Technical Appendix
Data Source:
- All data (except for Quebec) come from the Canadian Institute for Health Information - Discharge Abstract Database (CIHI-DAD).
- Data from Quebec comes from their provincial congenital anomalies program and utilises the Maintenance et exploitation des données pour l'étude de la clientèle hospitalière (MED-ÉCHO).
- Congenital anomalies identified among infants (from birth to age 1) between 2006 and 2020 were included for analysis, with the exception of data from Quebec which includes data from 2008 to 2020.
- Population includes all livebirths and stillbirths, except for Quebec which contain only livebirths.
- Please note: stillbirth data includes spontaneous fetal deaths and those due to elective terminations of pregnancy; however, these are likely an underestimation. Further, any termination of pregnancy occurring prior to 20 weeks gestation are missing from this data.
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, see Data Map for details on ICD-10-CA codes used for the analysis.
Methodology:
- To protect privacy, any data with small cell counts less than five have been either suppressed or combined.
- Where possible, congenital anomalies were reported by confirmed and suspected status.
- All rates 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.
- Undescended testes inclusion was changed to ≥ 37 weeks gestation (in previous versions this was reported for those >35 weeks).
- Microcephaly (Q02) was removed from the Central Nervous System grouping and all subsequent calculations due to issues with accuracy in case ascertainment.
- Proportions for infant sex were calculated as the total number of males or females over the total number of cases for a given condition (confirmed and suspected cases).
- Infants with an indeterminate sex were excluded from any sex-specific analyses.
- Rates for maternal age were calculated in a specific time-period (e.g. 2011-2015 and 2016-2020) by age group (e.g. <20, 20-24, 25-29, 30-34, 35-39, and 40+) per 10,000 total births.
- Missing maternal age were excluded from any age-specific analyses.
- National rates include all congenital anomalies in Canada regardless of place of residence (i.e. province or territory is unknown), infant sex and/or maternal age. As such, national totals will differ from disaggregated totals, as these cases are included in all national level calculations.
- Provincial and Territorial analyses is shown by ‘Province of residence’ as indicated by the postal code on the hospital admission record. This is a deviation from our previous methods, which reported by province or territory of occurrence (i.e. where the birth took place).
- A few considerations to this change in methodology: there are a number of factors, which may contribute to geographical differences seen in the data (i.e. socio-economic differences, food insecurities, access to care issues i.e. lack of hospital). The data is limited in this 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 rates for a given condition. This may not reflect a drastic increase or decrease, but rather it is a reflection of less stable rate due to small cell counts.
- Denominators for data shown by jurisdiction includes the total number of births in the specific Province/Territory during the specified time-period.
COVID-19 Pandemic Period:
Due to the impact of COVID-19 on hospitalizations (reduced births in the hospital), congenital anomalies data from 2020 need to be interpreted with caution, particularly when comparing with 2019 data. In particular, there were significant decreases in the total number of DAD records in 2020 versus 2019.
Acknowledgements:
The Canadian Congenital Anomalies Surveillance Section would like to thank their Provincial and Territorial partners and their Expert Advisory Committee for their review of the data and for providing invaluable feedback.