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Data sources

ÐÇ¿ÕÓéÀÖ¹ÙÍø requests the 54 reporting areas* (50 states, Puerto Rico, the Commonwealth of the Northern Mariana Islands, New York City, Washington, DC) voluntarily send death records for all women ages 10-60 years old who died during or within 1 year of the end of their pregnancy, regardless of the cause of death. If the death is linked to a live birth or fetal death, those records are also requested. When available, additional sources of information such as media reports and/or individual case reports are also shared with ÐÇ¿ÕÓéÀÖ¹ÙÍø by public health agencies, including jurisdiction-based maternal mortality review committees.

*Data from Puerto Rico was included in PMSS beginning in 2020, and data from the Commonwealth of the Northern Mariana Islands was included in PMSS beginning in 2021. In 2023, Washington DC was not included in PMSS.

Methods

Clinically trained medical epidemiologists review the information available to determine if each death was pregnancy-related and assign each pregnancy-related death a PMSS-identified cause of death.

A pregnancy-related death is defined as a death during or within 1 year of the end of pregnancy from any cause related to, or aggravated by, the pregnancy.

The temporal association between pregnancy status and death is ascertained from the death record based on one or more of the following: the pregnancy checkbox indicating the woman was pregnant at the time of death or describing the interval between the end of a pregnancy and death; words or codes indicating a pregnancy; notes indicating the approximate interval of complications causing, or events leading to, death. If a birth or fetal death occurred within 1 year of the mother's death, the information from those records is used to ascertain the temporal association between the death and end of pregnancy. The causal association between the pregnancy status and death is based on the clinical cause of death, the interval between the end of pregnancy and death, and the biologic processes of pregnancy complications.

Causes of death are coded based on a system first established in 1986 by the American College of Obstetricians and Gynecologists and the ÐÇ¿ÕÓéÀÖ¹ÙÍø Maternal Mortality Study Group. A 10-group cause-of-death classification including hemorrhage, infection or sepsis, amniotic fluid embolism, thrombotic pulmonary or other embolism, hypertensive disorders of pregnancy, anesthesia complications, cerebrovascular accidents, cardiomyopathy, other cardiovascular conditions, and other noncardiovascular medical conditions is used for cause-of-death reporting. Beginning with 2020 data, a new cause of death code specific for COVID-19 was added to the infection or sepsis category.

Data from PMSS are used with birth data from the National Vital Statistics System (NVSS) via ÐÇ¿ÕÓéÀÖ¹ÙÍø Wide-Ranging Online Data for Epidemiologic Research (WONDER) to calculate the pregnancy-related mortality ratio (PRMR), an estimate of the number of pregnancy-related deaths for every 100,000 live births. PRMRs are not calculated when the count is fewer than 8 because the PRMR is considered not reliable by PMSS for reporting due to instability associated with small numbers.

Definitions

Race and ethnicity

Race and ethnicity information is based on the linked birth or fetal death records, when available, and from death records when a birth record or fetal death record was unavailable. Race and Hispanic origin are reported separately on the birth, fetal, and death records; more than one race can be selected. All deaths with a notation of Hispanic origin are classified as Hispanic, regardless of race. For deaths with missing notation of Hispanic origin, race, or both, the decedent's race-ethnicity was classified as unknown. Among non-Hispanic women, those that select a single race are classified as: non-Hispanic White, non-Hispanic Black, non-Hispanic American Indian or Alaska Native (AI/AN), non-Hispanic Asian, non-Hispanic Native Hawaiian or Other Pacific Islander (NHOPI). Among non-Hispanic women, those that select a multiple race categories are classified as non-Hispanic Multiple Race.

Age at death

We use age information from the death record.

Urban Rural Classifications

Urban-rural classifications are defined by the Urban-Rural Classification Scheme for Counties. Metropolitan counties, such as large central, large fringe, medium, and small, can be considered urban. Micropolitan and noncore counties can be considered rural.

Urban-rural classifications are based on county of last residence from the death record, when available, and from the birth or fetal death record when missing or undetermined on the death record. Federal Information Processing Series (FIPS) codes were applied to each record using the resident state and county FIPS codes provided on the record by matching the decedent's resident county and/or ZIP code to its corresponding county FIPS code using the Housing and Urban Development (HUD)-United States Postal Service (USPS) ZIP and the .

Health and Human Service (HHS) Regions

HHS regions, defined by the U.S. Department of Health and Human Services as of January 2025, are based on residence at the time of death when available, and from the birth or fetal death record when missing or undetermined on the death record.