduct
problems (p = 0.22). In terms of overall behavioural adjustment,
more than a third of EPT children (37%, n = 16/43) obtained a
total difficulties score in the clinical/abnormal range compared
to 13% (n = 8/60) and 11% (n = 12/107) of VPT and FT
children, respectively.
Extent and nature of comorbid patterns of impairment
To examine the extent to which children born very preterm and
extremely preterm were subject to impairment across multiple
neurodevelopmental domains, the number of domains impaired
was summed for each child using the following measures:
cerebral palsy, cognitive delay, language delay and a total
SDQ emotional/behavioural adjustment score >14 (10th
percentile cut-point). To minimise data loss, children with
missing data in one domain were assigned a score of 0 (no
impairment) unless clear impairment was evident at ages 2 and
6 years (n = 1 VPT child with severe and persistent behaviour
problems).
Table 3 shows that across all domains, only 40% of preterm
children were free of any impairment compared to 74% of full
term children at 4 years. When examined by gestational status,
EPT children were the least likely to be free of impairment
(33%), followed by VPT (45%) and then FT children. Comorbid
patterns of impairment were also more common amongst
children born extremely preterm and very preterm, with almost
a third of both groups exhibiting clinically significant impair-
ment in two or more neurodevelopmental domains.
The patterns of comorbidity observed within each group are
shown in fig 1. Overall, 67% of EPT, 55% of VPT and 26% of FT
children exhibited problems in at least one neurodevelopmental
domain (table 3, fig 1). For all groups, comorbidity was
particularly marked amongst children with cerebral palsy
(EPT: n = 7/8; VPT: n = 6/9; FT: n = 1/1). However, even
excluding these children, comorbidity was common across
neurodevelopmental domains.
DISCUSSION
This study examined the neurodevelopmental outcomes of a
regional cohort of 4-year-old children born very preterm. Of
special interest was the extent to which children born extremely
and very preterm were subject to impairments across multiple
neurodevelopmental domains and the nature of these comor-
bidities. Study strengths included the prospective longitudinal
research design, the unselected nature of the preterm sample,
our demographically representative comparison group, high
sample recruitment and retention, and the examination of a
diverse range of functional outcomes.
Results confirm the presence of high rates of neurodevelop-
mental impairment amongst preschool children born very
preterm spanning neuromotor functioning, cognition, language
and emotional/behavioural adjustment. By 4 years corrected
age, 16% of preterm children met clinical criteria for cerebral
palsy, a third showed mild/severe cognitive delay and between a
quarter and a third had delayed receptive or expressive language
development. Rates of emotional and behavioural problems
were also high, ranging from 16% to 24%, with hyperactivity/
inattention being most common, followed by peer relationship
difficulties and emotional problems. These elevated rates of
emotional problems may reflect emotional regulatory difficul-
ties
27
and/or the early emergence of internalising problems.
Finally, as previously demonstrated,
10
neurodevelopmental risks
were greatest for children born extremely preterm, especially
with respect to cerebral palsy and behavioural adjustment. EPT
children also tended to be subject to more severe impairment.
These findings are generally consistent with existing preschool
studies documenting high rates of severe neurodevelopmental
disability,
28 29
as well as those examining specific impairments in
cognition and behaviour.
14 30
Expanding on existing research, we also examined the extent
to which EPT and VPT children were subject to impairments
across multiple neurodevelopmental domains. Findings showed
that only 40% of all preterm children were free of any
impairment. Amongst those with impairment in one domain,
Table 3 Number of neurodevelopmental domains impaired at age 4 years
Number of domains
impaired
All preterm
(n = 105)
Extremely
preterm
(n = 43)
Very preterm
(n = 62)
Full term
(n = 107) x
2
p Value
0 40.0 32.6 45.2 73.8
1 30.5 37.2 25.8 15.9
2 19.0 16.3 21.0 6.5
3 6.7 7.0 6.5 3.7
4 3.8 7.0 1.6 0.0 33.43 ,0.001
Original article
F342 Arch Dis Child Fetal Neonatal Ed 2009;94:F339–F344. doi:10.1136/adc.2008.146282
almost half were experiencing difficulties in another. Within the
FT group, most children who showed impairment did so in only
one domain. One other study of 5-year-old children born very
preterm (,30 weeks) also found that only 39% scored in the
normal range on measures of neurological, motor, cognitive and
behavioural functioning, with nearly half (44%) scoring below
age norms in two or more developmental domains.
17
Whilst
informative, no full term comparison data were available and
the nature of the comorbid impairments was not reported in
this study.
In contrast, our analyses showed that across all groups,
children with cerebral palsy were characterised by high rates of
comorbid cognitive, language and behaviour problems.
However, multiple impairments were not unique to these very
high risk children but were shared to a lesser extent by other
EPT and VPT children. Examination of the patterns of
impairment amongst preterm children also revealed high levels
of comorbidity between cognitive and language delay, likely
reflecting their functional inter-dependence as well as shared
processing demands. However, in the interpretation of these
findings it is important to note that this analysis did not
consider comorbidities within the psychosocial domain such as
between attentional and conduct problems. Nonetheless,
findings do suggest that the assessment of a limited range of
functional outcomes is likely to underestimate the extent of a
child’s problems. They also raise concerns about the extent to
which multiple domain impairments may increasingly limit
children’s learning opportunities and have potentially cascading
effects on development over time.
Finally, several measurement issues are worthy of note. First,
our analyses lend support to concerns about the use of outdated
test norms for defining neurodevelopmental delay.
19
Examination of our data using test norms revealed considerable
variability across measures, with some measures greatly under-
estimating risk (eg, WPPSI-R) and others producing similar
results to those based on our comparison group (eg, CELF-P). A
second issue concerns the choice of clinical cut-points across
domains, since these can vary across measures. To optimise
comparability with other studies, we defined impairment using
established clinical criteria for each domain rather than apply a
uniform criterion. However, as part of this approach, cut-points
were selected to ensure base rates were similar across the
cognitive, language and behavioural domains (11–15%).
Nonetheless, further follow-up of this cohort will be important
in establishing the longer term clinical significance of these
classifications as well as the prognostic significance of multiple
domain impairment.
In conclusion, study results clearly demonstrate that neuro-
developmental problems are common and detectable before
school entry. They also raise serious concerns about the
preparedness of many preterm children, especially those with
multiple impairments, for the cognitive, behavioural and
interpersonal challenges of the classroom. As such, these
findings have a number of implications for neonatal follow-up
Figure 1 Patterns of impairment found at age 4 years in each study group. (A) Patterns for children born extremely preterm, very preterm and full
term. (B) Overall summary for the total sample of very preterm children in comparison with the full term group.
Original article
Arch Dis Child Fetal Neonatal Ed 2009;94:F339–F344. doi:10.1136/adc.2008.146282 F343
and educational services. First, careful assessment of a child’s
developmental status, including both strengths and weaknesses,
will be important in assisting parent–teacher discussions about
how learning can best be supported. Second, early childhood
and primary school teachers, alongside other professional
groups, need to be skilled in the early identification and
effective management of the learning and behavioural disorders
that affect preterm children.
Acknowledgements: Special thanks to Jacqueline Knight and Carole Spencer for
assistance with data collection and to study families for their time and support of this
project.
Funding: This research was funded from grants from the Neurological Foundation of
New Zealand, Research Council of New Zealand, Canterbury Medical Research
Foundation, and the Lottery Grants Board.
Competing interests: None.
Ethics approval: All procedures and measures were approved by the regional ethics
committee.
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Original article
F344 Arch Dis Child Fetal Neonatal Ed 2009;94:F339–F344. doi:10.1136/adc.2008.146282
