This essay examines the portrayal of modern Black motherhood in Nella Larsen's Harlem Renaissance novel, Quicksand (1928). Writing in a cultural landscape dominated by discourses of racial uplift, scientific motherhood and eugenics, I argue that Larsen critiques and ultimately refuses the limited literary, medical and political terms available for representing Black motherhood in the early twentieth century. My readings centre Larsen's understudied career as a nurse; prior to becoming a writer, Larsen worked as Head Nurse at the Tuskegee Institute in Alabama and as a public health nurse for the Department of Health in the Bronx. I consider how this professional experience informed her fictional depiction of modern Black motherhood, drawing on archival materials to demonstrate how her novel complicates contemporaneous medical and cultural attitudes towards Black motherhood and resists the eugenic demands delineating what constitutes 'good' and 'bad' motherhood. Engaging contemporary Black feminist theories of refusal and Black motherhood, I show how Quicksand is not only a critique of racist stigmatising discourses and practices but also of how racism limits the ways in which Black mothers' complexity has historically been represented.