Pregnancy Mortality Surveillance System

What to know

The Centers for Disease Control and Prevention (CDC) conducts national surveillance to better understand the causes of pregnancy-related deaths. The Pregnancy Mortality Surveillance System (PMSS) defines a pregnancy-related death as a death during or within 1 year of the end of pregnancy from any cause related to or aggravated by the pregnancy. Medical epidemiologists review and analyze applicable vital records, and additional available data from all 50 states, New York City, and Washington, DC. Beginning in 2020, data from Puerto Rico is included in PMSS.

Pregnancy Mortality Surveillance System logo with icon of pregnant woman

Pregnancy-related deaths data

Figure 1. Pregnancy-related mortality ratio in the United States: 1987-2020

Data from PMSS and birth records from the National Vital Statistics System (NVSS) via CDC Wide-Ranging Online Data for Epidemiologic Research (WONDER) are used to calculate the pregnancy-related mortality ratio (PRMR), an estimate of the number of pregnancy-related deaths for every 100,000 live births.

Since PMSS was implemented, the number of reported pregnancy-related deaths in the United States increased from 7.2 deaths per 100,000 live births in 1987 to 24.9 deaths per 100,000 live births in 2020. The graph above shows PRMRs between 1987 and 2020 (the latest available year of data).

Pregnancy-related deaths by race-ethnicity

Considerable racial-ethnic disparities in pregnancy-related mortality exist,12 and these disparities increased during 2020.

Figure 2. Pregnancy-related mortality ratio by race-ethnicity: 2017–2019 and 2020a,b

In 2017–2019, the highest PRMR was among non-Hispanic Native Hawaiian or Other Pacific Islander persons. In 2020, the highest PRMR was among non-Hispanic American Indian or Alaska Native persons. Variability in the risk of death by race-ethnicity may be due to several factors including access to care, quality of care, prevalence of chronic diseases, structural racism, and implicit biases.345

Causes of pregnancy-related deaths

Figure 3. Causes of pregnancy-related deaths in the United States: 2017–2019 and 2020a

Spotlight‎

Infection was the most frequent underlying cause of pregnancy-related deaths in 2020, driven by pregnancy-related COVID-19 deaths.

A new cause of death code was used during PMSS review of deaths occurring in 2020 specific for COVID-19, within the infection category. Infection became the most frequent underlying cause of death (27.5%) and COVID-19 accounted for 14.7% of all pregnancy-related deaths in 2020.

Approximately half (55%) of the increased number (n = 243) of pregnancy-related deaths between 2019 and 2020 had an underlying cause of COVID-19.

Pregnant and postpartum persons are more likely to get very sick from COVID-19 compared to those who are not pregnant.67 In addition, studies show that an increasing number of pregnant persons in the United States have chronic health conditions such as hypertension,89 diabetes,910 and chronic heart disease.11 These conditions may put a person at higher risk of complications during or within 1 year of the end of pregnancy.

Pregnancy-related deaths by urban-rural classifications

Figure 4. Pregnancy-related mortality ratio by urban-rural classificationsa: 2017–2019 and 2020b

Spotlight‎

In 2020, the highest pregnancy-related mortality ratio persisted among people residing in the most rural classification.

Figure 4 shows PRMRs per 100,000 live births by urban-rural classifications using the 2013 National Center for Health Statistics Urban-Rural Classification Scheme for Counties. Data were geocoded using the Texas A&M Geoservices' Batch Geocoding. Metropolitan counties, such as large central, large fringe, medium, and small, can be considered urban. Micropolitan and noncore counties can be considered rural.

A prior study found that PRMRs were higher in noncore (the most rural categorization) counties when compared to metropolitan counties.12 Variability in the risk of death by geographic location groups might reflect chronic health conditions and access to care, including risk-appropriate care.1314  For example, residents of rural areas may face challenges such as distance from and lack of access to obstetric services and providers.

Frequently asked questions

What are the sources of maternal mortality estimates?

For estimates of maternal mortality at the national level, there are two main information systems: the National Vital Statistics System (NVSS) and the Pregnancy Mortality Surveillance System (PMSS). NVSS provides information on maternal deaths in the United States. NVSS includes only includes deaths during and up to 42 days after the end of pregnancy. PMSS, which began in 1987, provides information on pregnancy-related deaths, which includes deaths during pregnancy and up to a year after the end of pregnancy. For estimates of maternal mortality at the state and local level, maternal mortality review committees (MMRCs) provide state and local level information about pregnancy-related deaths.

We cannot directly compare information from NVSS, PMSS, and MMRCs. While they are all trusted sources of maternal mortality information, they are based on different data, and they serve different purposes.a

Comparison of Maternal Mortality Information Systems
Information System Based on Purpose
National Vital Statistics System (NVSS) 
  • Death records
To assign International Classification of Diseases (ICD) codes, which identify maternal deaths, among deaths that occurred during pregnancy and up to 42 days after		 Provides information about national trends and characteristics of maternal deaths, including maternal mortality rates

Cause of death coding that aligns with the World Health Organization definition of a maternal death
Pregnancy Mortality Surveillance System (PMSS) 
  • Death records
  • Any linked birth records or fetal death records
To review and determine pregnancy-relatedness among deaths during pregnancy and up to 1 year after 		Provides information about national trends and characteristics of pregnancy-related deaths, including pregnancy-related mortality ratios
State and local Maternal Mortality Review Committees (MMRCs) 
  • Death records
  • Any linked birth records or fetal death records
  • Medical records
  • Social service records
  • Autopsies
  • Informant interviews
To review deaths, determine pregnancy-relatedness, and identify prevention recommendations within the state and local context among deaths during pregnancy and up to 1 year after 		Provides information about pregnancy-related deaths at the state or local level, and can be combined across jurisdictions

Pinpoints specific factors contributing to deaths

Determines if deaths are preventable

Provides actionable prevention recommendations
a Trost SL, Beauregard J, Petersen EE, et al. Identifying deaths during and after pregnancy: new approaches to a perennial challenge. Public Health Rep. 2023;138(4):567–572. 

How have changes in data identification over time impacted trends in pregnancy-related mortality ratios?

The magnitude of the overall increase in pregnancy-related mortality over time is unclear. Identification of pregnancy-related deaths has improved over time due to:

  • Use of computerized data linkages between death records and birth and fetal death records by states.
  • Changes in the way causes of death are coded.
  • Addition of a pregnancy checkbox to death records.

Errors in reported pregnancy status on death records have been described, however, potentially leading to the overestimation of the number of pregnancy-related deaths.

How do PMSS data differ from MMRC data?

Maternal mortality review is a process by which a multidisciplinary committee at the state or local level identifies and reviews deaths that occur during or within 1 year of the end of pregnancy. MMRCs have access to multiple sources of information that can provide a deeper understanding of the circumstances surrounding a death than PMSS. State and local MMRCs perform comprehensive reviews of deaths using information beyond what is available in vital records, including medical and nonmedical data sources. MMRCs have the potential to get the most detailed, complete data on maternal mortality that then supports their ability to make actionable prevention recommendations. This also allows MMRCs to make determinations of pregnancy-relatedness on a broader set of deaths than is possible for PMSS, such as deaths due to injury.

How are PMSS data collected and coded?

CDC requests the 53 reporting areas (50 states, Puerto Rico, New York City, Washington, DC) voluntarily send copies of death records for all women who died during or within 1 year of the end of pregnancy, linked live birth or fetal death records if applicable, and any additional data when available. All of the information obtained is summarized, and medical epidemiologists determine the cause of death and whether the death was pregnancy-related. Causes of death are coded based on a system first established in 1986 by the American College of Obstetricians and Gynecologists and the CDC Maternal Mortality Study Group.

How are PMSS data used?

Data are analyzed by CDC scientists. Information about causes of pregnancy-related deaths and risk factors associated with these deaths is released periodically through peer-reviewed literature, CDC's Morbidity and Mortality Weekly Reports, and the CDC website. These reports support the interpretation and uptake of information among clinicians and public health practitioners.

How are PMSS data confidentiality protected?

PMSS data, including data received from reporting areas, are protected under 308(d) Assurances of Confidentiality. Because of this assurance, all data and documents are considered confidential materials and are safeguarded to the greatest extent possible.

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Content Source:
National Center for Chronic Disease Prevention and Health Promotion (NCCDPHP); Division of Reproductive Health
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