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Severe maternal morbidity

Severe maternal morbidity
Literature review current through: Jan 2024.
This topic last updated: Nov 06, 2023.

INTRODUCTION — Severe maternal morbidity (SMM) is variously defined but generally refers to health-impacting and life-threatening events that occur during hospitalization for childbirth. It may precede or be associated with maternal mortality and is more common: there are approximately 70 cases of SMM for each maternal death in the United States [1]. Clinicians, researchers, governmental organizations, and other stakeholders in obstetric health care delivery use SMM as an indicator of potential systems issues that can be addressed to improve patient outcomes. In a statewide SMM review in Illinois, 22 percent of SMM cases were considered potentially preventable, and another 20 percent were deemed not preventable but improvement in care was needed [2].

Evaluation of SMM is limited by the absence of a reliable and reproducible means of collecting data and the rarity of many complications. In order to capture as many events as possible, large or national datasets, such as the National Inpatient Sample (NIS) in the United States, are promising resources as there is already a system for data collection in place. The NIS uses International Classification of Diseases discharge information, which includes up to 40 diagnostic and 25 procedural codes per patient from a sample of 20 percent of United States community hospitals and represents approximately seven million hospitalizations annually. The State Inpatient Databases (SID) include inpatient discharge records from community hospitals from all payer sources (eg, private insurance, Medicare, Medicaid, uninsured) in a particular state. Data in the SID are abstracted from these discharge records and include clinical information, such as diagnoses and procedures, as well as nonclinical details, such as patient demographics, charges, and length of stay.

This topic will provide an overview of SMM, including initiatives to reduce its rate. Maternal mortality is reviewed separately. (See "Overview of maternal mortality" and "Approaches to reduction of maternal mortality in resource-limited settings".)

DEFINITIONS FROM INTERNATIONAL AND NATIONAL ORGANIZATIONS — While there is no consensus on a single definition of, or approach to, SMM, various stakeholders, such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO), have developed processes to help standardize the approach to learning more about life-threatening and health-impacting events surrounding childbirth.

World Health Organization — The WHO defines SMM as "potentially life-threatening conditions" and proposes a comprehensive approach to the review of maternal care in order to capture all relevant events [3].

In 2011, WHO published a proposal for a systematic approach for evaluating the quality of obstetric care and monitoring the impact of interventions in health care delivery. Many of the definitions used in this proposal were derived from the proceedings of a 2007 working group composed of obstetricians, midwives, epidemiologists, and public health professionals. This group conceptualized a "near miss," a term borrowed from the airline industry, as either defined by a specific disease entity (eg, preeclampsia), a specific intervention (eg, blood transfusion), or by a measure of organ dysfunction (eg, serum lactate >5 mmol/L) [3,4].

The proposed list of clinical, laboratory, and management-based criteria for a maternal near miss is listed in the table (table 1).

In addition, to assess quality of care, data are captured in the following categories. The qualifying criteria for each of these categories are listed in the table (table 2).

Severe maternal complications.

Critical interventions (ie, those required in the management of life-threatening or potentially life-threatening conditions or intensive care unit [ICU] use).

Maternal near-miss cases (ie, patients who survived organ dysfunction that was life-threatening).

Maternal vital status (ie, maternal mortality).

For the purposes of this assessment, the authors restricted the definition of severe maternal complications to severe postpartum hemorrhage, severe preeclampsia or eclampsia, sepsis or severe systemic infection, uterine rupture, and severe complications of abortion, whereas the category of life-threatening conditions captured evidence of deranged physiology without emphasis on the precipitating cause [5].

The implementation of this assessment requires an operational plan to ensure detailed record keeping, timely and accurate data entry, and the capacity to perform ongoing systematic review. The stated intention of this approach is to provide a local health care delivery system with a means to understand patterns in maternal morbidity and mortality, the use of interventions, and impact of changes in care delivery. However, it has limitations, such as the additional time and personnel, and may not be feasible to implement in all settings. Another example is when patients receive care during pregnancy and the postpartum period from different care systems. This can result in a gap in ascertainment of data and highlights the relative strength of proposed regional programs for assessment and the advantages of national data systems.

Centers for Disease Control and Prevention — The CDC defines SMM as unexpected outcomes of labor and delivery that result in significant short- or long-term consequences to the individual's health [6]. They have developed a comprehensive list of 21 adverse maternal health events indicative of SMM and their corresponding International Classification of Diseases, 10th revision (ICD-10) diagnostic and procedural codes (table 3), reflecting their decision to use administrative hospital discharge data for surveillance of SMM [7].

There are advantages and disadvantages to using administrative databases to capture maternal morbidity statistics. By operationalizing the definition of SMM using diagnostic and procedural codes, the CDC facilitates analysis of trends over time for these relatively uncommon events and analysis of associations between SMM and other risk factors or outcomes. The use of a defined group of codes is convenient because these codes are universal among health care delivery systems in the United States.

On the other hand, coding may be incomplete or inaccurate. Diagnostic codes are intended primarily for billing purposes and do not necessarily reflect the clinical details of a delivery hospitalization [8]. This concern was addressed in a validation study comparing older ICD-9 criteria with information from patient chart review [9]. The authors reported that the ICD-9 had sensitivity of 77 percent and positive predictive value of 44 percent for identifying SMM in their cohort of patients from California. Another concern with this approach is that recognition of outcomes related to labor and delivery may not occur during the delivery hospitalization: Complications may be diagnosed in the outpatient setting or during a hospital readmission and, therefore, not captured unless linked to a delivery episode. In a United States study, approximately 15 percent of SMM cases developed de novo in the six weeks, and usually in the two weeks, after delivery hospitalization [10].

American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine — The American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) published a consensus statement in 2016 outlining recommendations for screening and review of cases of SMM [11]. Their intention was to propose guidelines for delivery facilities to implement in order to systematically improve patient care. However, they acknowledged that neither organization has agreed upon a comprehensive definition of SMM and not all cases that meet criteria for review will be determined to be preventable.

Regardless of the definition used, ACOG and SMFM recommend that all facilities:

Establish a screening process to detect cases of SMM. Recommended screening criteria for SMM are transfusion of ≥4 units of blood and peripartum ICU admission; individual institutions may choose additional criteria.

Review all cases that meet screening criteria with the intent of determining whether the morbidity could have been avoided and whether there is an opportunity for system change and improvement.

In-depth review makes it possible to identify potential systems issues that might have contributed to morbidity for screen-positive cases that occur as a result of various circumstances. For example, controlled transfusion may be performed in a patient with a complicated surgery versus an unanticipated postpartum hemorrhage, or ICU admission may be planned for monitoring of a patient with a cardiac condition versus emergency for a patient with hemorrhagic stroke. While this approach facilitates local review of practices, it may limit understanding of the broader epidemiologic patterns of maternal morbidity. As an example, case ascertainment may vary according to local practices (eg, thresholds for transfusion, availability of intensivist services on labor and delivery units versus the ICU).

UK Obstetric Surveillance System — The UK Obstetric Surveillance System (UKOSS) is a database designed to support epidemiologic research of rare conditions of pregnancy, including morbidity events. On a monthly basis, UKOSS sends a survey containing a list of conditions under surveillance to a representative at each hospital with an obstetric facility. When cases are identified, more detailed information is requested about each case. UKOSS also collects data on a control group of pregnant people without the specified conditions.

The list of conditions changes as studies are completed and applications for new studies are accepted. For example, ongoing surveillance in 2019 included amniotic fluid embolism, peripartum hyponatremia, extremely preterm prelabor rupture of membranes, and any pregnancy complicated by diabetic ketoacidosis, cirrhosis, previous Fontan procedure, or antithrombin/protein C deficiency [12]. The list of completed studies appears in the table (table 4).

UKOSS covers a wide spectrum of questions about antenatal, peripartum, and postpartum care. By establishing a system for data collection across multiple institutions, rare conditions and events can be studied. The scope of the data collection system at any given point in time facilitates chart level abstraction, which may improve the accuracy of data. However, because the process is not automated, data for the same conditions are not tracked over time, and longitudinal changes may not be seen.

INCIDENCE

United States

Overall rates — In the United States, the overall rate of SMM increased from 49.5 per 10,000 delivery hospitalizations in 1993 to 144.0 per 10,000 delivery hospitalizations in 2014 [13], and then fell to 139.7 per 10,000 delivery hospitalizations from 2016 to 2017 [14]. The increase through 2014 was mostly driven by blood transfusions, which increased from 24.5 to 122.3 per 10,000 delivery hospitalizations over the same interval, particularly after 1998 to 1999 [13]. If blood transfusions are excluded, the rate of SMM increased by approximately 20 percent, from 28.6 in 1993 to 35.0 in 2014. These figures are based on International Classification of Diseases, 9th revision (ICD-9) coding (which included 25 indicators). In 2015, ICD-10 coding with 21 indicators was introduced. Using the new system, SMM was 72.0 per 10,000 delivery hospitalizations in 2016 (excluding blood transfusion) and was essentially stable for two years before increasing in 2018 and peaking at 79.7 per 10,000 delivery hospitalizations in 2019 [15].

It should be noted that the risk for SMM extends beyond delivery hospitalization, with as many as 15 percent of new cases occurring in the six weeks following initial discharge [10].

Specific morbidities — Blood transfusion is by far the major contributor to the increase in SMM in recent decades (figure 1). Between 1993 and 2014, the overall rate of SMM increased from 49.5 to 144.0 per 10,000 delivery hospitalizations (190 percent increase); however, when blood transfusions are excluded, the rate only increased from 28.6 to 35.0 per 10,000 delivery hospitalizations (22 percent increase). Accordingly, over this same time period, blood transfusions increased from 24.5 to 122.3 per 10,000 deliveries (400 percent increase) [16].

Most other Centers for Disease Control and Prevention SMM indicators also increased but by much less. Rates of acute myocardial infarction or aneurysm, acute kidney failure, adult respiratory distress syndrome, cardiac arrest, fibrillation, conversion of cardiac rhythm, shock, ventilation/temporary tracheostomy, sepsis, and hysterectomy increased by ≥50 percent. Rates of disseminated intravascular coagulation (DIC) and air and thrombotic embolism increased by <50 percent. The rate of amniotic fluid embolism remained unchanged. Rates of acute congestive heart failure or arrest during surgery or procedure, eclampsia, and severe anesthesia complications decreased [17,18]. A subsequent study of the national rate of SMM from 2012 to 2019 reported a 15 percent increase overall, with the largest individual increases attributable to acute kidney failure (up 139 percent) and sepsis (up 155 percent) [15]. These increases were not substantially associated with transition to ICD-10, but several other indicators did have changes associated with transition. For example, DIC decreased by 33 percent, largely associated with ICD-10 changes. Smaller magnitude changes attributable to the ICD-10 transition included decreases for severe anesthesia complications and heart failure during surgery, and increases in air and thrombotic embolism and pulmonary edema/acute heart failure.

The Healthcare Cost and Utilization Project Statistical Brief presented similar findings using data from the State Inpatient Databases during the period from 2006 to 2015: the rate of deliveries involving blood transfusion increased by 54 percent while the rate of deliveries involving all of the other 20 SMM indicators increased by 24 percent [17]. Interestingly, over a similar time period in Canada, the rate of hemorrhage requiring hysterectomy increased from 2.6 to 4.6 per 10,000 deliveries, while the rate of hemorrhage requiring transfusion decreased from 12.7 to 6.3 per 10,000 deliveries [19]. It is unclear the extent to which prevailing practices in management of hemorrhage (eg, published thresholds for transfusion, guidelines on the management of obstetric hemorrhage, etc) influence the reported rates of this common obstetric complication.

International

Resource-abundant countries — In resource-abundant countries, SMM statistics can be collected from diagnostic and procedural codes generated from delivery and/or postpartum admissions. However, comparison of SMM incidence remains limited, primarily by the lack of a consistent definition, but also by differences in methodology [20]. Despite the differences in the definition of SMM, resource-abundant countries have reported increases in many of the less common SMM indicators analyzed, such as myocardial infarction, pulmonary edema, and mechanical ventilation, as in the United States [19].

For example:

A survey performed in Scotland defined SMM by disease (eg, eclampsia, cardiac arrest) and organ system criteria (eg, acute kidney dysfunction, acute respiratory dysfunction) and reported 3.8 cases per 1000 births [21]. A population-based study in the Netherlands defined SMM by disease (eg, uterine rupture, eclampsia) and management criteria (eg, intensive care unit admission) and reported 7.1 cases per 1000 births [22]. Even though both studies included major obstetric hemorrhage in the definition, this was considered a transfusion of ≥5 units in the Scottish study and ≥4 units in the Dutch study, a difference in terms that largely accounted for the differences in incidence [20-22].

Studies conducted in Canada, Finland, and Australia have used similar methodologies, relying on administrative data to describe the incidence of SMM. However, the specific diagnostic and procedural codes chosen differ, making direct comparison challenging (table 5). Furthermore, the inclusion criteria for diagnostic and procedural codes in each of these studies differ. For example, the criteria in the Canadian study were near-miss conditions with the potential to cause maternal death that were reliably recorded (ie, not obviously subject to coding error), whereas in the Finnish study, the inclusion criteria were conditions "indicating a severe maternal complication" that were not necessarily subject to validation. SMM rates of 4.38 and 7.60 per 1000 births were reported in Canada and Finland, respectively [19,23].

In Australia, data are collected and analyzed on a state level as a result of the structure of public health care in that country [24]. The Victorian Perinatal Data Collection database is a population-based surveillance system that records maternal and neonatal information to track morbidities statewide. The Australian Maternal Morbidity Outcome Indicator is a composite of diagnostic and procedural ICD codes that has been validated as a definition of SMM. In a 2015 analysis, the prevalence was 5.3 per 1000 births [25].

Resource-limited countries — In comparison, in resource-limited countries, near-miss criteria examined at a local level may provide the best insight into SMM [26-31]. Reported rates of SMM range from 5.06 in Baghdad, Iraq, to 25.4 per 1000 deliveries in the Madang Province of Papua New Guinea; the latter has one of the highest maternal mortality rates in the world [26-31].

In resource-limited countries, hemorrhage is the leading cause of maternal near-miss cases [26-31]. While trends in specific indicators over time are not as readily available for resource-limited countries, other leading causes of maternal near-miss cases in recent analyses include hypertensive disorders of pregnancy and infection [26-32].

RISK FACTORS — Internationally, risk factors for SMM seem to vary by availability of resources and the structure of the health care system. Data are available on the following risk factors.

Maternal age — In the United States, SMM is increased in patients under age 20 years, then falls to a nadir in the 20-to-29 year age group, and then increases with age 30 to 39 years, with the highest rates among patients ages 40 years and older (196.0, 131.2, 134.5, and 246.0 per 10,000 delivery hospitalizations, respectively [14]) [14,17,33,34]. This increased risk has been shown to extend into the postpartum period [35]. A similar association between maternal age and increasing risk for SMM has been reported in other resource-abundant countries [25].

In resource-limited countries, age >30 has been associated with maternal near-miss cases [26,28].

Racial and ethnic minorities — Racial and ethnic minority status appears to be an important risk factor consistently associated with SMM. Lifelong exposure to systemic racism and discrimination may account for the increased risk of SMM in minority individuals [36]. Failure to rescue from SMM is a major factor in the excess maternal mortality of racial and ethnic minority individuals in the US [37].

In the United States, SMM incidence appears to be highest among non-Hispanic Black individuals and lowest among non-Hispanic White individuals (225.7 versus 104.7 per 10,000 delivery hospitalizations [14]) [17,33,38-42]. It has been suggested that disparity among races and ethnicities in the United States is related to increased use of blood transfusions among racial and ethnic minorities compared with use in non-Hispanic White individuals, but even when patients with blood transfusions as the only criterion for SMM are excluded, non-Hispanic Black individuals have a higher rate of SMM than non-Hispanic White individuals (74.2 versus 33.4 per 10,000 delivery hospitalizations) [14]. The risk of SMM has also been shown to differ among subgroups of the Asian and Pacific Islander community, ranging from 94 cases per 10,000 births among Korean patients to 165 cases per 10,000 births among Filipina patients [43]. The largest racial and ethnic disparities in SMM in the United States have been noted among those with multiple chronic conditions.

Similarly, in the United Kingdom, the odds of SMM are 83 percent higher for Black African individuals than for White European individuals [44]. Higher rates of SMM have also been noted for Black Caribbean, Bangladeshi, Pakistani, and other non-White, non-Asian individuals.

In an Australian study from Victoria, SMM was higher in aboriginal and African individuals [25,45].

Discontinuity of hospital care — Fragmentation of care, defined as being admitted to a different hospital for postpartum care than where birth occurred, has been associated with an increased risk for SMM [46].

Lower socioeconomic status — Lower socioeconomic status may be a risk factor for SMM among pregnant people in the United States and other countries [14,25,41]. One study looking at the extent to which socioeconomic status modified the effect of race and ethnicity on SMM among pregnant people in New York City determined that racial differences persisted across all socioeconomic groupings, and living in the poorest neighborhoods further increased the risk for SMM among Black non-Latin American and Latin American individuals [41]. However, other studies have not found an association between socioeconomic status and SMM in the United States [47].

Medical comorbidities — Studies in Canada, Australia, and the United States have reported an association between preexisting conditions and risk for SMM [14,19,25]. The risk for SMM increases with an increasing number of comorbidities (in multivariable regressions, adjusted ORs for 1, 2, or ≥3 comorbidities were 4.4, 6.6, and 9.1, respectively) [14,48]. In one analysis that described a dose-response relationship between the number of comorbid conditions and the risk for SMM, 45 percent of Black patients in the study had at least one comorbid condition compared with 33 percent of White patients, 32 percent of Hispanic patients, and 28 percent of Asian patients [14]. Efforts to improve comparison of SMM events have focused on expanding comorbidity scores used in these analyses [49].

Various studies have explored the association between specific preexisting medical conditions and SMM [50-58]. Further research is needed to explore the differences between potentially modifiable conditions (eg, anemia) and non-modifiable conditions (eg, congenital heart disease).

An association between high gestational weight gain and SMM has been reported [59]. A study from the United States noted that pregnant people who had gestational weight gain in excess of National Academy of Medicine (formerly the Institute of Medicine [IOM]) guidelines were at increased risk of SMM compared with those who met weight gain target ranges, although the absolute increase in SMM was small (for 1 to 19 pounds above and ≥20 pounds above target ranges, the increase in SMM was 2.1 and 6.0 cases per 1000 deliveries, respectively) [60].

The COVID-19 pandemic prompted examination of the association between COVID-19 infection and maternal complications [61,62]. Of patients requiring hospitalization for COVID-19 during pregnancy, the literature suggests that approximately 10 percent required intensive care unit level of care, with use of mechanical ventilation in approximately 8 percent [63]. Pregnancy in the setting of at least one medical comorbidity has been associated with increased risk for maternal morbidity and mortality [64-67].

Interpregnancy interval — In a study including over 14,000 patients with SMM, both short (<6 months) and long (≥60 months) interpregnancy intervals were significantly, but modestly, associated with SMM [68]. After excluding transfusion from SMM, long IPI was still associated with SMM but short IPI was not a factor. Interpretation of findings was limited by a lack of within-mother analysis. (See "Interpregnancy interval: Optimizing time between pregnancies", section on 'Limitations of available data'.)

Stillbirth — Delivery of a stillborn is associated with an increased risk for SMM, particularly among pregnant people with preexisting medical conditions [69]. In resource-limited countries, anemia and a history of stillbirth have been associated with increased risk for SMM [26,31].

Cesarean birth — Cesarean birth, either in the index pregnancy or in a prior pregnancy, is associated with higher rates of SMM [23,25,33]. Patients who undergo cesarean birth in the very early preterm period may be at further increased risk for SMM [70].

In a study that evaluated SMM by mode of birth and risk factors (maternal age, medical comorbidity [obesity, preeclampsia, diabetes]), attempted vaginal birth was associated with lower risk for SMM for patients with each risk factor except for preeclampsia; patients with preeclampsia had a similar risk for SMM with planned cesarean and planned vaginal birth [71].

Successful assisted vaginal delivery has been associated with a lower risk for SMM when compared with cesarean birth, however, failed assisted vaginal birth has been associated with an increased risk for SMM [72].

Previous SMM — In a population-based study, the risk of SMM at the second birth was threefold higher in patients with SMM in their first birth than in those without a prior SMM (65.2 versus 20.3 per 1000 in patients; adjusted relative risk 3.11, 95% CI 2.96-3.27) [73].

NEONATAL OUTCOMES — In a population-based cohort study from Canada, maternal morbidity was associated with a higher risk of infant death [74]. Infant mortality occurred in 8.9 per 1000 live births with SMM versus 2.8 per 1000 live births without SMM. One observation from this study was the concurrent presence of maternal and neonatal sepsis.

LONG-TERM HEALTH OUTCOMES — There are few data regarding the long-term health outcomes of individuals who experience SMM. An increased risk for postpartum psychiatric morbidity and substance use disorder has been described [75,76]. There is also evidence that patients who experience SMM may have an accelerated risk for mortality [77].

PREVENTION

Scoring systems — Efforts to reduce SMM have largely focused on systematic evaluation of inpatient data that represent an abnormality in normal physiology. These data were used to create tools for early identification of patients at risk for SMM. For example:

The Maternal Early Warning System, Maternal Early Obstetric Warning Scores, and Maternal Early Warning Trigger are sets of thresholds for abnormal vital signs (termed maternal early warning criteria [MEWC]) that should trigger a bedside patient evaluation [78-80]. The thresholds and possible causes for the abnormalities are shown in the tables (table 6 and table 7).

The obstetric comorbidity index (OB-CMI) is a comorbidity-based screening tool for identifying patients who are at risk of SMM while on the labor and delivery unit [81]. In a prospective cohort, the frequency of SMM increased from 0.4 percent for patients with a score of 0/15 to 19 percent for those with a score ≥9/15 [81].

Another SMM prediction tool uses a risk scoring tool based on antepartum, intrapartum, or combined risk factors to predict SMM [82]. In a prospective cohort, an antepartum score >5 points had sensitivity and specificity of 60 and 65 percent, respectively; an intrapartum score ≥2 had sensitivity and specificity of 68 and 78 percent, respectively; and a combined score ≥5 had sensitivity and specificity of 62 and 98 percent.

Use of such tools has been associated with decreased rates of SMM [83-86]. The California Maternal Quality Care Collaborative (CMQCC) uses statewide data to develop and continuously improve quality improvement toolkits focused on life-threatening obstetric complications such as hemorrhage and preeclampsia.

There is some evidence that a modified version of a scoring system may be appropriate in resource-limited settings [87]. At least one study examined a device that measures heart rate and blood pressure, calculates a shock index (heart rate divided by systolic blood pressure), and alerts the provider using a traffic light system (red, amber, green) reflecting previously validated shock index thresholds [88]. This helps to quickly identify patients at risk of compromise and who may need transfer to a facility with a higher level of care.

Standardized review of SMM — Some states have implemented a review of cases of SMM in order to identify opportunities for improvement. This review facilitates examination of social, systems, and clinical issues related to SMM [2].

Bundles — A "bundle" is a collection of checklists, protocols, and educational materials derived from evidence-based interventions with the goal of reducing a specific morbidity [89]. The Safe Motherhood Initiative from the American College of Obstetricians and Gynecologists District II has developed bundles for hypertension, hemorrhage, and venous thromboembolism [90]. There is some evidence that such bundles have been effective in reducing SMM [91,92].

Patient care — At the patient-provider level, providers should evaluate patients for factors that may impact the outcome of pregnancy and counsel them appropriately (table 8) [93]. This risk assessment should be started before pregnancy, repeated at the first prenatal visit and during the course of pregnancy, and again postpartum and between pregnancies [36].

Prevention and treatment of chronic conditions among females of childbearing age may also reduce SMM [14]. Individuals with medical or obstetric comorbid conditions may benefit from early consultation with a maternal-fetal medicine specialist to create a management plan, including the most appropriate location for delivery [48].

UpToDate topics address identification and management of common causes of SMM. For example:

(See "Overview of postpartum hemorrhage" and "Postpartum hemorrhage: Medical and minimally invasive management" and "Postpartum hemorrhage: Management approaches requiring laparotomy".)

(See "Preeclampsia: Clinical features and diagnosis" and "Preeclampsia: Antepartum management and timing of delivery" and "HELLP syndrome (hemolysis, elevated liver enzymes, and low platelets)" and "Eclampsia".)

(See "Sepsis syndromes in adults: Epidemiology, definitions, clinical presentation, diagnosis, and prognosis" and "Evaluation and management of suspected sepsis and septic shock in adults".)

(See "Uterine rupture: After previous cesarean birth" and "Uterine rupture: Unscarred uterus".)

(See "Placenta accreta spectrum: Clinical features, diagnosis, and potential consequences" and "Placenta accreta spectrum: Management".)

(See "Disseminated intravascular coagulation (DIC) during pregnancy: Clinical findings, etiology, and diagnosis".)

(See "Deep vein thrombosis in pregnancy: Epidemiology, pathogenesis, and diagnosis" and "Venous thromboembolism in pregnancy and postpartum: Treatment" and "Venous thromboembolism in pregnancy: Prevention".)

(See "Acute respiratory failure during pregnancy and the peripartum period".)

(See "Acquired heart disease and pregnancy" and "Pregnancy in women with congenital heart disease: General principles" and "Pregnancy and valve disease".)

(See "Pregnancy and contraception in patients with nondialysis chronic kidney disease" and "Pregnancy in patients on dialysis".)

SUMMARY AND RECOMMENDATIONS

Definition – There is no single definition of severe maternal morbidity (SMM). Approaches to collecting data about SMM include analysis of existing data from diagnostic and billing databases as well as chart-level review based on screening criteria. There are advantages and disadvantages to each approach. (See 'Definitions from international and national organizations' above.)

The World Health Organization has proposed a system for assessing the quality of maternal care, taking into consideration severe maternal complications, critical interventions, maternal near-miss cases, and maternal mortality (table 2). (See 'World Health Organization' above.)

The Centers for Disease Control and Prevention has compiled a list of indicators of SMM that includes various diagnoses that reflect organ dysfunction (table 3). (See 'Centers for Disease Control and Prevention' above.)

The American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine recommend that health care systems establish a screening process to detect cases of SMM, starting with cases including transfusion of ≥4 units of blood or admission to the intensive care unit, and review all cases that meet screening criteria with attention to opportunities for system improvement. (See 'American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine' above.)

Prevalence – SMM has increased over the last few decades in resource-rich countries (figure 1). Obstetric hemorrhage remains the leading cause in both resource-rich and resource-limited countries. (See 'Incidence' above.)

Risk factors – Risk factors for SMM include younger or older age, racial and ethnic minority status, lower socioeconomic status, medical comorbidities, and cesarean delivery. (See 'Risk factors' above.)

Prevention

Efforts to reduce SMM have focused on early identification and systematic evaluation of inpatient data that represent an abnormality in normal physiology. The Maternal Early Warning System, Maternal Early Obstetric Warning Scores, and Maternal Early Warning Trigger are sets of thresholds for abnormal vital signs that trigger a bedside evaluation of the patient (table 6 and table 7). (See 'Scoring systems' above.)

A "bundle" is a collection of checklists, protocols, and educational materials derived from evidence-based interventions with the goal of reducing a specific morbidity. The Safe Motherhood Initiative has developed bundles for hypertension, hemorrhage, and venous thromboembolism. (See 'Bundles' above.)

At the patient-provider level, providers should evaluate patients for factors that may impact the outcome of pregnancy and counsel them appropriately (table 8). This risk assessment should be started before pregnancy, repeated at the first prenatal visit and during the course of pregnancy, and again postpartum and between pregnancies. (See 'Patient care' above.)

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