At a glance
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) |
|
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) |
|
Provides information about national trends and characteristics of pregnancy-related deaths, including pregnancy-related mortality ratios |
| State and local Maternal Mortality Review Committees (MMRCs) |
|
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 54 reporting areas (50 states, Puerto Rico, Northern Mariana Islands, 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.