identify several thousand possibly teratogenic agents, with roughly half of them having been shown to cause birth defects in laboratory animals. Thus considered, it might appear that the relevance of teratogens to human pregnancies can easily be classified and understood. Further, the value of a compiled list of agents toxic to good birth outcomes is difficult to overstate. However, it is extremely important to emphasize that reported results of teratogenic identifications in laboratory animals do not necessarily implicate an agent in human subjects. No less significant is a fact connected to it: that there are almost insurmountable methodological challenges to empirically verifying the scope and limit of teratogenic functionality.
Results of teratogenic studies of human subjects--who obviously cannot be subjected willy nilly to laboratory trials of suspected teratogens--are extremely rare, a point driven home repeatedly in the literature (e.g., Wolkomir, 1996; Wayne & Apgar, 1998). Only observed pathologies (e.g., congenital birth defects) can be traced
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