Severe Maternal Morbidity: Fundamental Concepts

Despite the importance of severe maternal morbidity (SMM) as a medical concern, there is a lack of consensus on several issues related to this topic. This article reviews fundamental concepts associated with SMM, and provides a historical and scientific perspective on these critical issues. SMM is defined as the population rate of serious illnesses in pregnancy, childbirth, or the puerperium. The SMM rate depends on the component severe maternal illnesses included in composite SMM, the rigor with which these components are defined, and the data sources used for surveillance (among others). These issues pose a serious challenge for spatiotemporal comparisons of SMM, especially for between-country comparisons of composite SMM rates. The different severe maternal illnesses included within composite SMM display substantial heterogeneity in terms of frequency, clinical burden of illness, and population impact. Other concerns include the need to address SMM in early pregnancy hospitalizations and postpartum readmissions; the need for nuanced interpretation of adjusted rates; and whether assigning a singular underlying severe illness is preferable to assigning one or more severe illnesses for each woman. Finally, the heterogeneity of the composite measure warrants careful consideration of the need for an all-inclusive composite outcome versus a more restricted/specific outcome depending on the study question or surveillance priority. Prevention programs addressing SMM need to focus on component illnesses and identify opportunities for intervention based on case reviews or epidemiologic analyses of risk factors for the specific illness. There is a lack of consensus on several concepts related to SMM, and this calls for a careful consideration of the clinical and epidemiologic issues related to quantifying and interpreting SMM rates.