3.3 Case Finding
Congenital anomalies surveillance programmes can decide the sources from which cases will be identified (see Fig. 3.5).
Using multiple sources may improve the completeness of case ascertainment by identifying cases that are not available from only one individual source. Additionally, it may improve the quality of the data, as having multiple sources may increase the amount and level of information available for a given case. For example, a diagnosis may not be possible in the delivery unit but may be established by specialists in the paediatric unit and further confirmed by laboratory tests. While the use of multiple data sources is more time consuming and delays the process of gathering information, it can improve overall case ascertainment and data quality.
Using a single source for case ascertainment does not allow for ascertainment of the majority of fetuses or neonates with a congenital anomaly in most settings. For example, Fig. 3.6 depicts a marked under-ascertainment of neural tube defects in Puerto Rico when cases were ascertained from vital records alone, compared with case ascertainment from multiple sources (e.g. logbooks in the delivery room, neonatal care units, paediatric units) used by the Birth Defects Surveillance Programme.