Frequently Asked Questions

How NCHS Measures Maternal Deaths

What is the definition of a maternal death?

The World Health Organization (WHO) defines as a maternal death as:

• The death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from accidental or incidental causes.

The National Center for Health Statistics (NCHS) uses the WHO definition of a maternal death to determine the number of maternal deaths per 100,000 live births. This statistic is the national maternal mortality rate.

Where does NCHS obtain data for preparing maternal mortality statistics for the U.S.?

NCHS uses data from death certificates to produce statistics on maternal mortality.  This information is collected by vital records offices in the 50 states and the District of Columbia. Deaths are reported to vital records offices. Those offices review, edit, process, and register the records, and prepare mortality data files. States send a standard set of demographic and cause of death data to NCHS to produce the nation’s official death statistics.

What information from the death certificate is used by NCHS to identify maternal deaths?

NCHS uses cause-of-death information and information from a pregnancy checkbox on the death certificate to identify maternal deaths. The cause of death is determined by the certifier – the physician, medical examiner, coroner, or other authorized person who reports the information on the death certificate. Certifiers use their best medical judgement based on the information available and their expertise to determine the cause of death. The certifier also reports pregnancy status at the time of death based on a pregnancy question in the form of a checkbox item. This question asks:

IF FEMALE:

• Not pregnant within past year
• Pregnant at time of death
• Not pregnant, but pregnant within 42 days of death
• Not pregnant, but pregnant 43 days to 1 year before death
• Unknown if pregnant within the past year

These responses align with the concepts and codes in the International Classification of Disease (ICD) system that is used to collect and classify death data. The tenth revision of ICD (ICD–10) recommends including questions whether the deceased was pregnant within the year before the death to help identify maternal deaths.

Are deaths due to suicides, homicides, or accidental causes counted as maternal deaths when they occur among pregnant or recently pregnant women?

NCHS uses the WHO definition of a maternal death to count maternal deaths. WHO’s definition of a maternal death excludes deaths due to causes such as intentional and unintentional injury, poisoning (including drug overdose), and complications of medical or surgical care. Deaths from these causes are never counted as maternal deaths even if the death appears to have been related to the pregnancy, such as a motor vehicle accident resulting in a placental abruption or a suicide involving a woman suffering from postpartum depression.

Why are other causes that may not seem directly related to pregnancy, such as cancer, counted as maternal deaths?

The WHO definition of a maternal death includes deaths that are indirectly related to pregnancy such as when the pregnancy affects the development or treatment of the disease or condition that causes death, or when the disease or condition affects the pregnancy. For example, women with cancer during pregnancy may receive delayed or reduced cancer treatment, or may have pregnancy complications that are related to the cancer. Deaths among these women would be counted as maternal deaths.

Are deaths occurring 43 days through 1 year following pregnancy counted as maternal deaths?

No, they are counted as late maternal deaths. Late maternal deaths are not included in the calculation of maternal mortality rates.

Data Quality

What is the history of the pregnancy checkbox?

Studies conducted before the pregnancy checkbox was implemented found that as many as half of all maternal deaths could not be identified through cause of death information provided on death certificates. At that time, medical certifiers often did not provide enough information to indicate that a person was pregnant at the time of death or recently pregnant before death. To improve identification of deaths associated with pregnancy, the U.S. Standard Certificate of Death was revised in 2003 to include a checkbox for collecting information about pregnancy status in the year before death. While the standard certificate was revised in 2003, the revised certificate was not fully implemented in all states until 2018.

How did the addition of the checkbox impact data comparability?

The addition of the pregnancy checkbox improved the identification of maternal deaths, which resulted in a significant and disruptive break in the comparability of data collected before and after the checkbox was added. Therefore, NCHS does not recommend using NVSS data to compare maternal mortality rates before and after addition of the checkbox.

Also, states adopted the revised death certificate, which included the pregnancy checkbox, at different times during the period 2003-2017. Because maternal death information was not captured in a consistent way across states, NCHS does not recommend using NVSS data to examine trends in maternal deaths during this transition period.

How did addition of the pregnancy checkbox impact data quality?

The pregnancy checkbox was added to improve the identification of maternal deaths, which it did. However, evaluations conducted by NCHS and other researchers found that medical certifiers sometimes mark the checkbox incorrectly, resulting in an overcount of maternal deaths. In addition, there is evidence that some maternal deaths are still being missed.

NCHS evaluations also found that checkbox errors increase with maternal age. More than half of all checkbox errors occur on death certificates of women over the age of 45. In response, NCHS made changes to coding rules and reporting to ensure that when the deceased is 45 years old or older, only death certificates that mention pregnancy or a pregnancy-related condition in the reported cause of death fields are coded as maternal deaths, regardless of how the pregnancy checkbox is marked.

Where can I find more information on changes associated with the addition of the pregnancy checkbox?

Detailed information on changes to data collection methods, coding, and data files and resources, as well as reports about maternal mortality, is available here.

What is NCHS doing now to minimize pregnancy checkbox errors?

NCHS is always working to ensure completeness and accuracy of all death certificate information by:

• Providing training and tools to help medical certifiers, including online courses to improve cause-of-death reporting and a quick reference guide available as a Cause of Death mobile app.
• Offering death certificate reporting guidance to help certifiers complete the cause-of-death section on the death certificate.
• Monitoring the quality of the data with ongoing review of death certificates as they are received and following up with state vital records offices to verify information and correct inaccuracies.

For maternal mortality data, NCHS:

• Made changes to the coding process to reduce errors in statistical data.
• Provides death certificate guidance for medical certifiers that is specific to pregnancy mortality.
• Requires state vital records offices to:
• Verify pregnancy checkbox information on records containing questionable information.
• Routinely link a subset of maternal death records with birth and fetal death records to assist in identifying checkbox errors.

More Information on Maternal Mortality Data

Where can I find more information on maternal mortality data available from NCHS?

NCHS makes maternal mortality data and other information available through published reports, public and restricted use data files, and other resources. These include:

• Annual reports of maternal mortality data and reports about recent maternal mortality rates.
• Public-use and restricted-use data files that contain full information from the death certificate, giving researchers flexibility to make choices on how to analyze and track maternal mortality.
  • Additional data files were released for the transitional period when the pregnancy checkbox was implemented.
• A dashboard that presents provisional maternal mortality rates for 12-month periods. The dashboard includes the overall rate, as well as rates by race and Hispanic origin and maternal age. It is updated quarterly.
• CDC WONDER, a data query system providing mortality data that are updated on a weekly basis. Users can select variables of interest to run analyses.
• State-level data are periodically posted on the NCHS website, and are also available through CDC WONDER, and in restricted-use data files. Due to the relatively small number of maternal deaths occurring in some states, NCHS advises reading accompanying notes to understand limitations and qualifications in making comparisons across states.