Trends in Maternal Mortality and Severe Maternal Morbidity During Delivery-Related Hospitalizations in the United States, 2008 to 2021

Key Points Question What were trends of and risk factors associated with maternal mortality and severe maternal morbidity (SMM) among women giving birth in US hospitals during 2008 to 2021? Findings In this cross-sectional study of more than 11.6 million delivery-related hospitalizations, regression-adjusted in-hospital maternal delivery-related mortality per 100 000 discharges declined from 10.6 to 4.6, while the prevalence of SMM per 10 000 discharges increased from 146.8 to 179.8 during 2008 to 2021. Differences were found across racial and ethnic groups, age, mode of delivery, and comorbidities for mortality and SMM. Meaning In this study, in-hospital maternal mortality improved between 2008 and 2021 despite increases in SMM prevalence and presence of comorbidities for the overall population.


Introduction
Complications from pregnancy and childbirth are leading contributors to mortality and severe morbidities, resulting in significant burden on pregnant patients and their babies.Among developed countries, the United States has the highest maternal mortality ratio. 1 In 2019, there were 3 747 540 births in the United States, with an estimated birth rate of 11.4 per 1000 population. 2 According to US Pregnancy Mortality Surveillance System (PMSS) data, the pregnancy-related mortality ratio in the United States had increased since 1987 from 7.2 deaths per 100 000 live births to 17.3 deaths per 100 000 live births in 2017, although the trend slowed substantially after 2008. 3 Maternal mortality has been described as the "tip of the iceberg" and maternal morbidity as a larger problem, "the base." 4 For every individual who dies as a result of their pregnancy, it is estimated that 20 or 30 more experience significant lifelong complications that affect their health and well-being. 5,6Severe maternal morbidity (SMM), which the US Centers for Disease Control and Prevention (CDC) defines as "unexpected outcomes of labor and delivery that result in significant short-or long-term consequences to a woman's health," 1 has steadily increased in the United States in recent years and is estimated to affect more than 50 000 patients annually.
Causes of maternal deaths and SMM at the time of delivery are multifactorial and are not well documented. 7Measuring specific outcomes occurring during delivery and hospitalization could improve understanding of how to predict, manage, and mitigate maternal outcomes.In addition, enhanced understanding of the causes of delivery-related death and SMM can inform potential strategies to improve overall maternal health outcomes in the United States.This study aimed to provide evidence to enhance understanding of patterns, trends, and risk factors associated with delivery-related deaths and SMM in US hospitals using a large maternal sample in the hospital setting.

Study Design
This retrospective cross-sectional study was conducted to examine trends associated with deliveryrelated maternal in-hospital mortality and SMM between January 2008 and December 2021, using data from the Premier PINC AI Healthcare Database (PHD).All data were statistically deidentified and adherent to the Health Insurance Portability and Accountability Act.Based on US Title 45 Code of Federal Regulations, Part 46, this study was exempted from institutional review board approval and informed consent.The study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

Data Source
The PHD is a large, all-payer (including Medicaid), geographically diverse administrative database comprising more than 1200 US hospitals and health systems. 8This database represents approximately 25% of all US inpatient admissions.All data were validated at both facility and patient levels.[11][12][13][14][15]

Study Population
This study reviewed inpatient hospitalizations between January 1, 2008, and December 31, 2021, with any Medicare Severity Diagnosis Related Group (MS-DRG) or International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis or procedure codes (on or before September 30, 2015) or International Classification of Diseases and Related Health Problems, Tenth Revision, Clinical Modification (ICD-10-CM) codes (on or after October 1, 2015) indicating delivery (eTable 1 in Supplement 1).Hospitalizations for patients younger than 10 years at time of admission and those with evidence of abortive outcomes were excluded from the study.The index date was defined as the discharge date for the qualifying hospitalization.Missing data for categorical variables were included in the other or unknown group.Only a small percentage of patients had missing data, which should not have affected the trend analysis.

SMM
Complications or procedures indicative of SMMs were examined during the delivery-related hospitalization; these included acute myocardial infarction, acute kidney failure, amniotic fluid embolism, aneurysm, cardiac arrest or ventricular fibrillation, cardioversion, disseminated intravascular coagulation, eclampsia, heart failure or arrest during procedure, puerperal cerebrovascular disorders, acute heart failure or pulmonary edema, severe anesthesia complications, sepsis, shock, sickle cell anemia with crisis, air and thrombotic embolism, blood transfusion, hysterectomy, temporary tracheostomy, and ventilation.The diagnosis and procedure codes to identify the complications are listed in eTable 2 in Supplement 1.The presence of any SMM was used as a measure for the adverse event occurring during delivery.Morbidities were reported as number of patients with each SMM or any SMM of interest per 10 000 eligible discharges.

In-Hospital Delivery-Related Mortality
Death was defined as having delivery-related hospitalization discharge status as deceased.
In-hospital mortality was reported as the number of patients who died during index hospitalization per 100 000 eligible discharges.

Patient, Hospital, and Visit Characteristics
Patient characteristics included age (10-19, 20-24, 25-34, 35-44, Ն45 years), race and ethnicity (categorized as American Indian, Asian, Black, Hispanic, Pacific Islander, White, and other or unknown), and primary insurance payer.The other or unknown category captures all patients who selected other category for race, had missing data for race or ethnicity, or had a hospital-reported race that could not be matched to the standard race categories used in this article.Race and ethnicity were reported by the hospital.For the purposes of this study, we defined racial or ethnic minority patients as those with race or ethnicity classifications other than White.Hospital characteristics included population served (urban, rural), teaching status, US census divisions (ie, Middle Atlantic, Mountain, East North Central, East South Central, New England, Pacific, South Atlantic, West North Central, and West South Central), and hospital size (1-299, 300-499, and Ն500 beds).Visit information, such as index year, quarter (Q), admission type (elective, emergency, urgent, or trauma center), and an indicator for pre-ICD-10-CM or post-ICD-10-CM coding system change on October 1, 2015, were also examined.

Clinical Characteristics
The individual conditions in the Maternal Comorbidity Index (MCI) 16 were assessed as potential risk factors of maternal mortality or morbidity, including pulmonary hypertension, placenta previa, sickle cell disease, gestational hypertension, mild or unspecified preeclampsia, severe preeclampsia, chronic kidney disease, preexisting hypertension, chronic ischemic heart disease, congenital heart disease, systemic lupus erythematosus, HIV, multiple gestation, substance use disorder, alcohol

Statistical Analysis
Descriptive analysis was performed to assess the distribution of demographics and hospital and clinical characteristics for each year.Categorical variables were expressed as counts and percentages.
Owing to space limitations, we only included specific descriptive results for 2008, 2014 (ie, the year before the ICD-9-CM to ICD-10-CM coding change), 2016 (ie, the year after the ICD-9-CM to ICD-10-CM coding change), 2019 (ie, the year before the COVID-19 pandemic), 2020, and 2021 (ie, years during the COVID-19 pandemic), rather than for all years in this study.
Two separate multivariable logistic regression models were created to assess the independent associations of potential risk factors with delivery-related maternal mortality and SMM, adjusting for confounders.For both models, patient demographics, hospital and visit characteristics, and MCI conditions were included as covariates.In the mortality regression, the SMM complications were added to the model to account for disease conditions that happened during the delivery-related hospitalization before the occurrence of mortality.In addition, a logistic regression of mortality without SMMs as covariates was performed as a sensitivity analysis.Backward selection with P < .05 was used to select final models, with the exception that patient age, race and ethnicity, delivery type, and study year and Q were kept in the model regardless of P values.For the mortality model, SMM conditions that were closely related to each other were combined.Combined variables included bleeding complications, cardiovascular complications, respiratory complications, and an eclampsia or preeclampsia category.In the regression of SMM, eclampsia was 1 component of the SMM outcome, while the preeclampsia conditions were used as separate covariates in the model.
Adjusted mortality and SMM rates for the overall study population were calculated using recycled prediction methods 16,18 based on estimates from the regressions.Adjusted mortality and SMM rates were also reported by age group, race and ethnicity, and type of delivery, based on additional regression models that included interaction terms between year and the variable of interest.
All analyses were conducted using Python Scikit-Learn package version 0.22.1 (Python Software Foundation).Analysis of the data took place from February 2021 through March 2023.P values were 2-sided, and statistical significance was set at P < .05.

Patient Characteristics
Among the 11 628 438 eligible discharges related to delivery, more than half (6 498  Approximately one-third of the sample underwent cesarean delivery.The proportion of discharges in younger age groups decreased while the proportion in older age groups increased over the study period.The distribution of race and ethnicity, primary payer type, census region, and delivery type did not differ significantly across years (Table 1).

Maternal Comorbid Conditions
As shown in Table 1, obesity (91.0 per 1000 discharges), gestational diabetes (74.3 per 1000 discharges), and tobacco use (58.2 per 1000 discharges) were the most common comorbidities, followed by gestational hypertension, asthma, preeclampsia, preexisting hypertension, and substance use disorder.Compared with the prevalence in 2008, higher prevalence of sickle cell disease, gestational hypertension, severe preeclampsia, preexisting hypertension, substance use disorder, asthma, gestational diabetes, obesity, and hemorrhage were observed in 2021 (Table 1).

Prevalence and Trend of SMMs
The unadjusted prevalence of any SMM was estimated to be 163.1D).

Unadjusted and Adjusted Trend of In-Hospital Delivery-Related Mortality
As shown in Figure 2A 2B).A decreasing trend for in-hospital mortality was observed in all racial and ethnic groups.In particular, the greatest decrease in adjusted mortality was observed for American Indian patients: from 34.8 per 100 000 discharges in Q1 of 2008 to 2.7 per 100 000 discharges in Q4 of 2021 (Figure 2C; the 95% CI for mortality among American Indian patients is provided in eTable 4 in Supplement 1).In-hospital mortality consistently decreased during the study period for patients with cesarean delivery (from 12.6 per 100 000 discharges in Q1 of 2008 to 5.2 per 100 000 discharges in Q4 of 2021) and also for patients with vaginal delivery (from 6.6 per 100 000 discharges in Q1 of 2008 to 3.0 per 100 000 discharges in Q4 of 2021) (Figure 2D).

Risk Factors for In-Hospital Mortality and SMM
Compared with patients aged 25 to 34 years, those between 35 and 44 years had higher odds of dying during the index hospitalization (aOR, 1.49; 95% CI, 1.22-1.84).Although the association between race and mortality was not statistically significant in the regression in which SMMs were included as covariates, a sensitivity analysis showed that American Indian (aOR, 1.93, 95% CI,

Discussion
This cross-sectional study examined rates of delivery-related in-hospital maternal mortality and SMM in a large national inpatient database.In this sample encompassing more than 11 million inpatient discharges, delivery-related in-hospital mortality was found to decrease significantly over a period of 14 years.The adjusted mortality per 100 000 discharges decreased by more than 50% from Q1 of 2008 to Q4 of 2021, likely demonstrating the impact of national strategies focused on improving the maternal quality of care provided by the hospitals during delivery-related hospitalizations.In contrast, the rates of overall SMM increased over time for the overall population, which may be attributable to preexisting conditions and the increasing trend in the age of delivering patients in the past decade.The increasing trend of adjusted SMM rates was seen in all racial and ethnic minority groups and was most prominent in Asian, American Indian, and Pacific Islander patients.The fact that many of the comorbid conditions are risk factors for mortality and SMM indicates that it is essential to consider comorbid conditions when assessing SMM and mortality and that better management of patients' comorbid conditions during pregnancy may help reduce SMM occurrence and ultimately decrease mortality risk.Further improvement in patient outcomes could be achieved if patients with known risk factors could access improved care during pregnancy and during hospital delivery.

JAMA Network Open | Obstetrics and Gynecology
Maternal Mortality and Severe Maternal Morbidity in the United States, 2008-2021

Figure 2 .
Figure 2. Trend of Unadjusted and Regression-Adjusted In-Hospital Mortality Among Hospital Inpatient Discharges for Newborn Delivery, 2008 to 2021, Overall and by Age Group, Race and Ethnicity, and Delivery Type

Table 1 .
Maternal Mortality and Severe Maternal Morbidity in the United States, 2008-2021 Demographic and Clinical Characteristics of Hospital Inpatient Discharges for Newborn Delivery From 2008 to 2021 Maternal Mortality and Severe Maternal Morbidity in the United States, 2008-2021 (Table2).There was an increase in mortality from Q2 of 2020 through Q4 of 2021 that may be associated with the COVID-19 pandemic.However, after controlling for COVID-19 diagnosis, the adjusted trend decreased consistently across the full study period.The downward trend for in-hospital mortality was observed in all age groups, with the biggest decrease occurring in patients JAMA Network Open | Obstetrics and Gynecology JAMA Network Open.2023;6(6):e2317641.doi:10.1001/jamanetworkopen.2023.17641(Reprinted) June 22, 2023 6/16 Downloaded From: https://jamanetwork.com/ on 09/30/2023

Table 1 .
Demographic and Clinical Characteristics of Hospital Inpatient Discharges for Newborn Delivery From 2008 to 2021 (continued) Figure 1.Trend of Unadjusted and Regression-Adjusted Severe Maternal Morbidity (SMM) Rates Among Hospital Inpatient Discharges for Newborn Delivery, 2008 to 2021, Overall and by Age Group, Race and Ethnicity, and Delivery Type

Table 2 .
Estimates From the Multivariable Logistic Regression of In-Hospital Mortality and Any SMM Among Hospital Inpatient Discharges for Newborn Delivery, 2008 to 2021 (continued) Overall, 728 deaths among 11 628 380 inpatient hospitalizations were included in the analysis; 58 patients reported by hospitals with in-hospital mortality followed by readmission were excluded from the regression of mortality.Additional covariates included in the regression of mortality are described in the Statistical Analysis section.A total of 189 908 discharges with SMM (of 11 628 438 inpatient hospitalizations) were included in the analysis.Additional covariates included in the regression of severe maternal morbidity are described in the Statistical Analysis section.Respiratory complications included acute respiratory distress syndrome, temporary tracheostomy and ventilation as defined by the US Centers for Disease Control and Prevention.Cardiovascular complications included any of the following severe maternal morbidities: acute myocardial infarction, cardiac arrest or ventricular fibrillation, conversion of cardiac rhythm, heart failure or arrest during surgery or procedure, and pulmonary edema or acute heart failure as defined by the US Centers for Disease Control and Prevention.