The rapidly shifting field of epigenetics has expanded scientific understanding of how environmental conditions affect gene expression and development. This article focuses on two ongoing clinical trials—one in the United States and one in the United Kingdom—that have used epigenetics as the conceptual basis for testing the relationship between nutrition and obesity during pregnancy. Drawing on ethnographic research, I highlight the different ways that clinical scientists interpret epigenetics to target particular domains of the environment for prenatal intervention. Here I examine three environmental domains: the pregnant body, the home, and everyday experiences. In so doing, I show how different scientific approaches to epigenetics multiply concepts of “the environment,” while also individualizing responsibility onto pregnant bodies. Ultimately, I argue that how the environment is conceptualized in epigenetics is both a scientific and a political project that opens up questions of reproductive responsibility.