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Births and pregnancy outcome

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Births and pregnancy outcome

In 2012, there were 18,295 births registered in Australia with one or both parents identified as Indigenous (6% of all births registered) [1]. This number probably underestimates the true number slightly as Indigenous status is not always identified, and there may be a lag in birth registrations. The ABS estimates that 96% of Indigenous births in 2002-2006 were correctly identified as such [2]. Completeness of identification varied across the country, with only Vic, Qld, WA, South Australia (SA) and the NT having levels above 90%.

In 2012, both parents identified as Indigenous in 30% of those registered as Indigenous, only the mother in 42% (including births where paternity was not acknowledged and those where the father's Indigenous status was unknown), and only the father in 28% (including births where the mother's Indigenous status was unknown) [1].

Box 1: About births and fertility

In Australia, all births are required by law to be registered with the Registrar of Births, Deaths and Marriages in the state/territory in which the birth occurred. The information collected through registration is limited from a health perspective, so health authorities have established parallel maternal/perinatal collections. These collections are based on data recorded by midwives and other staff attending births and include information about the nature, duration, and complications of the pregnancy, labour, and puerperium periods, and details about the baby (including weight, length, condition at birth, and complications). Information from the two collections is collated and reported nationally ΜΆ by the ABS (for registration information) and the AIHW’s National Perinatal Statistics Unit (for maternal/perinatal information).

The study of birth information is known as fertility analysis, where ‘fertility’ refers to the number of babies born alive. This meaning is different to the lay use of the word, which means the capacity to bear children. The technical term for the capacity to bear children is ‘fecundity’.

The actual numbers of births are of limited use for public health purposes. To be useful, the actual numbers of births must be related to the population in which they occur. There are a number of general measures of births and fertility, but detailed analysis involves the use of age-specific rates. These rates are the annual number of births per 1,000 women in five-year age-groups from 15 to 44 years. (The relatively small numbers of births to women aged less than 15 years are included in the 15-19 years age-group, and those older than 44 years in the 40-44 years age-group.) The summary measure of fertility is the total fertility rate, which is the sum of age-specific fertility rates multiplied by five (since five-year age-groups are involved). It estimates the number of children that would be born to 1,000 women if each woman experienced current age-specific fertility rates at each age of her reproductive life.

Age of mothers

In 2012, Indigenous women had more babies and had them at younger ages than did non-Indigenous women – teenagers had one-fifth (19%) of the babies born to Indigenous women, compared with only 3.7% of those born to all mothers [1]. The median age of Indigenous mothers was 24.8 years, compared with 30.7 years for all mothers. The highest birth rates (known technically as fertility rates) were for the 20-24 years age-group for Indigenous women and for the 30-34 years age-group for all women (Table 1). The fertility rate of teenage Indigenous women (79 babies per 1,000 women) was almost five times that of all teenage women (16 babies per 1,000).

Table 1: Age-specific fertility rates, by Indigenous status of mother, selected jurisdictions, Australia, 2012
Status of mother/age-group (years)Jurisdiction
NSWVicQldWASANTAustralia
Source: ABS, 2013 [1]
Notes:
  1. Rates per 1,000 women in each age-group; the 15-19 years age-group includes births to women aged 14 years or younger, and the 40-44 years age-group includes births to women aged 45 years or older
  2. Figures are not provided for Tas and the ACT because of the small numbers involved and doubts about the level of identification of Indigenous births, but numbers for these jurisdictions are included in figures for Australia
Indigenous mothers
15-19 67 68 84 106 68 90 79
20-24 149 133 165 170 138 137 151
25-29 143 143 159 161 133 113 144
30-34 106 105 112 114 89 77 103
35-39 49 65 56 56 49 37 52
40-44 14 12 14 14 6.3 10 13
All mothers
15-19 14 11 22 19 16 51 16
20-24 52 42 66 57 52 99 53
25-29 102 96 112 102 108 106 103
30-34 127 133 123 124 124 112 127
35-39 74 80 63 67 65 58 72
40-44 17 17 13 14 13 15 15

Total fertility rates

In 2012, total fertility rates were 2,710 births per 1,000 for Indigenous women and 1,933 per 1,000 for all women (Table 2) [1]. The highest total fertility rate for Indigenous women was for WA (3,103 babies per 1,000 women), followed by Qld (2,953 per 1,000) and NSW (2,652 per 1,000).

Table 2: Total fertility rates, by Indigenous status of mother, selected jurisdictions, Australia, 2012
Status of motherJurisdiction
NSWVicQldWASANTAustralia
Source: ABS, 2013 [1]
Notes:
  1. Total fertility rate is the number of children born to 1,000 women at the current level and age pattern of fertility (see Box 1)
  2. Figures are not provided for Tas and the ACT because of the small numbers involved and doubts about the level of identification of Indigenous births. Numbers for those jurisdictions are included in figures for Australia
Indigenous 2,652 2,635 2,953 3,103 2,411 2,322 2,710
All mothers 1,932 1,891 1,997 1,913 1,898 2,206 1,933

Birthweights

The average weight of babies born to Indigenous mothers in 2011 was 3,187 grams, 187 grams less than the average for babies born to non-Indigenous mothers (3,375 grams) [3]. Babies born to Indigenous women in 2011 were more than twice as likely to be of low birthweight (LBW) (12.6%) than were those born to non-Indigenous women (6.0%). (LBW, defined as a birthweight of less than 2,500 grams, increases the risk of death in infancy and other health problems.)

The proportions of LBW babies born to Indigenous women were highest in the ACT (27%)1, the NT (16%), and SA (15%) [3]. The proportions of babies of LBW were higher for Indigenous mothers than for all mothers in all jurisdictions (Table 3).

Table 3: Mean birthweights and percentage of low birthweight for babies born to Indigenous and all mothers, selected jurisdictions, Australia, 2011
 NSWVicQldWASATasACTNTAustralia
Source: Li, Zeki, Hilder, Sullivan, 2013 [3]
Notes:
  1. LBW is defined as less than 2,500 grams
Indigenous mothers
Mean birthweight 3,229 3,246 3,215 3,144 3,116 3,206 2,929 3,089 3,187
% low birthweight 11.6 12.6 11.2 13.0 15.2 13.2 27.2 15.6 12.6
All mothers
Mean birthweight 3,372 3,371 3,377 3,355 3,340 3,381 3,343 3,275 3,367
% low birthweight 5.8 6.3 6.4 6.0 6.9 7.6 8.1 9.6 6.3

Risk factors for LBW include socioeconomic disadvantage, the size and age of the mother, the mother's nutritional status, illness and stress during pregnancy, and domestic violence [4]. A mother's alcohol consumption and use of tobacco and other drugs during pregnancy also impact on the birthweight of her baby. Tobacco, in particular, has a major impact on birthweight. In 2011, one-half (50%) of Indigenous mothers and 12% of non-Indigenous mothers reported smoking during pregnancy [3].

The impact of tobacco smoking during pregnancy can be seen in the proportions of LBW babies; in 2009, the proportion of LBW babies was twice as high among Indigenous mothers who smoked during pregnancy (15%) than among those who did not smoke during pregnancy (7.6%) [5]. Similarly, 10% of babies born to non-Indigenous mothers who smoked were of LBW, compared with less than 5% of those whose mothers did not smoke.

The mean birthweight of live babies born in 2001-2004 to Indigenous women who used tobacco was 3,037 grams, 253 grams lighter than those born to Indigenous women who did not use tobacco (3,290 grams) [6]. The comparable figures for live babies born to non-Indigenous women were 3,210 grams for women who smoked and 3,416 grams for women who did not smoke.

The 2000-2001 Western Australian Aboriginal child health survey (WAACHS) reported slightly higher average birthweights than the weights documented above – 3,110 grams for babies born to Indigenous mothers who used tobacco in pregnancy and 3,310 grams for those whose Indigenous mothers did not [7]. The lowest average birthweights reported in the WAACHS were for babies whose Indigenous mothers used marijuana with tobacco (3,000 grams), and marijuana with both tobacco and alcohol (2,940 grams).

References

  1. Australian Bureau of Statistics (2013) Births, Australia, 2012. Canberra: Australian Bureau of Statistics
  2. Australian Bureau of Statistics (2007) Births, Australia, 2006. Canberra: Australian Bureau of Statistics
  3. Li Z, Zeki R, Hilder L, Sullivan EA (2013) Australia's mothers and babies 2011. Canberra: Australian Institute of Health and Welfare
  4. Ashdown-Lambert JR (2005) A review of low birth weight: predictors, precursors and morbidity outcomes. Journal of the Royal Society for the Promotion of Health; 125(2): 76-83
  5. Australian Institute of Health and Welfare (2013) Aboriginal and Torres Strait Islander health performance framework 2012: detailed analyses. Canberra: Australian Institute of Health and Welfare
  6. Leeds K, Gourley M, Laws P, Zhang J, Al-Yaman F, Sullivan EA (2007) Indigenous mothers and their babies, Australia 2001-2004. Canberra: Australian Institute of Health and Welfare
  7. Zubrick SR, Lawrence DM, Silburn SR, Blair E, Milroy H, Wilkes T, Eades S, D'Antoine H, Read AW, Ishiguchi P, Doyle S (2004) The health of Aboriginal children and young people [volumes 1-4]. Perth: Telethon Institute for Child Health Research

Endnotes

  1. Information about LBW babies in the ACT includes information of non-ACT residents (28% of Indigenous women who gave birth in the ACT were non-residents). In 2011, 16% of babies born to Indigenous women who were ACT residents were of LBW.
 
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