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TRENDS IN NATIONAL FERTILITY RATES
Care should be exercised in interpreting trends over time in the 'period' TFR as presented in this publication. While the TFR is widely used as a summary measure of a population's current and historical fertility trends, it does not reflect tempo changes in fertility. Tempo changes are the effect of successive cohorts of women who delay or forego having children only to catch up in subsequent years. Analysis of age-specific fertility rates and parity assists in understanding tempo effects in fertility over time.
Age-specific fertility rates
Consistent with the overall increase in Australia's TFR, age-specific fertility rates for all age groups of mother increased between 2007 and 2008, except for women aged 45-49 years, for whom the fertility rate remained the same. The increase in the TFR between 2007 and 2008 was largely due to births to women aged 30 to 39 years, who accounted for 55% of the increase. Births to women aged 15 to 29 years accounted for 31% of the increase in the TFR.
Over the past few decades, the decline in Australia's TFR has been associated with the tendency for women to have their babies at older ages. The median age of all women who gave birth in 1998 was 29.5 years; by 2006 this had increased to 30.8 years and has remained at a similar level since then (30.7 years in 2008) (see graph 2.7).
The transition to an older age-specific fertility pattern is illustrated by the shift in peak fertility rates, from women aged 25-29 years in 1999 to women aged 30-34 years in 2000. Since then, women aged 30-34 years have continued to record the highest fertility rate of all age groups, with 127.8 babies per 1,000 women in 2008.
Women aged 25-29 years experienced the second highest fertility rate in 2008, with 105.8 babies per 1,000 women, while women aged 35-39 years and 20-24 years experienced fertility rates of 70.9 and 57.1 babies per 1,000 women respectively.
Until the late 1970s the distribution of fertility rates across age groups was relatively stable, with each age group peaking and troughing together, although some peaks were more pronounced for some age groups than others (graph 2.2). Women aged 25-29 years had the highest fertility rates for most of this period, followed by women aged 20-24 years. Increasing fertility rates since the mid 1970s amongst women aged 30-34 years resulted in the fertility rate for this age group exceeding that of women aged 20-24 years in 1987 and that of women aged 25-29 years in 2000. In 2004 the fertility rate for women aged 35-39 years exceeded that of women aged 20-24 years for the first time, with this trend continuing since then.
Fertility rates amongst younger women have followed a declining trend over the past two to three decades, however in recent years this trend appears to have halted, with increases in rates being recorded since 2006. Women aged 20-24 years experienced the greatest overall decrease, with the fertility rate halving between 1980 and 2006 (from 107.0 babies per 1,000 women to 51.4 babies per 1,000 women in 2006), but increasing to 57.1 babies per 1,000 women by 2008. Fertility rates for women aged 25-29 years decreased by 28% between 1980 and 2006 (from 141.0 babies per 1,000 women to 101.0 babies per 1,000 women) but increased to 105.8 babies per 1,000 women in 2008. The teenage fertility rate (births to women aged 15-19 years) decreased by 44% between 1980 and 2006 (from 27.6 babies per 1,000 women to 15.3 babies per 1,000 women) and has since risen to 17.3 babies per 1,000 women.
Fertility rates for the older age groups have consistently increased between 1980 and 2008. The fertility rate for women aged 30-34 years increased by 70% (from 75.1 babies per 1,000 women in 1980 to 127.8 babies per 1,000 women in 2008) while the rate for women aged 35-39 years tripled (from 23.7 babies per 1,000 women to 70.9 babies per 1,000 women). The fertility rate for women aged 40-44 years more than tripled over this period, from 4.4 babies per 1,000 women to 14.1 babies per 1,000 women, as the trend towards older motherhood continued.
Since 1976 Australia has experienced total fertility rates below replacement level. That is, the average number of babies born to a woman throughout her reproductive life (the TFR) has been insufficient to replace herself and her partner. Although the TFR required for replacement is currently around 2.1 babies per woman, this number is not constant. Because the level of fertility required for replacement is dependent on the number of women who survive to reproductive ages, replacement fertility has declined in parallel with decreases in female mortality. In 1921, when mortality rates were high, replacement fertility was 2.4 babies per woman. By 1954, it had decreased to 2.1, and by 1996 replacement fertility was 2.08. Even if female mortality declined to zero for women up to the end of their reproductive lives, the replacement level would still be 2.05 (1.05 male and 1.0 female babies) - higher than the 2008 TFR of 1.97 babies per woman.
Completed fertility refers to the number of children that a woman born in a particular year has had by the end of her reproductive life. A limitation of this measure of fertility is that it cannot be observed until a woman's reproductive life is complete. To overcome this limitation, a measure of completed fertility based on observed and assumed age-specific fertility rates is used in table 2.3.
Completed fertility rates of women born in the early 1930s are the highest on record in Australia (3.1 children). These women were the mothers of the 'baby boom' generation. Since then, completed fertility has declined, while the median age of mothers has increased. The 2006 to 2101 issue of Population Projections, Australia (cat. no. 3222.0, Series B) assumed completed fertility of women born in 2008 to be 1.8 births per woman.
For more information on completed fertility derived from the 2006 Census, see Chapter 5: How Many Children Do Australian Women Have? of the 2006 issue of Births, Australia (cat. no. 3301.0) .