Search for teratogenic risks with the aid of malformation registries

A summary is given of experiences in the use of the Swedish registries of birth defects for causal epidemiological studies. Case-control studies and cohort studies are described and exemplified. The application of case-control techniques to cohorts of women selected for probable or possible exposure is also described. The importance of using large-scale registry studies in the search for common but low-risk teratogens is stressed.