Prenatal diagnosis—the practice of monitoring fetal development and spotting potential problems—has radically changed the experience of pregnancy for tens of millions of women worldwide. The development of prenatal diagnosis was the result of a partly contingent coming together of four technical innovations—amniocentesis (sampling of the amniotic fluid), the study of human chromosomes, the description of ‘markers’ of fetal anomalies in maternal blood and obstetric ultrasound—and a social innovation: the liberalization of abortion. The initial stimulus for the development of prenatal diagnosis was the wish to prevent the birth of children with hereditary pathologies. In the 1970s and 1980s the widespread diffusion of prenatal diagnosis was strongly favoured by the desire to reduce the incidence of Down syndrome, a condition redefined as a public health problem. In the late twentieth century, the improved resolution of obstetric ultrasound favoured the direct observation of numerous fetal anomalies, but also the identification of ultrasound ‘risk markers’—morphological changes that indicate an increased probability of fetal problems. In the early twenty-first century genomic techniques again expanded the possibilities for studying the living fetus, opening new questions and creating new dilemmas.