How do we know if an exposure is actually teratogenic in humans?

The only way we can be certain that an exposure is teratogenic in humans is to recognize that it causes birth defects in babies. The goal of clinical teratology research is, therefore, to identify when a teratogenic exposure has harmed babies as quickly and effectively as possible. We use several kinds of human data to characterize teratogenic effects-case reports, case series, pregnancy registries, cohort studies, case-control studies, and record linkage studies. Each approach can be helpful, but each has limitations as well. Drawing a causal inference requires analysis of all available data, their consistency, and their biological plausibility.