Pregnancy Care Guidelines

Chromosomal anomalies

Chromosomal abnormalities is one of the primary cause of miscarriage during the first trimester. This chapter looks at the decision making method as to whether to have diagnostic testing. The process requires sensitive engagement with women a , partners and family members.

Fetal chromosomal anomalies identified through antenatal testing include:

  • trisomy 21 (Down syndrome), the most common chromosomal condition, which is characterised by distinctive facial features, some intellectual disability and heart or digestive tract problems
  • trisomies 18 (Edwards syndrome) and 13 (Patau syndrome), which are characterised by distinctive facial features, severe intellectual disability and other physical problems.

49.1 Chromosomal anomalies in Australia

The National Perinatal Statistics Unit last reported on congenital anomalies in Australia in 2002–03 (Abeywardana & Sullivan 2008). Trisomy 21 was the most commonly reported chromosomal condition at birth (1.11 per 1,000 births) but there was a high proportion (60%) of fetal deaths and terminations. When terminations were included, the estimated rate was 2.63 per 1,000 pregnancies. Trisomies 18 and 13 were associated with a large number of fetal deaths or terminations. All conditions were more common among women aged 40 years or older.

More recent Victorian data on antenatal diagnoses of chromosome anomalies based on amniocentesis and chorionic villus sampling results from 2013–15 gives an estimated detection rate of trisomy 21 of 2.61 per 1,000 births (1 in 380) (Hui et al 2016). Antenatal diagnoses of trisomies 18 and 13 were 0.5 (1 in 2,000) and 0.3 per 1,000 births (1 in 3,333) respectively (Hui et al 2016). Rates of trisomies 21, 18 and 13 were reported as 1.4, 0.5 and 0.1 in Queensland in 2010 (Howell et al 2011). Data from New South Wales in 2010 gives rates per 1,000 births (ie without terminations included) of 0.5 for trisomy 21 and 0.1 for trisomies 18 and 13 CEE 2012. In New South Wales, the number of reported terminations of pregnancy associated with chromosomal anomalies rose from 246 in 2004 to 323 in 2009 CEE 2012.


  • Abeywardana S & Sullivan EA (2008) Congenital Anomalies in Australia 2002–2003. AIHW Cat. no. PER 41. Sydney: Australian Institute of Health and Welfare National Perinatal Statistics Unit.
  • CEE (2012) New South Wales Mothers and Babies 2010. Sydney: NSW Ministry of Health (Centre for Epidemiology and Evidence).
  • Howell S, Endo T, McLeod S-L et al (2011) Congenital Anomalies in Queensland: 1 July 2007 to 30 June 2010. Brisbane: Health Statistics Centre, Queensland Health
  • Hui L, Muggli EE, Halliday JL (2016) Population-based trends in prenatal screening and diagnosis for aneuploidy: a retrospective analysis of 38 years of state-wide data. BJOG 123(1): 90-7.
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