3.6 Age of Inclusion

Countries that have congenital anomalies surveillance programmes have different criteria for age of inclusion. Some include information about fetuses or neonates with a congenital anomaly ascertained only during the early neonatal period (see Table 3.1), while others include those ascertained up to 1 year of age and beyond (see Fig. 3.10).

Table 3.1. Periods of infancy
Periods of infancy
Time period Days
Neonatal 0–27
Early neonatal 0–6
Late neonatal 7–27
Post neonatal 28–364

Fig. 3.10. Age of inclusion in a congenital anomalies surveillance programme
Fig. 3.10. Age of inclusion in a congenital anomalies surveillance programme

Fig. 3.10. Age of inclusion in a congenital anomalies surveillance programme

Countries that have congenital anomalies surveillance programmes have different criteria for age of inclusion. Some include information about fetuses or neonates with a congenital anomaly ascertained only during the early neonatal period (see Table 3.1), while others include those ascertained up to 1 year of age and beyond (see Fig. 3.10).

The Western Australian Birth Defects Registry includes cases diagnosed up to 6 years of age. Fig. 3.11, derived from reference (13), indicates the cumulative percentage of cases with major external and internal congenital anomalies by age at first diagnosis.

The authors examined the age at diagnosis for all congenital anomalies notified to the Birth Defects Registry from 2000 to 2001. Nearly 60% of all major congenital anomalies were diagnosed during the first week of life, nearly 70% by the first month, nearly 90% by the first year, and nearly 100% by the sixth year.

Age at diagnosis is a critical component of the case definition. Typically, the higher the cut-off age, the greater the reported frequency of conditions, especially for conditions involving internal organs that may not be evident at birth. For example, whereas external anomalies such as neural tube defects and gastroschisis are evident at birth, some internal anomalies such as heart defects may not be identified until days, or even weeks or months after delivery. In addition, certain anomalies may require postnatal confirmation.

Fig. 3.11. Cumulative percentage of cases of major congenital anomalies by age at first diagnosis