New South Wales Mothers and Babies Report 2010.
Chapter 9, Congenital Conditions includes the most recent pregnancy and birth statistics on babies with Down syndrome, pp 92 - 100. The statics are listed in tables and graphs indicating trends, but no specific comment is made in the text about trends related to Trisomy 21.
This report updates the NSW the statistics referred to in this 2009 post which is still often accessed.
NSW Mothers and Babies Reports 1996 - 2010 are now individually linked from this NSW Health web page.
National data is collated by the Australian Institute for Health and Welfare, which has published it online and in print from time to time, as Congenital Anomalies reports - but they are currently listed as 'not reported on'.
The most recent AIHW data on the birth incidence of Down syndrome is a rate of 11:10,000 given as the rate of Down syndrome occurring among infants at birth 1998 - 2003, in the report, A picture of Australia's children 2009, Part ll: How healthy are Australia's children, p 11 - table of indicators. In Section 7, Congenital Anomalies, Table 7.1 (p 29) gives rates and numbers of babies born with Down syndrome in indigenous and non indigenous populations (no significant difference), and by geographical location with commentary on differences, and notes that termination because of Down syndrome occurred at more than twice the birth rate (25:10,000).