This chapter examines the definitions of prematurity over time and specifically explores how racial science has been used to animate the definitions and etiology, or causes, of premature birth. This chapter focuses on the birth stories of four women, who gave birth prematurely in different centuries, between the nineteenth century and the present, to shed light on the temporality of Black women’s birth outcomes. The birth stories, including one contained in Incidents in the Life of a Slave Girl, an autobiographical narrative by Harriet Jacobs, highlight questions about the definition and etiology of prematurity. The stories also illustrate some of the clinical causes of premature birth and present the situations that women describe as evidence of medical racism.