Ways Forward in Preventing Severe Maternal Morbidity and Maternal Health Inequities: Conceptual Frameworks, Definitions, and Data, from a Population Health Perspective.

Abstract

The United States ranks worse on maternal mortality than other high-resource countries (Tikkanen et al., 2020Tikkanen R. Gunja M.Z. FitzGerald M. Zephyrin L. Maternal mortality and maternity care in the United States compared to 10 other developed countries.https://www.commonwealthfund.org/publications/issue-briefs/2020/nov/maternal-mortality-maternity-care-us-compared-10-countriesDate: 2020Google Scholar). It is one of few countries where maternal mortality has not improved in recent decades (GBD 2015 Maternal Mortality Collaborators, 2016GBD 2015 Maternal Mortality CollaboratorsGlobal, regional, and national levels of maternal mortality, 1990–2015: A systematic analysis for the Global Burden of Disease Study 2015.Lancet. 2016; 388: 1775-1812Abstract Full Text Full Text PDF PubMed Scopus (544) Google Scholar). Racial/ethnic and geographic inequities in maternal mortality are substantial and persistent. Black and Native American individuals are particularly burdened, with at least two- to threefold higher mortality than the rest of the population (Admon et al., 2018Admon L.K. Winkelman T.N.A. Zivin K. Terplan M. Mhyre J.M. Dalton V.K. Racial and ethnic disparities in the incidence of severe maternal morbidity in the United States, 2012–2015.Obstetrics & Gynecology. 2018; 132: 1158-1166Crossref PubMed Scopus (97) Google Scholar). Severe maternal morbidity (SMM) is a sentinel or near-miss maternal health outcome proximate in severity to maternal mortality (Figure 1). SMM encompasses unexpected outcomes of labor and birth that put women most at risk of dying, such as eclampsia, hemorrhage, cardiovascular events, sepsis, and organ failure (American College of Obstetricians, 2016Kilpatrick S.K. Ecker J.L. American College of Obstetricians and Gynecologists, the Society for Maternal-Fetal MedicineSevere maternal morbidity: Screening and review.American Journal of Obstetrics and Gynecology. 2016; 215: B17-B22Abstract Full Text Full Text PDF Scopus (106) Google Scholar). SMM is 50–100 times more common than maternal mortality, affecting 1–2% of people giving birth, and thus more feasible to study. Like maternal mortality, SMM has increased in recent decades (although the reasons for the increases are uncertain) (Leonard et al., 2019Leonard S.A. Main E.K. Carmichael S.L. The contribution of maternal characteristics and cesarean delivery to an increasing trend of severe maternal morbidity.BMC Pregnancy and Childbirth. 2019; 19: 16Crossref PubMed Scopus (44) Google Scholar) and disproportionately affects women of color (Admon et al., 2018Admon L.K. Winkelman T.N.A. Zivin K. Terplan M. Mhyre J.M. Dalton V.K. Racial and ethnic disparities in the incidence of severe maternal morbidity in the United States, 2012–2015.Obstetrics & Gynecology. 2018; 132: 1158-1166Crossref PubMed Scopus (97) Google Scholar). A better understanding of how and why SMM occurs is key to improving maternal health and preventing maternal mortality. This includes recognizing both clinical and social drivers of maternal morbidity (e.g., racism), and their modifiability. The objective of this commentary is to call attention to challenges to identifying population-level strategies for preventing SMM and its inequities, and to propose solutions. We focus on challenges to conducting research related to SMM within the U.S. context, although the points raised have broader global applicability. The challenges discussed include 1) the conceptual frameworks used to understand SMM, 2) defining SMM, and 3) the availability of data to assess SMM. By addressing these issues, we aim to advance research and efforts to improve health across the life course for people who give birth. Here, we use terms that are both gendered (e.g., maternal) and gender-neutral (e.g., individual) to be inclusive of the identities of all persons with capacity for pregnancy and birth, which span the gender spectrum (Moseson et al., 2020Moseson H. Zazanis N. Goldberg E. Fix L. Durden M. Stoeffler A. Obedin-Maliver J. The imperative for transgender and gender nonbinary inclusion: Beyond women's health.Obstetrics & Gynecology. 2020; 135: 1059-1068Crossref PubMed Scopus (40) Google Scholar). We conceptualize SMM and its inequities within a multidimensional causal chain of events framework that spans the “macrosocial” (i.e., structural and societal factors) to the “micro-clinical” (i.e., pathways from specific clinical precursors to specific SMM indicators) (Figure 2). Transformative, sustainable improvements require identifying effective interventions that span this entire continuum: preventing acute progression to life-threatening situations and interrupting higher-order social processes that threaten health. Transformative change will thus require centering on equity, which in turn requires acknowledging our historical legacy (Halfon et al., 2014Halfon N. Long P. Chang D.I. Hester J. Inkelas M. Rodgers A. Applying a 3.0 transformation framework to guide large-scale health system reform.Health Affairs (Millwood). 2014; 33: 2003-2011Crossref PubMed Scopus (51) Google Scholar; Kramer et al., 2019Kramer M.R. Strahan A.E. Preslar J. Zaharatos J. St Pierre A. Grant J.E. Callaghan W.M. Changing the conversation: applying a health equity framework to maternal mortality reviews.American Journal of Obstetrics and Gynecology. 2019; 221 (609.e601–609.e609)Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar) rooted in the historical context of the enslavement of Black Americans, the genocide of Native and Indigenous Americans, and a system of structural racism (i.e., mutually reinforcing systems that foster racial discrimination and differential access to resources and opportunities) that has led to intergenerational trauma for minoritized groups in the United States (Bailey et al., 2021Bailey Z.D. Feldman J.M. Bassett M.T. How structural racism works - Racist policies as a root cause of U.S. racial health inequities.New England Journal of Medicine. 2021; 384: 768-773Crossref PubMed Scopus (283) Google Scholar). Several conceptual and theoretical frameworks and approaches are particularly important to guiding research on SMM (Table 1). First, SMM research should be grounded within a broader context of reproductive health that acknowledges its multilevel, life course, and intergenerational nature (recommendation 1A). Reproductive health is influenced by experiences that span the entire life course and multiple generations, and that occur at multiple levels (e.g., individual, family, neighborhood, societal) (Halfon and Hochstein, 2002Halfon N. Hochstein M. Life course health development: An integrated framework for developing health, policy, and research.Milbank Quarterly. 2002; 80 (iii): 433-479Crossref PubMed Scopus (606) Google Scholar; Lu and Halfon, 2003Lu M.C. Halfon N. Racial and ethnic disparities in birth outcomes: A life-course perspective.Maternal and Child Health Journal. 2003; 7: 13-30Crossref PubMed Scopus (670) Google Scholar; McLeroy et al., 1988McLeroy K.R. Bibeau D. Steckler A. Glanz K. An ecological perspective on health promotion programs.Health and Education Quarterly. 1988; 15: 351-377Crossref PubMed Scopus (4172) Google Scholar). For example, adverse childhood events, as well as intergenerational poverty, may affect adult reproductive outcomes (Mersky and Lee, 2019Mersky J.P. Lee C.P. Adverse childhood experiences and poor birth outcomes in a diverse, low-income sample.BMC Pregnancy and Childbirth. 2019; 19: 387Crossref PubMed Scopus (20) Google Scholar).Table 1Recommendations for Improving Population-based Research on SMM1. Conceptual and theoretical frameworks to guide SMM research1A. Reproductive healthSMM research should be grounded in the broader context of reproductive health (not just “pregnancy” health), acknowledging that reproductive health is•Multilevel - Supported by the Social-Ecological Model, this framework recognizes the influence of multilevel domains of influence on reproductive health, including individual, neighborhood, health system, and societal factors (McLeroy et al., 1988McLeroy K.R. Bibeau D. Steckler A. Glanz K. An ecological perspective on health promotion programs.Health and Education Quarterly. 1988; 15: 351-377Crossref PubMed Scopus (4172) Google Scholar).•Life course health – Pregnancy outcomes like SMM are affected by life course experiences, and SMM may in turn affect subsequent life course health (Lu and Halfon, 2003Lu M.C. Halfon N. Racial and ethnic disparities in birth outcomes: A life-course perspective.Maternal and Child Health Journal. 2003; 7: 13-30Crossref PubMed Scopus (670) Google Scholar).•Intergenerational health – Historic context of one's family and society affect the reproductive health of current and subsequent generations (e.g., intergenerational trauma, slavery, genocide of Native populations) (Halfon and Hochstein, 2002Halfon N. Hochstein M. Life course health development: An integrated framework for developing health, policy, and research.Milbank Quarterly. 2002; 80 (iii): 433-479Crossref PubMed Scopus (606) Google Scholar; McLeroy et al., 1988McLeroy K.R. Bibeau D. Steckler A. Glanz K. An ecological perspective on health promotion programs.Health and Education Quarterly. 1988; 15: 351-377Crossref PubMed Scopus (4172) Google Scholar).1B. Health and racial equityGiven stark disparities by race and social disadvantage, SMM research should be centered on achieving equity, within a framework that is informed by multiple relevant movements and theories, including, for example, Critical Race Theory, EcoSocial Theory, Intersectionality, and Reproductive Justice (Black Women Scholars and the Research Working Group of the Black Mamas Matter Alliance, 2020Black Women Scholars and the Research Working Group of the Black Mamas Matter AllianceBlack maternal health research re-envisioned: Best practives for the conduct of research with, for, and by Black mamas.Harvard Law & Policy Review. 2020; 14: 393-415Google Scholar; Ford and Airhihenbuwa, 2010Ford C.L. Airhihenbuwa C.O. The public health critical race methodology: Praxis for antiracism research.Social Science Medicine. 2010; 71: 1390-1398Crossref PubMed Scopus (261) Google Scholar; Krieger, 2020Krieger N. Measures of racism, sexism, heterosexism, and gender binarism for health equity research: from structural injustice to embodied harm-an ecosocial analysis.Annual Review of Public Health. 2020; 41: 37-62Crossref PubMed Scopus (99) Google Scholar; Ross, 2017Ross L.J. Reproductive justice as intersectional feminist activism.Souls. 2017; 19: 286-314Crossref Scopus (89) Google Scholar) [see references for further explication].1C. Community-engaged researchSMM research should be guided by principles of community-engaged research, which acknowledge that contributions from people with lived experience and highest burden, at every stage of the research process, are essential to its effectiveness (Ortiz et al., 2020Ortiz K. Nash J. Shea L. Oetzel J. Garoutte J. Sanchez-Youngman S. Wallerstein N. Partnerships, processes, and outcomes: A health equity-focused scoping meta-review of community-engaged scholarship.Annual Review of Public Health. 2020; 41: 177-199Crossref PubMed Scopus (45) Google Scholar; Wang et al., 2020bWang E. Glazer K.B. Sofaer S. Balbierz A. Howell E.A. Racial and ethnic disparities in severe maternal morbidity: A qualitative study of women's experiences of peripartum care.Womens Health Issues. 2020; 31: 75-81Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar).2. Defining SMM2A. Timing of SMM•SMM indicators should characterize severe complications that arise during pregnancy or postpartum, and not situations at risk of leading to severe complications.2C. Indicators•Standardized approaches that link precursor clinical conditions with SMM events are needed to fully understand the causes of SMM, how best to approach it analytically, and how to prevent it.2C. Transparency•Research should provide a clear definition of SMM, report all codes and criteria that are used, and use existing validated indices whenever possible.•Coding experts should be included in the development and revision of SMM indices.•If transfusion is included in the definition of SMM and volume of transfusion is not available, findings should be reported with and without including transfusion as an indicator.•Research should state the timing of SMM events that are included, provide justification, and discuss potential concomitant limitations.2D. Continuum of care•When possible, research should include SMM events that arise during pregnancy or childbirth, through at least 42 days postpartum, and the approach should be clearly described.•Further research is needed that compares SMM that emerges during the prenatal, peripartum, and postpartum periods.3. Data improvements•Improve the availability of data resources that-Allow rigorous characterization of SMM-Include critical individual-level sociodemographic variables (e.g., maternal race-ethnicity, age, parity, socioeconomic status)and-Enable characterization of social and structural determinants (see Figure 2 for examples).•Some suggested strategies are as follows:-Develop state-based datasets that link vital records with maternal and infant hospital discharge records, including indicators of where people live so that social and structural determinants can be studied.-Improve the quality of maternal health information recorded in vital records. Using current versions of birth and fetal death certificates to study SMM is not recommended.-Improve the quality of social determinant information in hospital discharge records.-Fund the exploration of birthing people's and communities' perspectives and priorities regarding SMM.Abbreviation: SMM, severe maternal morbidity. Open table in a new tab Abbreviation: SMM, severe maternal morbidity. Second, research should be centered on principles of health and racial equity, which can be informed by several movements and theories (recommendation 1B). Research should be grounded in reproductive justice and an explicit acknowledgment that health-related inequities arise from social forces rather than innate biologic differences. Reproductive justice is a framework created by Black women that emphasizes the human right to maintain personal bodily autonomy, to have or not have children, and to parent one's children in safe, supportive communities (Black Women Scholars and the Research Working Group of the Black Mamas Matter Alliance, 2020Black Women Scholars and the Research Working Group of the Black Mamas Matter AllianceBlack maternal health research re-envisioned: Best practives for the conduct of research with, for, and by Black mamas.Harvard Law & Policy Review. 2020; 14: 393-415Google Scholar; Ross, 2017Ross L.J. Reproductive justice as intersectional feminist activism.Souls. 2017; 19: 286-314Crossref Scopus (89) Google Scholar). As articulated by Critical Race Theory and Krieger's EcoSocial model, disparities emanate from a historical context of bias and racism, rooted in societal power structures, that is manifested over time and across generations in multiple aspects of one's social context and living environment (e.g., social policy, health care quality, and safety) (Krieger, 2020Krieger N. Measures of racism, sexism, heterosexism, and gender binarism for health equity research: from structural injustice to embodied harm-an ecosocial analysis.Annual Review of Public Health. 2020; 41: 37-62Crossref PubMed Scopus (99) Google Scholar). The resulting exposures are embodied over the life course and ultimately lead to greater biologic vulnerability and adverse health outcomes (Roberts, 1998Roberts D. Killing the Black body: Race, reproduction, and the meaning of liberty. Pantheon, New York, NY1998Google Scholar; Krieger, 2020Krieger N. Measures of racism, sexism, heterosexism, and gender binarism for health equity research: from structural injustice to embodied harm-an ecosocial analysis.Annual Review of Public Health. 2020; 41: 37-62Crossref PubMed Scopus (99) Google Scholar). Furthermore, health equity must be acknowledged, understood, and improved along multiple intersectional dimensions, including sexual and gender identification, disability, socioeconomic status, and migrant and/or documentation status. Frameworks to guide the incorporation of these tenets into research exist and should be used (e.g., Public Health Critical Race praxis, intersectionality) (Ford and Airhihenbuwa, 2010Ford C.L. Airhihenbuwa C.O. The public health critical race methodology: Praxis for antiracism research.Social Science Medicine. 2010; 71: 1390-1398Crossref PubMed Scopus (261) Google Scholar). Third, principles of community-engaged research, which acknowledge that contributions from people who represent and directly advocate for those who have experienced SMM, and especially from groups bearing the highest burden of SMM, are essential to effective, impactful research and intervention (Wang et al., 2020bWang E. Glazer K.B. Sofaer S. Balbierz A. Howell E.A. Racial and ethnic disparities in severe maternal morbidity: A qualitative study of women's experiences of peripartum care.Womens Health Issues. 2020; 31: 75-81Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar) and are needed across all stages of the research process, from inception to dissemination (Ortiz et al., 2020Ortiz K. Nash J. Shea L. Oetzel J. Garoutte J. Sanchez-Youngman S. Wallerstein N. Partnerships, processes, and outcomes: A health equity-focused scoping meta-review of community-engaged scholarship.Annual Review of Public Health. 2020; 41: 177-199Crossref PubMed Scopus (45) Google Scholar) (recommendation 1C). Declaration and integration of these principles into study designs and dissemination, by inclusive research teams that center the voices and experiences of socially marginalized investigators and communities, will help ensure that we ask meaningful questions that yield meaningful answers and do not perpetuate racism and other forms of oppression (Boyd et al., 2020Boyd R.W. Lindo E.G. Weeks L.D. McLemore M.R. On racism: A new standard for publishing on racial health inequities. Health Affairs Blog.https://www.healthaffairs.org/do/10.1377/hblog20200630.939347/full/Date: 2020Date accessed: August 31, 2020Google Scholar; Hardeman et al., 2020Hardeman R.R. Karbeah J. Kozhimannil K.B. Applying a critical race lens to relationship-centered care in pregnancy and childbirth: An antidote to structural racism.Birth. 2020; 47: 3-7Crossref PubMed Scopus (23) Google Scholar; Julian et al., 2020Julian Z. Robles D. Whetstone S. Perritt J.B. Jackson A.V. Hardeman R.R. Scott K.A. Community-informed models of perinatal and reproductive health services provision: A justice-centered paradigm toward equity among Black birthing communities.Semin Perinatol. 2020; 44: 151267Crossref PubMed Scopus (19) Google Scholar; Vyas et al., 2020Vyas D.A. Eisenstein L.G. Jones D.S. Hidden in plain sight – Reconsidering the use of race correction in clinical algorithms.New England Journal of Medicine. 2020; 383: 874-882Crossref PubMed Scopus (396) Google Scholar). Future research should center the perspectives of those affected by SMM and implement their priorities for research and intervention (Eniola et al., 2020Eniola F. Nack A. Niles P. Morton C.H. Searing H. Women’s experiences with severe maternal morbidity in New York City: A qualitative report.https://www1.nyc.gov/assets/doh/downloads/pdf/csi/womens-experience-with-severe-maternal-morbidity-nyc-qualitative-report.pdfDate: 2020Google Scholar; Wang et al., 2020bWang E. Glazer K.B. Sofaer S. Balbierz A. Howell E.A. Racial and ethnic disparities in severe maternal morbidity: A qualitative study of women's experiences of peripartum care.Womens Health Issues. 2020; 31: 75-81Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar). In summary, SMM and its inequities should be conceptualized within a multidimensional causal chain of events framework that intentionally incorporates multiple relevant theoretical frameworks (see Table 1.) Although not every study or prevention strategy will address all of the complexities we have described, grounding in their essence will produce better research that is more likely to lead to sustainable, equitable improvement of maternal health. Another important obstacle to understanding SMM—overall and with respect to equity—is variability in how SMM is conceptually defined and operationalized or identified from data (England et al., 2020England N. Madill J. Metcalfe A. Magee L. Cooper S. Salmon C. Adhikari K. Monitoring maternal near miss/severe maternal morbidity: A systematic review of global practices.PLoS One. 2020; 15: e0233697Crossref PubMed Scopus (18) Google Scholar; Knight and Joseph, 2020Knight M. Joseph K.S. Severe maternal morbidity and maternal mortality: A need for consensus on concepts and prevention efforts.Paediatric Perinatal Epidemiology. 2020; 34: 377-378Crossref PubMed Scopus (6) Google Scholar). The American College of Obstetricians and Gynecologists defines SMM as unintended outcomes of the process of labor and delivery that have significant short-term or long-term consequences for maternal health and can be considered a near miss for maternal mortality (American College of Obstetricians, 2016Kilpatrick S.K. Ecker J.L. American College of Obstetricians and Gynecologists, the Society for Maternal-Fetal MedicineSevere maternal morbidity: Screening and review.American Journal of Obstetrics and Gynecology. 2016; 215: B17-B22Abstract Full Text Full Text PDF Scopus (106) Google Scholar). SMM cases are typically identified from a composite of SMM indicators (i.e., complications or events that qualify as SMM). For example, the Centers for Disease Control and Prevention (CDC) SMM index includes a broad array of indicators that can be obtained from International Classification of Disease (ICD) codes in hospital discharge data (CDC., 2017CDCSevere maternal morbidity in the United States.https://www.cdc.gov/reproductivehealth/maternalinfanthealth/severematernalmorbidity.html#anchor_SMMDate: 2017Date accessed: May 30, 2018Google Scholar). In contrast, the World Health Organization definition focuses on organ dysfunction criteria, which tend to require laboratory results (Say et al., 2009Say L. Souza J.P. Pattinson R.C. Maternal near miss—towards a standard tool for monitoring quality of maternal health care.Best Practice & Research: Clinical Obstetrics & Gynaecology. 2009; 23: 287-296Crossref PubMed Scopus (542) Google Scholar). Greater consensus is needed regarding processes to ascertain cases (be it from case review or administrative data) and what conditions to include, as discussed elsewhere (Knight, 2020Knight M. Defining severe maternal morbidity-When is it time to stop?.Paediatric and Perinatal Epidemiology. 2020; 34: 384-385Crossref PubMed Scopus (2) Google Scholar; Knight and Joseph, 2020Knight M. Joseph K.S. Severe maternal morbidity and maternal mortality: A need for consensus on concepts and prevention efforts.Paediatric Perinatal Epidemiology. 2020; 34: 377-378Crossref PubMed Scopus (6) Google Scholar). Here we point out some more general conceptual points that we believe are important to improving consistency and clarity in how SMM is defined. First, we recommend that SMM indicators should characterize severe complications that arise during or following pregnancy, and not conditions at risk of severe complications (recommendation 2A). In this case, preexisting conditions such as sickle-cell anemia, HIV disease, or severe obesity would not be considered SMM, but sickle-cell crisis, HIV-related complications, or acute myocardial infarction might be. This view guided the development of an SMM index by the CDC, which is used commonly in U.S. studies of SMM but has not been applied in all studies of SMM (CDC., 2017CDCSevere maternal morbidity in the United States.https://www.cdc.gov/reproductivehealth/maternalinfanthealth/severematernalmorbidity.html#anchor_SMMDate: 2017Date accessed: May 30, 2018Google Scholar; Chantry et al., 2020Chantry A.A. Berrut S. Donati S. Gissler M. Goldacre R. Knight M. Deneux-Tharaux C. Monitoring severe acute maternal morbidity across Europe: A feasibility study.Paediatric and Perinatal Epidemiology. 2020; 34: 416-426Crossref PubMed Scopus (10) Google Scholar; Dzakpasu et al., 2020Dzakpasu S. Deb-Rinker P. Arbour L. Darling E.K. Kramer M.S. Liu S. Joseph K.S. Severe maternal morbidity surveillance: Monitoring pregnant women at high risk for prolonged hospitalisation and death.Paediatric and Perinatal Epidemiology. 2020; 34: 427-439Crossref PubMed Scopus (15) Google Scholar). Second, we recommend development of standardized approaches that link precursor clinical conditions with SMM indicators (recommendation 2B). SMM-defining events may or may not directly indicate the immediate underlying clinical condition that preceded SMM. For example, major respiratory events typically identified as SMM, such as pulmonary edema or acute respiratory distress syndrome, can be caused by varied precursor clinical conditions, such as preeclampsia, infection, cardiac disease, or hemorrhage. In some cases, the connection between SMM and its proximal clinical precursor is obvious (e.g., eclampsia follows preeclampsia). Either way, determining the clinical precursor to SMM is a separate step from identifying the SMM event itself. This step requires further attention, as it will help us understand pathways leading to SMM and opportunities for prevention. Third, we recommend transparency in how SMM is defined and reported (recommendation 2C). SMM measures vary in the indicators they include, which can lead to considerable variability in prevalence estimates (England et al., 2020England N. Madill J. Metcalfe A. Magee L. Cooper S. Salmon C. Adhikari K. Monitoring maternal near miss/severe maternal morbidity: A systematic review of global practices.PLoS One. 2020; 15: e0233697Crossref PubMed Scopus (18) Google Scholar; Snowden et al., 2021Snowden J.M. Lyndon A. Kan P. El Ayadi A. Main E. Carmichael S.L. Severe maternal morbidity: A comparison of definitions and data sources.American Journal of Epidemiology. 2021; 190: 1890-1897Crossref PubMed Scopus (4) Google Scholar). The use of auxiliary factors to refine case identification, such as length of hospital stay or intensive care unit admission, also varies across studies (Snowden et al., 2021Snowden J.M. Lyndon A. Kan P. El Ayadi A. Main E. Carmichael S.L. Severe maternal morbidity: A comparison of definitions and data sources.American Journal of Epidemiology. 2021; 190: 1890-1897Crossref PubMed Scopus (4) Google Scholar). One example is blood transfusion. Transfusion is included in the CDC index, but ICD codes do not indicate transfusion volume. This lack of specificity can result in misclassification when transfusion, which may or may not qualify as “severe,” is the only SMM indicator present (Main et al., 2016Main E.K. Abreo A. McNulty J. Gilbert W. McNally C. Poeltler D. Kilpatrick S. Measuring severe maternal morbidity: Validation of potential measures.American Journal of Obstetrics and Gynecology. 2016; 214 (643 e641–643.e610)Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar); indeed, approximately half of cases have transfusion as their only indicator in studies using the CDC index. CDC thus currently reports SMM with and without including transfusion as an indicator. Inconsistency in the actual codes selected to identify indicators within similar coding systems is another problem. For example, the CDC index and the Bateman index use some different ICD codes for the same indicators (Snowden et al., 2021Snowden J.M. Lyndon A. Kan P. El Ayadi A. Main E. Carmichael S.L. Severe maternal morbidity: A comparison of definitions and data sources.American Journal of Epidemiology. 2021; 190: 1890-1897Crossref PubMed Scopus (4) Google Scholar). Even when using the same indices, variability in coding systems and their application may affect cross-study or cross-population comparison (Chantry et al., 2020Chantry A.A. Berrut S. Donati S. Gissler M. Goldacre R. Knight M. Deneux-Tharaux C. Monitoring severe acute maternal morbidity across Europe: A feasibility study.Paediatric and Perinatal Epidemiology. 2020; 34: 416-426Crossref PubMed Scopus (10) Google Scholar). To facilitate comparisons across studies, we recommend the following: detailed description of how SMM is defined; inclusion of medical coding experts in the development of SMM indices; use of existing, validated indices; and reporting of findings with and without including transfusion as an indicator. Fourth, we recommend SMM research and intervention address the continuum of care from the prenatal through postpartum periods (recommendation 2D). Clarity about SMM timing is important. SMM may emerge during pregnancy, at the time of childbirth, or postpartum. A recent review of SMM definitions reported that only about half of prior studies of SMM actually stated the range of timing of SMM-defining events (England et al., 2020England N. Madill J. Metcalfe A. Magee L. Cooper S. Salmon C. Adhikari K. Monitoring maternal near miss/severe maternal morbidity: A systematic review of global practices.PLoS One. 2020; 15: e0233697Crossref PubMed Scopus (18) Google Scholar). Most studies are limited to data from childbirth hospitalizations, which capture most but not all cases (Girsen et al., 2020Girsen A.I. Sie L. Carmichael S.L. Lee H.C. Foeller M.E. Druzin M.L. Gibbs R.S. Rate and causes of severe maternal morbidity at readmission: California births in 2008–2012.Journal of Perinatolofy. 2020; 40: 25-29Crossref PubMed Scopus (13) Google Scholar). Further complicating this matter is inconsistency in defining the length of the postpartum period, typically varying from 42 days to 1 year (Nationa