Feminist and disability scholars have critiqued the role of prenatal testing technologies in fostering parental expectations to give birth to “perfect” children. However, in the case of postnatal screening for genetic disorders, identifying large numbers of asymptomatic infants brings previously hidden imperfections into critical relief. Consequently, newborn screening technologies have altered the day-to-day landscape of early childrearing and development for many families. Drawing on ethnographic fieldwork in a California pediatric genetics clinic, we describe how newborn screening creates ambiguous forms of biogenetic abnormality, foreshadowing a life of incipient disorder for children, families, and health care providers and so destabilizing parents’ hopes of having a healthy child. By demonstrating key points of convergence and divergence between the social consequences of prenatal and postnatal screening, we expand the analytic gaze on reproductive technologies and establish newborn screening as a vibrant locus of inquiry for the anthropology of reproduction.