Monitoring of risk factor/outcome combinations: a valuable supplement to birth defect monitoring.

Since the thalidomide disaster in the early sixties many birth defect monitoring systems and registries have been set up to detect changes in the frequencies of specific birth defects. The primary methods of monitoring have been the statistical analysis of data on birth prevalences and teratologic analysis. The yield of this monitoring effect has nevertheless been low when one considers the lack of etiologic factors detected in this way. We therefore propose an additional strategy involving (periodic) classification of all cases in a birth defect registry according to possible risk factors and notified anomalies coupled with a search for specific associations between risk factors and (patterns of) anomalies. We here present data showing the sensitivity of the method. Sensitivity was studied by looking at some already well known associations between risk factors and congenital anomalies in our registry involving 1850 cases. The associations studied were neural tube defects and maternal use of valproic acid, numerical chromosomal anomalies and advanced maternal age, gastroschisis and low maternal age, and autosomal recessive disorders and parental consanguinity. Each of these associations was apparent in the registry, suggesting that risk factor/outcome monitoring as described here is a potentially strong method for finding new etiologic factors in birth defects.