Temporal trends in Canadian birth defects birth prevalences, 1979-1993

The Canadian Congenital Anomalies Surveillance System monitors birth defects reported for stillborns, newborns and infants during the first year of life. Data are available through the 1980s and early 1990s for Ontario, Manitoba and Alberta, and since 1984 for an additional four provinces. Fifty-seven routine monitoring categories and 15 summary categories were examined for temporal trends. Comparing the period 1979-1981 with 1991-1993, the reported birth defect case birth prevalence increased by 0.2% and the total birth defects birth prevalences by 2.5%. The birth prevalence of central nervous system defects decreased by 8.2%; the reported birth prevalence increased for congenital heart defects by 41%, urinary defects by 127%, Down syndrome by 13% and other chromosomal defects by 47%. Further investigation of individual defects would be required to evaluate the degree to which changes in reported birth prevalence reflect changes including the availability and use of specific diagnostic procedures. The work highlights the need to expand the surveillance system to include all affected pregnancies where an anomaly has been detected antenatally.