This article explores the ways in which ultrasound screening influences the temporal dimensions of prevention in the obstetrical management of pregnancy. Drawing on praxeographic perspectives and empirically based on participant observation of ultrasound examinations in obstetricians' offices, it asks how ultrasound scanning facilitates anticipatory modes of pregnancy management, and investigates the entanglement of different notions of time and temporality in the highly risk-oriented modes of prenatal care in Germany. Arguing that the paradoxical temporality of prevention--acting now in the name of the future--is intensified by ultrasound screening, I show how the attribution of risk regarding foetal growth in prenatal check-ups is based on the fragmentation of procreative time and ask how time standards come into play, how pregnancy is located in calendrical time, and how notions of foetal time and the everyday life times of pregnant women clash during negotiations between obstetricians and pregnant women about the determination of the due date. By analysing temporality as a practical accomplishment via technological devices such as ultrasound, the paper contributes to debates in feminist STS studies on the role of time in reproduction technologies and the management of pregnancy and birth in contemporary societies.