Data quality, availability and interpretation
Due to rounding, percentage totals may not add to 100%.
A baby may have more than one type of anomaly and be counted in more than one type of anomaly category. A baby will only be counted once within each anomaly category. Given this, the sum of individual categories will be greater than the total number of babies with any anomaly.
Every effort has been made to collect and report congenital anomalies data consistently, by using common data specifications and reporting using a similar notification period across jurisdictions. It should be noted, however, that there are differences in the scope and methods used to collect congenital anomalies data across jurisdictions, for example the sources of notification for congenital anomalies varies by jurisdiction (see Table 3).
|Congenital anomaly register
|Perinatal data collection
|Admitted patient collection
Note: Due to rounding, percentage totals may not add to 100%.
Differences in collection methods may impact national counts and comparability between jurisdictions. For example, in 2017:
- Victoria had relatively more reported cases of chromosomal anomalies and fewer cases of other types of anomalies. This may be due to improved screening and testing for chromosomal anomalies and notifications from cytogenetic laboratories (prenatal diagnosis). Notifications to the VCAR are not mandatory in Victoria, and this may be a factor in the smaller number of notifications for other types of anomalies, compared to jurisdictions with mandated registers or those that use more active surveillance methods.
- Tasmania had a lower number of reported cases compared with other jurisdictions (except Victoria and Northern Territory). This may reflect the narrower notification period of their collection – the perinatal period only, compared with jurisdictions that include cases diagnosed up to 12 months of age.
- The Northern Territory had a relatively low number of reported cases compared with other jurisdictions. This may be due to interstate transfers of babies identified antenatally with major anomalies who require birthing in a specialist tertiary facility. In addition, only the primary anomaly associated with a particular syndrome is reported.
- Queensland had relatively more cases across some body systems (including for example circulatory, urinary, respiratory and musculoskeletal anomalies) and a higher rate for any anomaly overall. This may reflect the multiple sources of notifications and data linkage processes used in this collection (including admitted patient data).
- The Australian Capital Territory perinatal data contains cases of New South Wales residents giving birth in the Australian Capital Territory – the proportion of women giving birth who were non-residents was 15.6% in 2017. In looking at these data it is important to note that births to non-residents may include a disproportionate number of high-risk and multi-fetal pregnancies associated with poorer perinatal outcomes. Women with high-risk pregnancies may be transferred from smaller centres in New South Wales to the Australian Capital Territory to give birth.
More information about the NCADC can be found in the National Congenital Anomaly Data Collection, 2023 Quality Statement.
Comparing NCADC data with jurisdictional reports
The scope for reporting from the NCADC may be different to the scope for reporting from jurisdictional congenital anomaly collections. The AIHW harmonised the national data for reporting around the classification system and the notification period used, and the anomalies included for reporting. This means the numbers and rates in this report may differ from those reported by individual jurisdictions.
Differences between national and jurisdictional reporting may be due to:
- the AIHW reporting on anomalies in babies born in 2017 and diagnosed up to 12 months of age – reports in Victoria are based on anomalies in babies reported in 2017, rather than the year of birth
- the AIHW including data from the admitted patient data collection for New South Wales – in New South Wales, congenital anomalies reporting is based on register data only and does not include data sourced from their admitted patient data collection
- terminations of pregnancy being included in reports in some jurisdictions, regardless of gestational age, for example in reporting in Queensland, South Australia and Victoria
- some jurisdictions, for example, Queensland and South Australia, having a broader scope for reporting with respect to anomaly inclusions or notification periods.
See Table 2 for further information on jurisdictional congenital anomaly reporting.
The term ‘women giving birth’ is used when referring to mothers, whereas ‘babies’ refers to births.
This report uses the terms ‘woman’ and ‘women’ to mean ‘female' when referring to data collected in the National Congenital Anomalies Data Collection (NCADC) and the National Perinatal Data Collection (NPDC) as these data sources are based on sex. Information on gender is not recorded in these data collections. ‘Woman’ and ‘women’ typically refers to groups of people aged 18 years and over, however in this report people who were pregnant or gave birth aged less than 18 are included.
It is acknowledged that this report includes people who do not identify as women or mothers, and that individual parents and families may use different words to those used in this report. This may include women, transgender men, intersex people, non-binary and gender diverse people.
Data availability and timeliness
Data are presented on babies with in scope congenital anomalies in the 2017 birth cohort, that were diagnosed up to 12 months of age and the women who gave birth to these babies (see Reporting inclusions). It is not possible to provide national data on all cases diagnosed in the 2017 birth cohort, due to differences in collection methods across jurisdictions. This report does not include anomalies that were:
- terminations of pregnancy before 20 weeks’ gestation
- diagnosed after 12 months of age, and for Tasmania after the birthing episode
- diagnosed in Western Australia, as these data were not available.
Anomalies were also excluded where data were not available across all reporting jurisdictions, or if they did not have significant medical, social or cosmetic outcomes – these are sometimes referred to in other literature as minor anomalies (see Reporting exclusions).
The numbers and rates presented will therefore underestimate the overall prevalence of congenital anomalies in Australia. It is estimated that around 12–17% of anomalies are diagnosed after 12 months and before 6 years of age (Bower et al. 2010; Gibson et al. 2016). This may be lower or higher depending on the type of anomaly. Analysis of the data supplied in 2017 by South Australia indicates around 15% of anomalies in their 2017 birth cohort were diagnosed after 12 months of age and would be excluded from this national report.
This report is based on the most recent data available across reporting jurisdictions. Data in the NCADC are sourced from various state and territory data collections and collection methods vary. Each collection involves data entry, classification and validation and may include data linkage processes. Some congenital anomalies data collections have long notification periods (up to 5 or 6 years of age), which means the data for a particular birth cohort may take years to finalise. Jurisdictions have noted the following issues in the supply of congenital anomalies data:
- Resources and funding
The collection of anomalies data is mandated in 4 jurisdictions. There are resource implications for jurisdictions to develop and maintain a congenital anomalies collection.
- Complexity of case ascertainment
Cases are difficult to ascertain due to their low prevalence rates. Jurisdictions have different methods of case ascertainment and rely on multiple data sources to identify cases of congenital anomalies. There may be timeliness issues around getting data from these different sources and following up sources for case ascertainment. Linkage with other data collections, while improving case ascertainment, may also affect the timely supply of anomalies data as data will need to go through de‑duplication and validation processes.
- Notification period
Timeliness is also dependent on the notification period used. For some congenital anomaly collections (for example, those that collect data until 6 years of age), birth cohort data are incomplete for the first few years.
The Australian Congenital Anomalies Monitoring System (ACAMS) is an AIHW collection containing data on babies with a diagnosed congenital anomaly between 1981 and 2003. The most recent reports from this collection were published in 2007 (Abeywardana et al. 2007), 2008 (Abeywardana and Sullivan 2008) and 2011 (Macaldowie and Hilder 2011). Data in this report are not directly comparable with previous ACAMS reports, due to differences in scope and the period of notification used.
Abeywardana S, Karim M, Grayson N and Sullivan EA (2007) Congenital anomalies in Australia 1998–2001, Sydney: AIHW National Perinatal Statistics Unit.
Abeywardana S and Sullivan EA (2008) Congenital anomalies in Australia 2002–2003, Sydney: AIHW National Perinatal Statistics Unit.
Bower C, Rudy E, Callaghan A, Quick J and Nassar N (2010) Age at diagnosis of birth defects, Birth Defects Research. Part A, Clinical and Molecular Teratology, 88(4), 251–255. doi:10.1002/bdra.20658
Gibson C, Scott H, Haan E and Scheil, W (2016) Age range for inclusion affects ascertainment by birth defects registers, Birth Defects Research. Part A, Clinical and Molecular Teratology, 106(9), 761–766. doi:10.1002/bdra.23534
Macaldowie A and Hilder L (2011). Neural tube defects in Australia: prevalence before mandatory folic acid fortification, Canberra: AIHW.
Data gaps and future directions
The AIHW is working to re-establish a national congenital anomalies data collection. The collection and reporting of congenital anomalies data will assist in monitoring prevalence and trends in congenital anomalies and in planning services for these conditions. There are differences in the way cases are identified across jurisdictions and this will affect both jurisdictional and national counts. Further work is needed to standardise congenital anomalies data across jurisdictions. The next phase of work includes improving both the consistency and timeliness of data provided to the NCADC, supporting the inclusion of data from Western Australia into the collection, and embedding collection and reporting processes.