ARCHIVED: Introduction: Congenital anomalies surveillance in Canada: results of a 2006-2007 survey on availability of selected data variables in Canadian provinces and territories
This report contains information from a national survey that was conducted by the Maternal and Infant Health Section, Public Health Agency of Canada (PHAC) and the Demographic and Risk Indicators Working Group (DRIWG) of PHAC’s Canadian Congenital Anomalies Surveillance Network (CCASN) in 2006–2007. The survey was undertaken to determine to what extent there were common data variables collected on congenital anomalies in the various provincial and territorial systems across Canada. This work was carried out for the purpose of exploring alternatives to the current data sources and structure of the Canadian Congenital Anomalies Surveillance System (CCASS).
A congenital anomaly is a condition that results from an abnormality of structure, function or metabolism in one or more parts of the body and has the potential to seriously affect health, development or function.1,2 Although congenital anomalies, by definition, are present at birth, they may not be diagnosed until later in life. Major congenital anomalies are generally reported to affect an estimated three percent of all births.3 However, prevalence estimates of congenital anomalies vary depending on which anomalies are included and the method of ascertainment. In Canada in 2004, the prevalence at birth of congenital anomalies (including live born and stillborn babies with at least one congenital anomaly) was 4.8%.4
Congenital anomalies continue to be one of the leading causes of infant death in Canada.4 Nonetheless, the rate of infant death due to congenital anomalies has been decreasing.5,6 This trend has been well-described and is most likely the result of advances in prenatal diagnosis and termination of pregnancies in which fetal anomalies have been detected.6 Indeed, differences in rates of fetal and neonatal death due to congenital anomalies by birth weight, with increasing rates among those <500 grams and decreasing rates among those ≥ 500 grams, seem to support this conclusion.7
The impact of prenatal diagnosis and pregnancy termination notwithstanding, trends in mortality due to congenital anomalies have also been influenced by advances in medical and surgical treatment. This has lead to a documented change in the natural history of some congenital anomalies. For instance, there have been increases in the life expectancy of individuals with congenital heart disease8 and Down Syndrome9 over the past several decades. Given that individuals with these types of congenital anomalies typically experience health problems throughout their life span as a result of their anomaly, it could be argued that congenital anomalies are the ‘first chronic disease’. The importance of monitoring trends such as these is underscored by recent evidence that congenital malformations, deformations and chromosomal abnormalities (diagnostic codes originating in Chapter XVII of the International Classification of Disease, 10th revision10 [ICD-10]) represent the conditions with the highest average cost per acute hospital stay in Canada.11
Primary prevention efforts as well as changes in population-level risk factors and exposures are also contributing to a change in the epidemiology of some congenital anomalies. For instance, food fortification with folic acid has resulted in a significant decrease in the prevalence of neural tube defects in Canada.12 At a population level, maternal age, which is known to be an important risk factor for chromosomal-associated anomalies,13 has been increasing in Canada14 and other countries.15 This trend has likely affected the occurrence of pregnancies affected with anomalies such as Down Syndrome.13 However, because of the availability of prenatal diagnosis and termination of pregnancies in which fetal anomalies have been detected, the birth prevalence may be relatively unchanged, even while the overall frequency of Down Syndrome affected pregnancies (among live births, stillbirths and fetuses from terminated pregnancies) may be increasing.9 Figure 1, from Bittles and colleagues demonstrates this phenomenon for Down Syndrome in Western Australia where, between 1980 and 2004, the overall frequency of Down Syndrome during pregnancy (including fetuses from terminated pregnancies) more than doubled despite little change in the prevalence of live births and stillbirths with Down Syndrome.9
(Reproduced with permission from: Bittles, AH et al. Eur J Public Health 2006;17:221-225; doi:10.1093/eurpub/ckl103)
Figure 1 - Text Equivalent
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ARCHIVED - Figure 1 - Down syndrome live births, stillbirths, and fetuses from terminated pregnancies per 1,000 births in Western Australia 1980-2004
Figure 1 captures time trends for Down syndrome live births, stillbirths, and fetuses from terminated pregnancies per 1,000 births in Western Australia between 1980 and 2004, using a horizontal line graph. The x-axis represents years between 1980 and 2004, and the y-axis represents the rate per 1,000 births using a scale of 0.0 to 3.5. In 2004, the Down syndrome stillbirth rate per 1,000 births was 0.12 (lowest endpoint estimate on the y-axis), showing little change since 1980. The Down syndrome live birth rate per 1,000 births in 2004 was 1.10. The linear estimates for live births show some fluctuation in the early 1990s, but illustrate little overall change between the years 1980 and 2004. In contrast, the Down syndrome pregnancy termination rate per 1,000 live births increased markedly from less than 0.1 in 1980 to a rate of 1.72 in 2004 (endpoint estimate approximately midway on the y-axis). Despite little change in stillbirth and live birth rates between 1980 and 2004, the graph shows that the total rate of Down syndrome during pregnancy (including fetuses from terminated pregnancies) more than doubled to a rate of 2.94 by 2004 (highest endpoint estimate on the y-axis), highlighting the impact of prenatal diagnosis and subsequent termination of pregnancies on the changing prevalence of Down syndrome in Western Australia.
Maternal obesity and pre-pregnancy (i.e., non-gestational) diabetes are both associated with an increased risk for congenital anomalies16–20 and the prevalence of these two risk factors is increasing in both the general population21,22 and among pregnant women.23–25 There is evidence suggesting that infants conceived by assisted human reproduction (AHR) are at a higher risk of having a congenital anomaly, compared with infants conceived spontaneously; however, the etiology is not well-understood.26 AHR is increasingly used in Canada to achieve pregnancy – the number of births (live births and stillbirths) following a pregnancy achieved by AHR increased from at least 3,107 in 2003 to at least 3,210 in 2004,27,28 which represents approximately 0.9% of the total births in Canada for each of those years.29 In 2005, the number increased further to at least 3,554 births following AHR,30 representing approximately 1.0% of the total births in Canada.31
In 2002, a formal network for congenital anomalies surveillance was established by Health Canada. The Canadian Congenital Anomalies Surveillance Network (CCASN) is a national framework to support interdisciplinary collaboration and networking, bringing together research, surveillance and clinical and public health practices, with the ultimate goal of enhancing the quality of surveillance data and expanding our understanding of the etiology and natural history of congenital anomalies. It currently functions under the auspices of the Canadian Perinatal Surveillance System (CPSS) in the Maternal and Infant Health Section of the Public Health Agency of Canada.
To support the development and maintenance of high quality population-based surveillance systems of congenital anomalies that will provide information to improve the health of Canadian children and their families.
Goals and Objectives
- To enhance the range and quality of congenital anomalies surveillance activities in Canada;
- To develop and promote the use of minimum data sets and common definitions that will allow quality and consistency in surveillance activities in Canada;
- To be a resource for professional support, e.g. epidemiology, medical genetics and other disciplines, for new and developing surveillance activities;
- To facilitate collaborative congenital anomalies surveillance and research efforts among provinces and territories and with the international community;
- To facilitate the communication of information related to congenital anomalies for health professionals and the Canadian public;
- To foster educational opportunities in congenital anomalies surveillance and research.
The CCASN organizational structure consists of an Advisory Group and working groups that are task-specific.
In response to the thalidomide tragedy, the Canadian Congenital Anomalies Surveillance System (CCASS) was established by Health Canada in 1966. CCASS is a national surveillance database, which is managed by the Maternal and Infant Health Section in the Public Health Agency of Canada.
At the present time, the primary source of data for CCASS is the Discharge Abstract Database (DAD) administered by the Canadian Institute for Health Information. In addition, data for Québec are obtained from the Système de maintenance et d’exploitation des données pour l’étude de la clientèle hospitalière (Med-Écho), and data for Alberta originate from the Alberta Congenital Anomalies Surveillance System and are submitted directly to CCASS by Alberta Health/Vital Statistics.2
Limitations of the CCASS data have been previously noted and largely relate to the system’s reliance on administrative hospital records. These general limitations include, but are not restricted to, the use of ICD codes, with no opportunity for verification in most cases; the failure to capture congenital anomalies diagnosed after birth during an out-patient health care visit; the restriction (in most jurisdictions) of data collection on non-live births to fetuses meeting the criteria for stillbirth (generally ≥500 grams, or ≥20 weeks gestation); the lack of complete information on pregnancy terminations for fetal anomalies, which is an essential component of congenital anomalies surveillance today; the lack of data on maternal prenatal exposures and risk factors; and a lag time in availability of the data.2
In recent years, the list of limitations to the current national system has expanded. Previously, CCASS data were based on an ascertainment period for cases with congenital anomalies of one year after birth. Beginning in the fiscal year 2000-2001, new data access regulations made it impossible to ascertain such cases later than 28 days after birth.
Recognizing the inability of the current national system to provide complete, accurate and timely information on congenital anomalies, the Maternal and Infant Health Section and CCASN’s Demographic and Risk Indicators Working Group (DRIWG) undertook a national survey in 2006–2007. The survey was conducted to determine the degree to which there were common data variables collected on congenital anomalies in the various provincial and territorial systems across Canada.
This work was carried out for the purpose of exploring alternatives to the current data sources and structure of the Canadian Congenital Anomalies Surveillance System, such as an improved national congenital anomalies surveillance database assembled from anonymous data submitted directly by provincial and territorial systems.
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