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Just over half (51%) of all births registered in 2008 were male babies, resulting in a sex ratio at birth of 105.5 male babies for every 100 female babies.
Nuptial and exnuptial births
In 2008, 66% of births were nuptial births; that is, births to parents who were married at the time of the birth (marriage in this publication refers to a registered marriage unless otherwise indicated). Exnuptial births accounted for the remaining 34% of births, although many of these births may have been to mothers in de facto relationships. The proportion of exnuptial births has been increasing since the 1950s, and has risen sharply over the last two decades.
Acknowledgment of paternity
With exnuptial births comes the possibility that the father may not acknowledge the birth (that is, the father has not signed the birth registration statement). While the number of exnuptial births has increased greatly over the past twenty years, the proportion of these births for which paternity was not acknowledged has decreased. In 1988 around 26% of all exnuptial births were paternity not acknowledged, but by 2008 this proportion had decreased to 9%. In terms of all births, paternity not acknowledged births have decreased from 5% of all births in 1988 to 3% in 2008.
Age of parents at confinement
The median age of all mothers of births registered in 2008 was 30.7 years. Women who registered an exnuptial birth in 2008 had a median age of 27.0 years, almost five years younger than women who registered a nuptial birth (31.9 years). The median age of women who registered an exnuptial birth where paternity was not acknowledged (25.5 years) was lower than the median age of women who registered an exnuptial birth where paternity was acknowledged (27.1 years).
Prior to the 1930s the median age of mothers giving birth had been decreasing. During the 1930s the median age stabilised, then rose briefly at the end of the Second World War, with an equally sharp decline immediately following the war. The median age of mothers fell substantially over the following three decades, reaching a low of 25.4 years in 1971. The reinterpretation of abortion law in New South Wales in 1971 was associated with a substantial fall in births to young women and an increase in the median age of mother. From 1972 onwards, the median age of mothers consistently increased, reaching 30.8 years in 2006, the highest on record.
However, data quality investigations during processing of 2007 birth registrations data indicated that age of parents, and therefore median age, may have been overstated for some birth registrations in 2006 and previous years (see paragraph 44 of the Explanatory Notes for more information). Despite the uncertainity associated with information on age of mother, the increases in median age of mother apparent since the early 1970s appear to have slowed or halted.
As age-specific fertility rates indicate, the median age of mothers is affected by current trends towards delayed childbearing, and repartnering and subsequent family formation following separation or divorce.
The median age of all fathers over the past two decades has also followed an upward trend. In 2008 the median age of all fathers was 33.1 years, with no change from 2006 and 2007. Data quality investigations during 2007 processing also indicated that age of parents, and therefore median age, may have been overstated for some birth registrations in 2006 and previous years.
Between 1988 and 2008 the median age of married fathers increased by almost three years, from 31.0 to 34.1 years, while the median age of unmarried fathers who acknowledged the birth of their child also increased, from 27.0 years to 29.8 years.
Number of previous children of the mother
Changes in ABS processing of data collected by state/territory Registrars of Births, Deaths and Marriages from 2007 have resulted in the availability of improved information on previous births to mothers.
Prior to 2007, ABS published information on previous births of the mother from the current relationship only, for all states and territories. From 2007, data on previous births for all relationships (both current and previous, if any) of the mother are collected for all states and territories, excluding Victoria and Queensland (see paragraphs 40 to 43 of the Explanatory Notes). Data for 2008 are presented in table 2.8. Due to high proportion of confinements in Tasmania for which no information on previous children of the mother was available, data for Tasmania has been excluded from analysis below.
Of the states and territories that collect data on all children born to a mother, the Australian Capital Territory recorded the highest proportion (44%) of first births of the mother (that is, no previous children), followed by Western Australia, New South Wales and South Australia (each 43%).
For mothers who registered a birth in 2008, the Australian Capital Territory and South Australia recorded the highest proportions (35% and 34% respectively) of mothers who had had one child previously, while the Northern Territory recorded the highest proportion (31%) of mothers with two or more previous children.
Graph 2.9 presents aggregate data for all states and territories excluding Queensland, Victoria and Tasmania. In 2008, 40% of nuptial confinements were to mothers with no previous children, 48% of exnuptial paternity acknowledged confinements were to mothers with no previous children, and 60% of exnuptial paternity not acknowledged confinements were to mothers with no previous children.
This pattern is reversed for mothers having their second or third child. In 2008, 36% of nuptial confinements were to mothers with one previous child, 28% of exnuptial paternity acknowledged confinements were to mothers with one previous child, and 18% of exnuptial paternity not acknowledged confinements were to mothers with one previous child.
Confinements resulting in a multiple birth
The number of confinements resulting in a multiple birth has increased consistently since the 1970s. In 2008, the number was 4,600, 24% more than the number recorded in 1988 (3,700 confinements) and 5% more than the number recorded in 2007 (4,400 confinements).