[National confidential enquiry into maternal deaths in France, a 25-year enhanced surveillance system, essential for the reliable characterization of maternal deaths].

Although maternal mortality is rare in wealthy countries, it remains a fundamental indicator of maternal health. It is considered to be a "sentinel event", the occurrence of which indicates dysfunctions, often cumulative, in the healthcare system. In addition to the classic epidemiological surveillance findings - number of deaths, maternal mortality ratio, distribution of medical causes, sub-groups of women at risk - its study, through a precise analysis of the history of each woman who died, enables to highlight areas for improvement in the content or organisation of care, the correction of which will make it possible to prevent not only deaths but also upstream morbid events involving the same mechanisms. To achieve this dual epidemiological and clinical audit objective, an ad hoc "enhanced" system is needed. France has had such a system since 1996, the Enquête Nationale Confidentielle sur la Mortalité Maternelle (ENCMM), under the joint supervision of Santé Publique France and Inserm. The ENCMM method aims to identify maternal deaths exhaustively and reliably up to 1 year after the end of pregnancy, and to document each death as fully as possible. The 1st step is the multi-source identification (direct declaration, death certificates, linkage with birth certificates, hospital stay database) of women who died during pregnancy or in the year following its end. The 2nd step is the collection of detailed information for each death by a pair of clinical assessors. The 3rd step is the review of these anonymised documents by the National Expert Committee on Maternal Mortality, which establishes the maternal nature of the death (causal link with pregnancy) and, with a stated aim of improvement rather than judgement, assesses the adequacy of care and the preventability of the death. The summary of the information gathered for maternal deaths in the 2016-2018 period is presented in the other articles of this special issue.