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4102.0 - Australian Social Trends, 2002  
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Contents >> Health >> Mortality and Morbidity: Infant mortality

Mortality and Morbidity: Infant mortality

Between 1900 and 2000, the rate of infant deaths decreased from 103 deaths per 1,000 live births to 5 deaths per 1,000 live births.

The survival of infants in their first year of life is commonly viewed as an indicator of the general health and wellbeing of a population. A low infant mortality rate is a major contributor to increased life expectancy. The improved survival of babies in Australia in the last century, as in many other developed countries, has been associated mainly with the decline of infectious diseases, along with growing preventative health measures and public health programs.1


Deaths among infants
The main source of data in this article is the ABS Deaths collection, compiled from data provided by the Registrar of Births, Deaths and Marriages in each State and Territory. For more information see Deaths, Australia, 2000 (ABS cat. no. 3302.0).

An infant death is the death of a child before its first birthday.

The infant mortality rate is the number of deaths in a calendar year of children aged under one year per 1,000 live births in the same calendar year. It comprises neonatal and postneonatal deaths.

A neonatal death is the death of an infant within 28 days (0-27) of birth who after delivery, breathed or showed any other evidence of life such as a heartbeat.

A postneonatal death is the death of an infant on or after 28 days but less than 12 months.

Perinatal conditions are diseases and conditions that originated during pregnancy or the neonatal period, even though death or morbidity may occur later.


Trends in infant mortality
Over the 20th century, the rate of infant deaths decreased from 103 deaths per 1,000 live births in 1900 to 5.2 deaths per 1,000 live births in 2000. The dramatic decline in the infant mortality rate during the first half of the century was linked to improvements in public sanitation and health education. In the 1940s, the development of vaccines and the ensuing programs of mass vaccination, along with effective use of antibiotics, resulted in further gains. These measures removed much of the earlier volatility in the infant mortality rate caused by outbreaks of infectious diseases. The more modest declines in the second half of the century were largely due to improved medical technology and education campaigns about the importance of immunisation;2 and most recently, in the case of Sudden Infant Death Syndrome (SIDS), infant sleeping position.3 Improvements in neonatal intensive care in the 1970s also played a major role in the continued decline in infant mortality in the latter part of the century.

Infant deaths are commonly divided into those which occur within the first 28 days of life (called the neonatal period) and those which occur on or after the 28th day but in the first year of life (called the postneonatal period). Improvements in infant mortality varied for babies of different age groups over the century. Until the 1940s, the decline in the infant mortality rate was mostly due to a rapid decline in postneonatal deaths. In contrast, after World War II, the decline was greater for neonatal deaths than for older babies.

Infant mortality rates are higher among boys than girls for almost all leading causes of death. This difference is largely biological in origin.4 Between 1980 and 2000, the infant mortality rate for boys was, on average, 27% higher than that for girls.

INFANT MORTALITY RATE(a)

(a) Per 1,000 live births.

Source: Deaths, Australia, 2000 (ABS cat. no. 3302.0).


Neonatal mortality
The death rate for babies aged under 28 days continued to decline rapidly over the last two decades of the 20th century. Between 1980 and 2000, the neonatal mortality rate declined from 7.1 to 3.5 deaths per 1,000 live births. The rate of decline was similar for boys and girls.

In 1997-2000, two major groups of causes accounted for 95% of neonatal deaths - conditions originating in the perinatal period (pregnancy and the first 28 days of life) (64%), and congenital malformations (31%). Conditions which originate in the perinatal period include causes that relate to pregnancy, fetal growth, labour and delivery. Congenital malformations are conditions present at birth that are either hereditary or originating from pregnancy, including deformities and chromosomal abnormalities.

NEONATAL DEATHS

1987-1990
1997-2000


Death rate(a)
Proportion of deaths
Death rate(a)
Proportion of deaths
Main cause of death
rate
%
rate
%

Certain conditions originating in the perinatal period
3.11
62.5
2.28
64.0
Congenital malformations, deformations and chromosomal abnormalities
1.61
32.4
1.09
30.5
Symptoms, signs and abnormal clinical and laboratory findings not elsewhere classified
0.11
2.3
0.06
1.8
Other causes
0.15
2.8
0.13
3.7
All causes
4.98
100.0
3.56
100.0

(a) Rate per 1,000 live births.

Source: ABS Causes of Death collection.


Over the last decade of the 20th century, the neonatal death rate from conditions originating in the perinatal period declined by 26%, from 3.1 deaths per 1,000 live births in 1987-1990 to 2.3 deaths per 1,000 live births in 1997-2000. In 1997-2000, 56% of neonatal deaths from conditions originating in the perinatal period were due to maternal factors and complications of pregnancy, labour and delivery (36% of all neonatal deaths). Because of changes in the classification of causes of death, a comparable figure is not available for 1987-1990. The two other common types of conditions originating in the perinatal period were hypoxia, birth asphyxia and other respiratory conditions (accounting for 12% of neonatal deaths in 1997-2000), and disorders relating to length of gestation and fetal growth (accounting for 4% of deaths). Both types of conditions made up a greater proportion of neonatal deaths a decade earlier (27% and 19% respectively in 1987-1990). Over the same period, there was a slight increase in the proportion of deaths from conditions which originate in the perinatal period which were not identified.

Between 1987-1990 and 1997-2000, the neonatal death rate for congenital malformations declined from 1.6 to 1.1 deaths per 1,000 live births, partly due to improved screening methods to detect such conditions (including amniocentesis and ultrasound) and greater awareness of preventative measures during pregnancy.

NEONATAL MORTALITY RATE(a)

(a) Rate per 1,000 live births.

Source: ABS Causes of Death collection.


Postneonatal mortality
Between 1980 and 2000, the mortality rate for babies aged 28 days and under one year declined by 53% from 3.6 to 1.7 deaths per 1,000 live births. The rate of decline was similar for boys and girls. Babies who die after the first 28 days of life were likely to die from a greater range of causes than those who die in their first four weeks of life. Congenital malformations and conditions originating in the perinatal period were again among the more common causes of postneonatal deaths, accounting for 21% and 12% of deaths respectively in 1997-2000. However, the most commonly cited group of causes were symptoms, signs and abnormal clinical and laboratory findings not elsewhere classified. This group of causes accounted for a third of postneonatal deaths in 1997-2000, the bulk of them (30% of all postneonatal deaths) caused by Sudden Infant Death Syndrome (SIDS).


Causes of infant deaths
Infant deaths are classified according to the International Classification of Diseases (ICD). There have been a number of revisions of the ICD, the most recent being the ICD-10 introduced to Australian deaths statistics in 1999.

Deaths which occurred prior to 1999 have been matched with the ICD-10 codes to facilitate comparison over time. This article discusses infant deaths classified to the following categories of underlying causes of death in the ICD-10 (followed by the equivalent ICD-9 code):
  • certain infectious and parasitic diseases, A00-B99 (001-139);
  • diseases of the nervous system, G00-G99 (320-389);
  • diseases of the respiratory system, J00-J99 (460-519);
  • certain conditions originating in the perinatal period, P00-P96 (760-779);
  • congenital malformations, deformations and chromosomal abnormalities, Q00-Q99 (740-759);
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified, R00-R99 (780-799); and
  • external causes of morbidity and mortality, V01-Y98 (E800-E899).


Between 1987-1990 and 1997-2000, the postneonatal death rate for SIDS declined from 1.8 to 0.5 deaths per 1,000 live births. Proportionally, this equated to a decrease from 54% to 30% of all postneonatal deaths. The decrease in death rate for SIDS occurred following the introduction of a national health educational campaign in 1990. The campaign highlighted the risk factors which are associated with SIDS such as sleeping position, feeding practices and exposure to passive smoking.3

POSTNEONATAL DEATHS

1987-1990
1997-2000


Death rate(a)
Proportion of deaths
Death rate(a)
Proportion of deaths
Main cause of death
rate
%
rate
%

Certain infectious and parasitic diseases
0.08
2.2
0.06
3.2
Diseases of the nervous system
0.13
3.9
0.11
6.5
Diseases of the respiratory system
0.17
5.0
0.09
5.1
Certain conditions originating in the perinatal period
0.31
9.2
0.21
12.1
Congenital malformations, deformations and chromosomal abnormalities
0.55
16.1
0.37
21.1
Symptoms, signs and abnormal clinical and laboratory findings not elsewhere classified
1.85
54.5
0.57
32.8
Sudden infant death syndrome
1.83
54.0
0.51
29.7
External causes of morbidity and mortality
0.18
5.2
0.16
9.2
Other causes
0.13
3.9
0.17
10.0
All causes
3.39
100.0
1.73
100.0

(a) Rate per 1,000 live births.

Source: ABS Causes of Deaths Collection.


The death rates for conditions originating in the perinatal period, and for congenital malformations declined to 0.2 and 0.4 deaths per 1,000 live births respectively between 1987-1990 and 1997-2000. However, these two groups of causes accounted for a greater proportion of postneonatal deaths in 1997-2000 than they did a decade earlier, as a result of the greater gains in reducing deaths caused by SIDS and the improved survival of babies with these conditions beyond the first 28 days of life.

POSTNEONATAL MORTALITY RATE(a)

(a) Rate per 1,000 live births.

Source: ABS Causes of Death collection.


State and Territory differences
There is some variation in infant mortality rates across States and Territories. In 2000, the rates ranged from 4.2 deaths per 1,000 live births in the ACT to 11.7 deaths per 1,000 live births in the Northern Territory. The notably higher infant mortality rate in the Northern Territory reflects the higher proportion of Indigenous babies born in the Northern Territory. Overall, the infant mortality rate for the Indigenous population is much higher than for the total Australian population (13.5 deaths per 1,000 live births compared with 5.3 deaths per 1,000 live births in 1998-2000). For more information on Indigenous mortality rates see Australian Social Trends 2002, Mortality of Aboriginal and Torres Strait Islander peoples.

STATE/TERRITORY INFANT MORTALITY RATES(a)

State/Territory
1980
1990
2000

NSW
10.9
8.1
5.2
Vic.
10.0
7.8
4.5
Qld
10.9
7.7
6.2
SA
10.1
8.5
4.6
WA
11.7
8.6
4.3
Tas.
12.8
8.9
5.8
NT
14.2
15.2
11.7
ACT
8.0
9.4
4.2
Aust.
10.7
8.2
5.2

(a) Rate per 1,000 live births.

Source: Deaths, Australia, 2000 (ABS Cat. no. 3302.0).


Between 1980 and 2000, the infant mortality rate for Australia decreased by 51%, from 10.7 to 5.2 deaths per 1,000 live births. Decreases varied across States and Territories with Western Australia and Victoria experiencing the greatest declines over the period - 63% and 55% to 4.3 and 4.5 deaths per 1,000 live births respectively in 2000. While infant mortality rates in Tasmania and the Australian Capital Territory have decreased in line with the national trend, they have shown more variability from year to year due to the small numbers of infant deaths.


INTERNATIONAL COMPARISON
Despite continued declines in the infant mortality rates of most countries over the last 20 years, there continues to be a wide variation in the rates experienced in different countries. Australia's infant mortality rate is among the lowest in the world.

SELECTED INFANT MORTALITY RATES(a)

1978
1998

Hong Kong, SAR of China
11.8
3.2
Japan
8.4
3.6
Sweden
7.8
(c)3.7
Singapore
12.6
4.2
Australia
12.2
5.0
Canada
12.0
(c)5.3
New Zealand
13.8
5.3
Italy
17.1
(c)5.5
United Kingdom
13.3
(c)5.9
Greece
19.3
6.1
United States of America
13.8
7.2
Korea, Republic of
(b)36.7
(d)10.0
Viet Nam
(b)106.4
(d)38.2
China
(e)48.7
(f)41.0
Indonesia
(b)98.7
(d)48.4
Papua New Guinea
(b)110.9
(d)61.4

(a) Rate per 1,000 live births.
(b) Estimate for 1975-80.
(c) 1997 data.
(d) Estimate for 1995-2000.
(e) 1979 data.
(f) 1995 data.

Source: United Nations, Demographic Yearbook 1998; and Demographic Yearbook 1982.


Endnotes
1 United Nations, 1988 Mortality of children under age 5: World Estimates and projections 1950-2025, United Nations, New York.

2 Stanley, F. J. 2001, 'Child health since Federation', in Year Book Australia 2001, ABS cat. no. 1301.0, pp. 368-400, Ausinfo, Canberra.

3 SIDS Australia Online, <URL: http://www. sidsaustralia.org.au/> (accessed 25/10/2001).

4 Australian Bureau of Statistics 1998, Causes of Infant and Child Deaths, 1982-1996, cat. no. 4398.0, ABS, Canberra.



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