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Infant Mortality
Introduction
Infant mortality is often used as a barometer of the social wellbeing of a country [1]. New New Zealand’s infant mortality rates are middling by international standards, being lower than those of the USA and some Eastern European countries, but higher than those of Central and Northern Europe [2]. Despite this, mortality during the first year of life in New Zealand remains much higher than at any other point during childhood or adolescence. During 2009, a total of 308 New Zealand infants were registered as dying prior to their first birthday [3].
Despite these relatively high numbers, New Zealand’s infant mortality rates have declined during the past 40 years, with rates falling from 16.9 per 1,000 in 1969, to 4.9 per 1,000 in March 2009 [3]. While infant mortality rates are generally higher for Pacific > Māori > European / Other babies, males, and those in the most deprived areas [4], total infant mortality rates are of limited utility in guiding population health interventions, as the causes of mortality differ markedly with the age of the infant. During the neonatal period (birth–28 days) extreme prematurity, congenital anomalies and intrauterine / birth asphyxia are the leading causes of mortality, while in the post neonatal period (29–364 days) sudden unexpected death in infancy (SUDI) and congenital anomalies make the greatest contribution [5]. Thus any interventions aimed at reducing New Zealand’s infant mortality rates must, in the first instance, be based on an understanding of their component causes.
The following section uses information from the National Mortality Collection to review neonatal, post neonatal and total infant mortality since 1990.
Data Source and Methods
Definition
1. Total Infant Mortality: Death of a live born infant prior to 365 days of life
2. Neonatal Mortality: Death of a live born infant in the first 28 days of life
3. Post-Neonatal Mortality: Death of a live born infant after 28 days but prior to 365 days of life
4. Sudden Unexpected Death in Infancy (SUDI): Death of a live born infant < 365 days of life, where the cause of death is attributed to SIDS, Accidental Suffocation / Strangulation in Bed or Ill-Defined/Unspecified Causes
Data Source
Numerator: Sources Numerator: National Mortality Collection: All deaths in the first year of life, using the definitions for total infant, neonatal and post neonatal mortality outlined above. Cause of death was derived from the main underlying cause of death as follows: Extreme Prematurity (ICD-10 P072), Congenital Anomalies (ICD-10 Q00–Q99), Perinatal Conditions (ICD-10 P00–P96); SIDS (ICD-10 R95); SUDI (ICD-10 R95, R96, R98, R99, W75).
Denominator: Birth Registration Dataset: All live births 20+ weeks gestation.
Notes on Interpretation
Note 1: See Appendix 3 for an overview of the dataset used.
Note 2: 95% confidence intervals have been provided for the rate ratios in this section and where appropriate, the terms significant or not significant have been used to communicate the significance of the observed associations. Tests of statistical significance have not been applied to other data in this section, and thus (unless the terms significant or non-significant are specifically used) the associations described do not imply statistical significance or non-significance (see Appendix 1 for further discussion of this issue).
New Zealand Distribution and Trends
New Zealand Trends
In New Zealand during 1990–2008, neonatal and post neonatal mortality both declined, with neonatal mortality exceeding post neonatal mortality during 1996–2008 (Figure 1).
New Zealand Trends by Ethnicity
In New Zealand during the late 1990s, neonatal mortality was generally higher for Pacific and Māori > European > Asian infants, although ethnic differences were less consistent during the 2000s. In contrast, post neonatal mortality was higher for Māori > Pacific > European and Asian infants throughout 1996–2008 (Figure 2).
Figure 1. Total Infant, Neonatal and Post Neonatal Mortality, New Zealand 1990–2008
Source: Numerator National Mortality Collection; Denominator Birth Registration Dataset
Figure 2. Total Infant, Neonatal and Post Neonatal Mortality by Ethnicity, New Zealand
1996–2008
Source: Numerator: National Mortality Collection; Denominator: Birth Registration Dataset. Ethnicity is Level 1 Prioritised
Distribution by Cause
In New Zealand during 2004–2008, extreme prematurity and congenital anomalies were the leading causes of neonatal mortality, although intrauterine / birth asphyxia and other perinatal conditions also made a significant contribution. In contrast, SUDI was the leading cause of post neonatal mortality, followed by congenital anomalies (Table 1).
Table 1. Neonatal and Post Neonatal Mortality by Cause, New Zealand 2004–2008
Source: Numerator National Mortality Collection; Denominator Birth Registration Dataset
Distribution by Ethnicity, Gender, NZDep Deprivation, Maternal Age and Gestation
Neonatal Mortality: In New Zealand during 2004–2008, neonatal mortality was significantly higher for Pacific and Māori infants than for European infants, for males, those in average / more deprived (NZDep decile 5–10) areas, preterm infants, and those whose mothers were <25 years of age (Table 2, Figure 3).
Post Neonatal Mortality: In New Zealand during 2004–2008, post neonatal mortality was also significantly higher for Māori and Pacific infants than for European and Asian infants, for males, those in average / more deprived (NZDep decile 5–10) areas, preterm infants, and those whose mothers were <30 years of age (Table 2, Figure 3).
Table 2. Risk Factors for Neonatal and Post Neonatal Mortality, and Sudden Unexpected Death in Infancy (SUDI), New Zealand 2004–2008
Source: Numerator National Mortality Collection; Denominator Birth Registration Dataset; Rates are per 100,000, Rate Ratios are Unadjusted, Ethnicity is Level 1 Prioritised. SUDI is neonatal AND post neonatal.
Figure 3. Distribution of Neonatal and Post Neonatal Mortality, and Sudden Unexpected Death in Infancy (SUDI) by NZ Deprivation Index Decile, New Zealand 2004–2008
Source: Numerator: National Mortality Collection; Denominator: Birth Registration Dataset. Note: SUDI is neonatal AND post neonatal; Decile is NZDep2001
SUDI: In New Zealand during 2004–2008, mortality from SUDI was significantly higher for Māori > Pacific > European > Asian infants, those in average / more deprived (NZDep decile 3–10) areas, preterm infants, and those whose mothers were <30 years of age (Table 2, Figure 3).
Summary
In New Zealand during 1990–2008, neonatal and post neonatal mortality both declined, with neonatal mortality exceeding post neonatal mortality during 1996–2008. When broken down by ethnicity, neonatal mortality was higher for Pacific and Māori > European > Asian infants during the late 1990s, although ethnic differences were less consistent during the 2000s. In contrast, post neonatal mortality was higher for Māori > Pacific > European and Asian infants throughout 1996–2008.
During 2004–2008, neonatal and post neonatal mortality were also significantly higher for Pacific and Māori infants, males, those in average / more deprived areas, preterm infants and those with younger mothers. Similarly mortality from SUDI was significantly higher for Māori > Pacific > European > Asian infants, those in average / more deprived areas, preterm infants, and those whose mothers were <30 years of age.
References
1. Gorski P. 1998. Perinatal Outcome and Social the Contract - Interrelationships Between Health and Humanity. Journal of Perinatology 18(4) 297 - 301.
2. OECD Social Policy Division. 2008. OECD Family Database: CO1 Infant Mortality. OECD Health at a Glance 2008
http://www.oecd.org/document/4/0,3343,en_2649_34819_37836996_1_1_1_1,00.html
3. Statistics New Zealand. 2011. Demographic Trends: 2010 Deaths and Life Expectancy. Wellington: Statistics New Zealand.
4. Public Health Intelligence. 2004. An Indication of New Zealander's Health 2004. Wellington: Ministry of Health.
5. Craig E, Jackson C, Han D, et al. 2007. Monitoring the Health of New Zealand Children and Young People: Indicator Handbook. Auckland: Paediatric Society of New Zealand & New Zealand Child and Youth Epidemiology Service.