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Research
Is sudden infant death syndrome still more common in very low
birthweight infants in the 1990s?
Beverley Sowter, Lex W Doyle, Colin J Morley, Anne Altmann and Jane
Halliday
MJA 1999; 171: 411-413
Abstract -
Introduction -
Methods -
Results -
Discussion -
References -
Authors' details
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Abstract |
Objective: To determine the rate of sudden infant
death syndrome (SIDS) in very low birthweight children (VLBW)
relative to children with low (LBW) and normal birthweights.
Design, setting and subjects: Cohort study of
consecutive live births in Victoria, 1993-1997 inclusive.
Main outcome measures: All sudden unexpected deaths
in early childhood over this five-year period; all deaths from SIDS
(defined as a sudden unexpected death without a definite
pathological explanation); and the proportion of SIDS in live births
in three birthweight subgroups (VLBW, 500-1499
g; LBW, 1500-2499
g; and normal birthweight, >
2499 g).
Results: There were 316
028 live births (with known birthweight) in Victoria
over the five-year period; 224 (0.71 per 1000 live births) died
unexpectedly. In 10 of these deaths there was a definite pathological
explanation, giving a rate of SIDS of 0.68 per 1000 live births. The
rate of SIDS in VLBW children was 2.52 per 1000 live births, lower than
the rate reported before the 1990s. The rate of SIDS in VLBW children
was not significantly different from the rate in LBW children of 1.98
per 1000 live births (difference per 1000 live births, 0.53; 95% CI,
21.45 to 2.52), but was significantly higher than the rate in normal
birthweight children of 0.59 per 1000 live births (difference per
1000 live births, 1.93; 95% CI, 0.06-3.79).
Conclusions: The rate of SIDS in VLBW children has
fallen in the 1990s, along with the overall fall in the rate of SIDS, but
remains higher than that in normal birthweight children.
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| | Introduction |
Most parents learn to live with the fear that their baby may die of
sudden infant death syndrome (SIDS). However, the fear of SIDS can be
even greater for parents of babies with low birthweight, or those with
babies who have been in intensive care or who have had apnoea. Before
discharge, many parents attend education sessions on reducing the
risks of SIDS and on infant resuscitation. At one of these sessions the
parents may ask the difficult question: "Is my baby more likely to
die of SIDS because he (or she) was so tiny when born?".
Before the 1990s, children with very low birthweight (VLBW,
500-1499 g) were known to have a
higher rate of SIDS than those with a normal birthweight
(> 2499
g).1-3 With the advent of
preventive measures, the overall rate of SIDS in Australia has fallen
dramatically in the 1990s (from 1.87 per 1000 live births in 1990 to
0.78 per 1000 live births in 1995).4 However, it is unclear
whether the rate of SIDS has also fallen in VLBW children. We aimed to
determine the rate of SIDS in the 1990s for VLBW children relative to
children of other birthweights (low birthweight [LBW],
1500-2499 g; and normal
birthweight, >
2499 g).
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Methods |
We studied a cohort of all consecutive live births in Victoria during
the five-year period from 1993 to 1997, inclusive, and recorded all
sudden deaths in early childhood (divided into the first 28 days [the
neonatal period], postneonatal infancy [29-365 days], and early
childhood [more than 1 year]). SIDS was defined as a sudden unexpected
death without definite pathological features to explain the death.
In the SIDS group, some children were considered by the pathologist to
have pathological features, but these were insufficient to explain
the death. Some had only a minor condition, and in the remainder no
pathological features were found. All births with unknown
birthweight were excluded.
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Data sources |
Data on deaths were obtained from the annual reports of the
Consultative Council on Obstetric and Paediatric Mortality and
Morbidity,5-9 a government-legislated
surveillance body. The Council collects data on all perinatal deaths
from 20 weeks' gestation, and all infant and child deaths up to 14 years
of age. Death registrations are forwarded directly from the Registry
of Births, Deaths and Marriages, and information on all sudden
unexpected deaths is supplemented by the Victorian State Coroner.
These cases are then all reviewed and classified by an expert
pathologist working in the field.
Data on births in Victoria were supplied by the Perinatal Data
Collection Unit of the Public Health and Development Division of the
Department of Human Services. The Unit collects data on all births in
Victoria from 20 weeks' gestation under a legislated notification
system.
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Statistical analysis | |
The proportions of deaths from SIDS (and 95% confidence intervals) in
each of the birthweight subgroups (VLBW, 500-1499 g; LBW, 1500-2499
g; and normal birthweight, > 2499 g) were calculated,10 and comparisons made
between the groups.10 |
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Results |
Over the five-year period 1993-1997, there were 316 028 live births in Victoria for which
birthweight was known. (Birthweight was not known for a total of 90
live births.) Over the same period, there were 224 sudden unexpected
deaths with known birthweight, of which 10 (4.5%) had a definite
pathological explanation, leaving 214 deaths from SIDS (0.68 per
1000 live births). Of these 214 children with SIDS, 23 (10.7%) died in
the neonatal period (including one who died during the primary
hospitalisation), 171 (79.9%) died in postneonatal infancy, and 20
(9.3%) died after the age of 1 year.
VLBW children made up less than 1% of all live births over this period;
the rate of SIDS in VLBW children was 2.52 per 1000 live births (Table).
This was not significantly higher than the rate in LBW children of 1.98
per 1000 live births (difference per 1000 live births, 0.53; 95% CI,
21.45 to 2.52), but was significantly higher than the rate in normal
birthweight children of 0.59 per 1000 live births (difference per
1000 live births, 1.93; 95% CI, 0.06-3.79). LBW children had a
significantly higher rate of SIDS than normal birthweight children
(difference per 1000 live births, 1.39; 95% CI, 0.69-2.09).
Of the seven deaths in VLBW infants, definite pathological features
were found in five, but these were insufficient to explain the death;
three of these infants had respiratory disease (pneumonia,
bronchiolitis, or tracheobronchitis).
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Discussion |
Our study showed no significant difference in the rate of SIDS between
VLBW and LBW infants; however, the rate in each of these subgroups was
significantly higher than in normal birthweight children.
Before recommendations for reducing the risk of SIDS were introduced
in 1991, the SIDS rate was higher in VLBW infants compared with those
with normal birthweight, for both hospital and regional
cohorts. In a VLBW hospital
cohort, 1977-1978, the rate of SIDS before 2 years of age was 30.3 per
1000 live births (7/231);1 and in a regional cohort in
New Zealand (children born in 1986), the incidence of SIDS in the VLBW
group was 13 per 1000 live births, more than three times the rate of 4.0
per 1000 live births for all NZ children born in 1986.2 In a Californian
study of 2962 children dying of SIDS between 28 days and 1 year of age in
1978-1982, the overall incidence was found to be 1.5 per 1000 live
births. The highest incidence was in the VLBW group (7.5 per 1000 live
births), decreasing to 1.3 per 1000 live births for the normal
birthweight group.3
Studies have not shown evidence of a fall in the rate of SIDS in VLBW
infants just before the recommendations were introduced. For
example, in 1985-1991, the rate of SIDS in VLBW infants in the first
year of life for singleton births in the United States remained
relatively constant (average, 3.66 per 1000 live births) compared
with rates for normal birthweight singleton infants (average, 1.07
per 1000 livebirths).11
Studies comparing the period before and after the recommendations
have shown a change in rate of SIDS in VLBW children around the
beginning of the 1990s. One study cited by l'Hoir et al12 estimated the
rate of SIDS in VLBW children in the Netherlands to have decreased from
10 per 1000 in 1983 to 1 per 1000 (presumably live births) in 1995-96, a
change in the rate of SIDS over time similar to that comparing our
results with rates in the late 1980s. A more recent US report
described a smaller reduction in the rate of SIDS in VLBW children
before and after the recommendations about sleeping position, and
the reduction was similar across birthweight subgroups (between
1991 and 1995 reductions of 37%, 36% and 30% were found for birthweight
subgroups 500-1499 g,
1500-2499 g, and
> 2499
g, respectively).13
Avoidance of risk factors probably explains the fall in the rate of
SIDS in VLBW infants in the 1990s, the same reason that it has fallen for
infants overall. The reason SIDS remains more prevalent in VLBW
infants compared with normal birthweight infants may relate to the
underlying pathological features, which were more common in VLBW
infants with SIDS.
So, what should we be telling parents when they ask if their tiny baby is
more likely to die of SIDS?
Firstly, VLBW and LBW children are at increased risk of SIDS.
However, 399 out of 400 VLBW children, and 499 out of 500 LBW children,
do not die of SIDS.
Secondly, parents can help to decrease the risk of SIDS by following
the recommendations: putting their baby to sleep supine, not
smoking, and not allowing the baby to become overheated or covered
over by bedding.4
Thirdly, as most VLBW children who died of SIDS had a definite
pathological condition at autopsy, parents should seek medical
advice early if the baby appears unwell in any way.
Parents often recognise that their baby is unwell, but it is not always
easy for them to decide what is a minor illness and when they need to seek
medical advice. A scoring system such as "Baby Check" 14 can be used both by parents and general
practitioners to help them to determine whether or not a baby is
seriously ill. In a recent review of 37 sudden unexpected infant
deaths, 3 (8%) scored very highly for serious illness on a
retrospective
score with Baby Check, suggesting that such a scoring
system could have identified serious illness before death and led to
appropriate treatment.15 The three VLBW children
with significant respiratory disease in our study probably would
have shown signs of illness before they died.
In conclusion, the rate of SIDS in VLBW children has fallen from over 10
per 1000 live births before the 1990s to 2.5 per 1000 live births at the
end of the 1990s, but remains higher than the rate in normal
birthweight children. LBW children are also at greater risk of SIDS at
the end of the 1990s.
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References |
- Kitchen WH, Yu VYH, Lissenden JV, Bajuk B. Collaborative study of
very-low-birthweight infants: techniques of perinatal care and
mortality. Lancet 1982; 1: 1454-1457.
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Darlow BA, Horwood LJ, Mogridge N, Clemett RS. Prospective study of
New Zealand very low birthweight infants: outcome at 7-8 years. J
Paediatr Child Health 1997; 33: 47-51.
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Grether JK, Schulman J. Sudden infant death syndrome and birth
weight. J Pediatr 1989; 114: 561-567.
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Henderson-Smart DJ, Ponsonby AL, Murphy E. Reducing the risk of
sudden infant death syndrome: a review of the scientific literature.
J Paediatr Child Health 1998; 34: 213-219.
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The Consultative Council on Obstetric and Paediatric Mortality
and Morbidity. Annual Report for the Year 1993, incorporating the
32nd Survey of Perinatal Deaths in Victoria. Melbourne, 1994.
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The Consultative Council on Obstetric and Paediatric Mortality
and Morbidity. Annual Report for the Year 1994, incorporating the
33rd Survey of Perinatal Deaths in Victoria. Melbourne, 1995.
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The Consultative Council on Obstetric and Paediatric Mortality
and Morbidity. Annual Report for the Year 1995, incorporating the
34th Survey of Perinatal Deaths in Victoria. Melbourne, 1996.
-
The Consultative Council on Obstetric and Paediatric Mortality
and Morbidity. Annual Report for the Year 1996, incorporating the
35th Survey of Perinatal Deaths in Victoria. Melbourne, 1997.
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The Consultative Council on Obstetric and Paediatric Mortality
and Morbidity. Annual Report for the Year 1997, incorporating the
36th Survey of Perinatal Deaths in Victoria. Melbourne, 1998.
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Gardner MJ, Altman DG. Statistics with confidence - confidence
intervals and statistical guidelines. London: BMJ, 1989.
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Bigger HR, Silvestri JM, Shott S, Weese-Mayer DE. Influence of
increased survival in very low birth weight, low birth weight, and
normal birth weight infants on the incidence of sudden infant death
syndrome in the United States: 1985-1991. J Pediatr 1998;
133: 73-78.
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l'Hoir MP, Engelberts AC, van Well GT, et al. Case-control study of
current validity of previously described risk factors for SIDS in the
Netherlands. Arch Dis Child 1998; 79: 386-393.
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Malloy MH. Birth weight and gestational age specific sudden
infant death syndrome (SIDS) mortality: 1991 vs 1995. Pediatr
Res 1999; 45: 249A.
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Morley CJ, Thornton AJ, Cole TJ, et al. Baby Check: a scoring system
to grade the severity of acute systemic illness in babies under 6
months old. Arch Dis Child 1991; 66: 100-105.
-
Cole TJ, Gilbert RE, Fleming PJ, et al. Baby Check and the Avon
infant mortality study. Arch Dis Child 1991; 66: 1077-1078.
(Received 21 Jun, accepted 6 Sep, 1999)
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| | Authors' details |
Division of Paediatrics, Royal Women's Hospital, Melbourne, VIC.
Beverley Sowter, RN, Case Manager.
Lex W Doyle, MD, FRACP, Paediatrician; and Associate
Professor, Department of Obstetrics and Gynaecology, and
Department of Paediatrics, University of Melbourne.
Colin J Morley, MD, FRACP, Paediatrician.
Consultative Council on Obstetric and Paediatric Mortality and
Morbidity, Melbourne, VIC.
Anne Altmann, MB BS(Hons), MPH, FAFPHM, Epidemiologist.
Victorian Perinatal Data Collection Unit, Melbourne, VIC.
Jane Halliday, PhD, Epidemiologist.
Reprints will not be available from the authors.
Correspondence:
Associate Professor L W Doyle, Division of Paediatrics, The Royal
Women's Hospital, 132 Grattan Street, Carlton, VIC 3053.
l.doyleATobgyn-rwh.unimelb.edu.au
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Sudden unexpected deaths in early childhood in Victoria, 1993-1997 | | Birthweight subgroup
| | | 500-1499 g | 1500-2499 g | > 2499 g | Total |
| | Live births | 2781 | 15 630 | 297 617 | 316 028 | | Sudden unexpected deaths (≤ 28 days) | 0 | 7* | 16 | 23 | | Sudden unexpected deaths (> 28 days) | 7 | 24 | 170 | 201 | | Total sudden unexpected deaths | 7 | 31 | 186 | 224 | | Sudden unexpected deaths explained at autopsy | 0 | 0 | 10 | 10 | | Total SIDS | 7 | 31 | 176 | 214 | | Pathological features | | Definite | 5 | 8 | 61 | 74 | | Minor | 2 | 18 | 87 | 107 | | None | 0 | 5 | 28 | 33 | | Rate of SIDS (per 1000 livebirths) | 2.52 | 1.98 | 0.59 | 0.68 | | (95% CI) | (1.04-5.19) | (1.29-2.68) | (0.50-0.68) | (0.59-0.77) |
| | Data are numbers of infants, unless indicated otherwise.
* One infant died while still in hospital after birth.
SIDS = Sudden infant death syndrome (sudden unexpected deaths, excluding those explained at autopsy).
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