Congenital Anomalies in Canada:

Technical Appendix

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The Canadian Congenital Anomalies Surveillance System (CCASS) Data Exploration Tool provides an overview of 38 congenital anomalies in Canada. Anomalies have been grouped into 12 categories (see below for more details on diagnostic coding). The data covers the years 2008 to 2023 and includes a follow-up period of one year after birth; data from Quebec includes livebirth data from 2008 to 2022.

This version of the data tool has been updated with more recent data and modified from the previous version (2022) to present data by total cases (confirmed and suspected cases combined). Approximately 93% of all major congenital anomaly cases are considered ‘confirmed’, meaning that they are established diagnoses. The remaining 7% may be considered ‘suspected’ cases, meaning that they are identified by a prefix in the Canadian Institute for Health Information - Discharge Abstract Database (CIHI-DAD) indicating that there may be some uncertainty in the diagnosis. In many cases, the diagnosis may be listed as ‘suspected’ because the infant required follow-up outside hospital by a pediatric specialist (e.g., genetics). This is more frequent in smaller jurisdictions or in smaller hospitals. Prevalence by suspected only and confirmed only cases are presented under the Supplemental Statistics tab.

Small cell counts, particularly for rarer conditions, can result in large fluctuations of estimates over time therefore trends with small cell counts should be interpreted with caution since small counts could make yearly fluctuations appear more pronounced.

Data Source:

• All data (except for Quebec) come from the CIHI-DAD.
• Data from Quebec comes from its provincial congenital anomalies program and utilises the Maintenance et exploitation des données pour l'étude de la clientèle hospitalière (MED-ÉCHO).
• Population includes all livebirths and stillbirths, except in Quebec where it contains only livebirths.

Congenital Anomalies Diagnostic Coding:

• The 38 congenital anomaly conditions (grouped into 12 categories) were defined using the International Statistical Classification of Disease and Related Health Problems, Tenth Revision, Canada (ICD-10-CA) codes. These selected conditions align with international reporting on congenital anomalies, such as EUROCAT or ICBDSR. See table below for details on ICD-10-CA codes used for the analysis.

Methodology:

• To protect privacy, data with cell counts less than five have been suppressed. In some instances, this meant suppressing more than one category to prevent any residual calculations. However, Quebec data with cell counts of less than five were rounded to five or zero, based on the methods established for their provincial congenital anomalies program. As only aggregated data are provided to PHAC, this may have contributed to higher case counts in Quebec compared to other jurisdictions.
• All estimates were calculated per 10,000 total births with the exception of Turner syndrome which is per 10,000 total female births and undescended testes and hypospadias which are per 10,000 total male births.
  • Microcephaly (ICD-10 code Q02) continues to be excluded from the Central Nervous System grouping and all subsequent calculations due to issues with accuracy in case ascertainment.
• National estimates include all congenital anomalies in Canada regardless of place of residence (i.e. province or territory is unknown). As such, national totals will differ from disaggregated totals by province/territory.
• Provincial and territorial analyses are shown by province or territory of maternal residence.
  • There are a number of social, economic and demographic factors that may contribute to geographical differences seen in the data (e.g. socio-economic differences, food insecurity, access to care issues (e.g. lack of access to a hospital)). The data is limited in its capacity to provide individual risk factor information to help explain these regional variations.
  • Small cell counts, particularly in Northern Canada, can result in large fluctuations of estimates for a given condition over time. This may not reflect a drastic increase or decrease, but rather it is a reflection of less stable estimates due to small cell counts.
• Denominators for data shown by jurisdiction include the total number of births in the specific province/territory during the specified time-period.

Statistical Analysis:

Test for trends were calculated using Cochrane Armitage test for linear trends with α=0.05.
Total prevalence was calculated as follows:

• (total number of cases with one or more major congenital anomaly / total number of births* (livebirths and stillbirths)) × 10,000 (*note: data from Quebec only contain livebirths)

Case fatality rates were calculated as follows:

• (all deaths with a specific congenital anomaly / all livebirths with a specific congenital anomaly) × 100

Livebirth prevalence was calculated as follows:

• (all congenital anomaly cases among livebirths / total births) × 10,000

Stillbirth prevalence was calculated as follows:

• (all congenital anomaly cases among stillbirths / total births) × 10,000

Suspected prevalence was calculated as follows:

• (all congenital anomaly cases with a suspected diagnosis / total births) ×10,000

Confirmed prevalence was calculated as follows:

• (all congenital anomaly cases with a confirmed diagnosis / total births) × 10,000

Limitations:

• The Canadian Congenital Anomalies Surveillance System (CCASS) under ascertains cases that are detected prenatally and/or have high mortality rates (where the likelihood of survival is low) which often result in a termination of pregnancy at less than 20 weeks gestation. For example, anomalies such as anencephaly, where the life expectancy is limited to just a few days after birth, or chromosomal anomalies which can be detected as early as nine weeks of gestation, are often terminated early in the pregnancy (<20 weeks), and are not included in our data sources. Therefore, certain anomalies are under reported.
• Stillbirth data includes spontaneous fetal deaths and those due to elective terminations of pregnancy. Any termination of pregnancy occurring prior to 20 weeks gestation are missing from this data.
• Anomalies which resulted in a stillbirth (e.g. Neural Tube Defect, chromosomal anomalies) are likely underrepresented in the province/territory disaggregation. Place of residence is often missing from stillbirth records and therefore, missing from jurisdictional comparisons. These cases are included as part of the national totals.

References