'Something there is that doesn't love a wall': histories of the placental barrier.

This article appraises the late twentieth century maxim that prior to thalidomide's clarion call in 1961, a generic "we" believed that the fetus was protected from external insult by the placental barrier. Complicating this truism, we demonstrate that the placenta was, since early in the twentieth century, conceived of as a site of constant passage of entities both necessary to, and dangerous for, fetal development. Moving between evidence from specialist journals, obstetrics textbooks, and pregnancy advice manuals, we argue that the placental barrier writ large only emerged as an explicit actor after the medical community was disillusioned with it: it became something that does not exist. The article proposes that the nostalgia for a barrier lost constructs the modern-day fetus as more exposed and vulnerable than if "we" had never imagined this protection in the first place. The rhetorical shorthand of the erstwhile placental barrier has both deflected more nuanced accounts of the thalidomide story and contributed to the increasing surveillance of pregnant women's behavior, particularly in late twentieth century North America.