The distribution of anticonvulsant drug therapy was studied in 318 malformed 
infants with known histories of maternal epilepsy. Data on the infants was 
collected from six birth defect monitoring programs in Europe and South America. 
Use of specific types of anticonvulsants varies widely among reporting 
countries. Heterogeneity of drug-malformation distribution, was analyzed to 
determine whether use of specific drugs were linked to specific malformations. A 
significant association was seen between maternal use of valproic acid and spina 
bifida, and a weaker, non-significant one between carbamazepine and spina 
bifida. Facial clefts were associated with both diphenylhydantoin and 
phenobarbitone use and also with polytherapy. These differences indicate that 
the actual drug used is significant for the teratogenic process. The technique 
may be useful in analysis of other drug-related teratogenic questions.