The Hungarian congenital malformation monitoring system.

The Hungarian Congenital Malformation Monitor has been operating since 1973 in order to detect the temporal and regional clusters of 12 indicator congenital malformations as early as possible. This Monitor takes part in the International Clearinghouse for Birth Defects Monitoring System. Three continuously increasing trends were detected in 1973--1976. They may be connected with the more complete notifications, although the increase of limb reduction deformities are only partly explained by this factor. Transitional (quarterly) significant clusters were observed in the case of anencephaly (1974, IV), spina bifida (1974, II; and 1975, III; 1976, III), cleft lip +/- cleft palate (1974, III). The possibility of three technical biases (changes in diagnosis, notification and evaluation of the given congenital malformation) has to be excluded before accepting the fact of a real epidemic. Subsequently, a case-control epidemiological study by personal interviews and with matched controls has to be performed.