Newborn screening for genetic diseases has developed rapidly in Western countries. These biopolitics raise the question of birth as a sociological “knot” insofar as it is the threshold between the child and the fetus. The question therefore addressed in this text, based on a field study of newborn screening for cystic fibrosis in France, is that of the link between the quest for good health and the elimination of poor health. Do they reinforce each other or, on the contrary, are (...) they contradictory? I analyze the positions of both mothers of screened children and clinicians regarding the following three points: prenatal diagnosis to preclude sets of sick siblings, identification of heterozygous individuals, and generalized prenatal screening. This study shows how increasingly attentive patient care and an increasingly demanding approach to prenatal diagnosis reinforce one another. It also analyzes the role of taking action early on and evaluating the lives of sick or disabled people in this process. In conclusion, I engage a more general discussion about what I suggest calling a “quality life.”. (shrink)