Population surveillance of congenital malformations. Possibilities and limitations.

The paper discusses the possibility of detecting newly introduced teratogenic agents by a population surveillance of congenital malformations. In practice, only outbreaks of previously rare malformations or combinations of malformations can be detected by such systems. The most important aspect of malformation surveillance is therefore a detailed reporting of malformations whereas statistical techniques play a minor role. For ongoing surveillance, a high ascertainment level is less important than speed and amount of detail. For studies of long-time changes in malformation rates, ascertainment must be as complete as possible. Such changes have been identified repeatedly, but are usually explained by changes in diagnosis, ascertainment or population characteristics.