 In any case, pregnant women remain an official ‘vulnerable group’ under the federal policies governing human subjects research, and are exempt from the inclusion mandate. Indeed, virtually all clinical research excludes pregnant women out of purported concern for teratogenic effects on fetuses, while even trials for interventions not classified as potentially teratogenic routinely exclude pregnant women (Shields and Lyerly 2013). Ongoing exclusion stymies development of safe and effective medical interventions for pregnant women, whose metabolism, blood volume, hormones, immune system, and other bodily systems are affected by pregnancy in ways that impact their response to medication (Blehar et al. 2013). It also places fetuses at risk; out of the 468 medications approved in the United States in 2002, 91% pose an unknown risk to fetuses (Lyerly, Little, and Faden 2008b). While the lacuna of reliable evidence regarding safe and effective medical interventions for pregnant women and their fetuses is widely acknowledged as a problem, it has not, in general, shaken the consensus that it is unethical to put fetuses at unknown risk for the purposes of research. Often the thalidomide crisis of the 1970s is cited as an example of the potential dangers of exposing fetuses to drugs, and hence as an object lesson in the need for precautionary principle to govern our practices of including pregnant women in research. But if the welfare of fetuses is our primary concern, we ought to take the opposite lesson from the thalidomide disaster: it is precisely because thalidomide was not systematically tested before being prescribed that so many babies were affected (Ibid.).