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Births and pregnancy outcome

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Births and pregnancy outcome

In 2011, there were 2,506 births registered in WA (1,291 males and 1,215 females) with one or both parents identified as Indigenous (7.8% of all births registered) [1]. (Implied coverage of Indigenous births in WA for 2002-2006 was estimated at 95% based on 2001 Census-based projections). Both parents were identified as Indigenous in 44% of the births. Only the mother identified as Indigenous in 35% of Indigenous registered births (including births where paternity was not acknowledged and those where the father’s Indigenous status was unknown), and only the father identified as Indigenous in 21% (including births where the mother’s Indigenous status was unknown).

Box 1: About births and fertility

In Australia, all births are required by law to be registered with the registrar of the state/territory in which the birth occurred. Because the information collected through the registration process is quite limited from a health perspective, the health authorities established parallel collections. These maternal/perinatal collections, which are based on data recorded by midwives and other staff attending births, collect information about the nature, duration, and complications of the pregnancy, labour, and puerperium periods, as well as 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). This section draws on the information collated by these two agencies.

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 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 born to 1,000 women at the current age-specific patterns of fertility.

Age of mothers

In 2011, Indigenous women in WA tended to have more babies and to have them at younger ages than did non-Indigenous women [1]. The median age of Indigenous mothers was 24.2 years compared with 30.3 years for all mothers. In 2011, the highest age-specific fertility rates were for the 20-24 years age-group for Indigenous women and in the 30-34 years age-group for all women (Table 2). The fertility rate of Western Australian teenage Indigenous women (106 babies per 1,000 women) was more than five times that for all teenage women in WA.

Table 2: Age-specific fertility rates, by Indigenous status of mother, WA and Australia, 2011
Age-group (years)Western AustraliaAustralia
Indigenous mothersAll mothersIndigenous mothersAll mothers
Source: ABS, 2012 [1]
Notes:
  1. Rates are births per 1,000 women in each age-group
  2. n.p. refers to numbers not available for publication, but included in totals where applicable
  3. Births to mothers aged less than 15 years are included in the 15-19 years age-group
  4. Births to mothers aged 50 years or older are included in the 45-49 years age-group
15-19 106 19 78 16
20-24 180 58 155 52
25-29 154 107 147 101
30-34 101 125 105 122
35-39 52 66 52 70
40-44 n.p. 15 11 15
45-49 n.p. 0.8 0.6 0.8

Total fertility rates

In 2011, the total fertility rate for Indigenous women living in WA was 3,011 births per 1,000 compared with 1,953 per 1,000 for all Western Australian women [1]. WA had the highest total fertility rate for Indigenous women, followed by Qld (2,932 per 1,000) and NSW (2,683 per 1,000). The total fertility rate for Indigenous women in Australia was 2,740 births per 1,000 compared with 1,884 births per 1,000 for all Australian women.

Method of birth

In 2010, Indigenous mothers in WA were more likely than non-Indigenous mothers to have a non-instrumental vaginal (including breech) birth (68% compared with 51%) and less likely to have assisted instrumental vaginal deliveries (forceps or vacuum extraction) (7.7% compared with 15%) [2]. Indigenous mothers in WA also had a lower proportion of births by caesarean section than non-Indigenous mothers (25% compared with 34%).

Birthweights

In 2010, the average weight of babies born to Indigenous mothers living in WA was 3,139 grams, which was 214 grams lighter than the average for babies born to all Western Australian mothers (3,353 grams) [2]. Babies born to Indigenous women in WA were more than twice as likely to be of low birthweight (LBW) than were those born to all women in WA (13.6% compared with 6.1%). (LBW, defined as a birthweight of less than 2,500 grams, increases the risk of illness and death in infancy and of other health problems.)

Risk factors for LBW include socioeconomic disadvantage, the size and age of the mother, the number of babies previously born, the mother’s nutritional status, illness during pregnancy, the duration of the pregnancy, and mother’s alcohol consumption and use of tobacco and other drugs during pregnancy [2][3]. According to the WAACHS, infants born to mothers who used tobacco during pregnancy had a significantly lower average birth weight (3,110 grams) than did infants born to mothers who had not used tobacco during pregnancy (3,310 grams) [4]. Lowest average birthweights were for infants whose mothers used marijuana with tobacco (3,000 grams) or with both tobacco and alcohol (2,940 grams).

References

  1. Australian Bureau of Statistics (2012) Births, Australia, 2011. Canberra: Australian Bureau of Statistics
  2. Li Z, Zeki R, Hilder L, Sullivan EA (2012) Australia's mothers and babies 2010. Canberra: Australian Institute of Health and Welfare
  3. 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
  4. 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
 
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