Surveillance of malformations

Abstract

The authors review the usefulness of monitoring and surveillance of congenital malformations and describe the monitoring system that has been in operation in England and Wales since 1964. The Office of Population Censuses and Surveys receives, from the Medical Office of each of 98 areas, information on each malformed child notified in the area. Malformations observed at birth are indicated on a check list of 66 categories which are then further classified into 28 groups, allowing for more than 900 comparisons. Monthly tabulations are produced 5 to 6 mth after the babies are born. 2 Types of statistical monitoring tests are used in the surveillance of the data. The first involves the calculation of an expected number of malformations for each class of abnormality and for each area. This is compared with the observed frequency and the standard normal deviation is calculated. When this exceeds a 'critical' value, it serves as a warning that the incidence of that malformation is above or below the average at that time. The 2nd statistical surveillance test uses the cumulative sum (cusum) technique which provides the ability to detect quickly any shift in mean level of malformations in a time series, in relation to a reference value. Data from such surveillance systems are useful in various ways to those responsible for health care. (Myrianthopoulos - Bethesda, Md.)