Stillbirths in Australia 1991-2009

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Australia is considered to be one of the safest countries in which to give birth. Viewed against comparable statistics worldwide, the rate of stillbirth in Australia is among the lowest in the world. Yet 1 baby for every 135 born in this country is a stillbirth. The definition of a ‘stillbirth’ varies internationally. A ‘stillbirth’ in Australia is defined as the birth of a baby who shows no signs of life, after a pregnancy of at least 20 weeks gestation or weighing 400g or more.

This first Australian report of stillbirths examines the association of maternal, pregnancy and birth factors with stillbirth. The report makes use of the extensive data about pregnancy and birth that have been collected in all states and territories since 1991. For the period 1991–2009, the stillbirth rate ranged from 6.4–7.8 per 1,000 births, with no discernable trend. In 2009, the stillbirth rate was 7.8 per 1,000 births. In contrast, over these years there has been a continuing slow decline in neonatal mortality from 3.8–2.8 per 1,000 live births.

However, there have been changes over time in the stillbirth rate within subgroups of women with different characteristics. Between 1991 and 2009, the stillbirth rates in mothers aged 40 or older fell from 12.7 to 10.6 per 1,000 births, but rose in teenage mothers from 9.5 to 15.0 per 1,000 births. The increasing rate of stillbirth among younger women warrants further investigation. Among Aboriginal and Torres Strait Islander mothers, stillbirth rates fell from 15.5 per 1,000 total births in 1991–94 to 12.3 per 1,000 total births in 2005–09, while stillbirth rates among babies born to non-Indigenous mothers rose from 6.6 to 7.2 per 1,000 total births. Similarly falling rates of stillbirth over time among babies with higher birthweights were offset by increasing rates among babies with low birthweight; falling rates of stillbirth among twins were offset by increasing rates among singletons and higher order multiple births.

Information about the causes of stillbirth from 2004–08 was provided from state and territory committees where a review of perinatal deaths was undertaken and each death classified to the Perinatal Society of Australia and New Zealand (PSANZ) Perinatal Death Classification. The most common specified cause of stillbirth in Australia was congenital anomaly, accounting for 21% of all stillbirths. However as a group, the PSANZ category for unexplained antepartum stillbirths was slightly more common, accounting for 22% of
stillbirths. The number of antepartum stillbirths of unknown cause aligns with findings elsewhere, but must be viewed cautiously because of the low rates of autopsy, which was 38.1% overall, and the lack of available data on placental post-mortem examinations.

Since 1991 there have been progressive increases in the risk of stillbirth from 20–23 weeks gestational age. Most of these deaths were due to congenital anomaly and this increase coincides with the expansion of screening programs for fetal anomaly. It is currently not possible to differentiate stillbirths that arise secondary to late second trimester termination of pregnancy from those that occur for other reasons. The most important finding in this report is the progressive trends of reduced risk of stillbirth in pregnancies that ended in birth at or after 28 weeks of gestation. Some of this reduction in risk of stillbirth may be due to a shift in mortality to earlier gestations. However, when considered in relation to the overall decline in stillbirth rates over time for older women, this may suggest that some interventions in later pregnancy may have been of benefit and that further reductions in stillbirth are possible.

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