||Prenatal diagnosis (PND) has gradually established itself as part of the pregnancy monitoring process, with a view to reducing the number of births of children exposed to disability by combining the use of biomedical tools with laws that authorise abortion in cases of foetal pathology. This article looks at how laws which vary from one country to another modulate the way in which PND practices are organised on a daily basis, determine the discourse of practitioners and lead them to adopt specific stances during prenatal consultations with couples coping with a foetal anomaly. We present a comparative ethnographic study, which took place between 2009 and 2011 in France and Brazil, in reference units, based on observation of consultations, professional meetings, and interviews with health practitioners. The fact that access to abortion due to foetal pathology is possible in France, and criminalised in Brazil, conditions how doctors analyse the framework of their medical practice and approach the issue of disability with couples during consultations. In France, practitioners would appear to be satisfied with a professional framework that they themselves created. Faced with prognostic uncertainty, the legal obligation to inform encourages them to discuss all of the potential complications of the diagnosed anomalies and leads them to provide probabilistic information about the life of the child to be, supported by evidence-based medicine. In Brazil, in the public service, the lack of access to abortion has created a malaise among practitioners who criticise this impediment to the objective nature of their practice and to the quality of the information that they provide. Some use prognostic uncertainty to direct the thoughts of women and couples towards the dynamics proper to each individual human trajectory within a given family and a specific social environment.