CDC initiated national surveillance of pregnancy-related deaths in 1986 because more clinical information was needed to fill data gaps about causes of maternal death. The first year of data reporting was 1987. //

In PMSS, a pregnancy-related death is defined as the death of a woman while pregnant or within 1 year of the end of pregnancy regardless of the outcome, duration, or site of the pregnancy — from any cause related to or aggravated by the pregnancy or its management. Pregnancy-related deaths as defined in PMSS generally do not include deaths due to injury. //

CDC’s National Center for Health Statistics’ National Vital Statistics System (NVSS) reports the national maternal mortality rate: the number of maternal deaths per 100,000 live births. A maternal death is defined as a death while pregnant or within 42 days of the end of pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from accidental or incidental causes. This definition and timeframe are consistent with that used by the World Health Organization for reporting on maternal mortality rates. NVSS uses two pieces of information on the death record to identify maternal deaths — the pregnancy checkbox and the certified recording of the cause of death to assign maternal mortality ICD-10 codes. Identification of maternal deaths using automated processing of death records alone relies upon the death certifier accurately reporting causes of death related to pregnancy and pregnancy status. More information on NVSS maternal mortality coding is available.

Like NVSS, PMSS uses vital records for identification of deaths, including descriptions of causes of death and pregnancy status information on death records. Different from NVSS, PMSS further uses linkages of death records of women of reproductive age to birth and fetal death records within 1 year of the death, media searches, and reporting from public health agencies, health care providers and the public in the identification process. PMSS uses a time frame that includes deaths during pregnancy through 1 year after the end of pregnancy; this timeline allows evaluation of all deaths which might be pregnancy-related. In PMSS, deaths are reviewed by medical epidemiologists who perform an in-depth review of vital records and other data as available (e.g., medical records, autopsy reports) for each death to determine the pregnancy-related mortality ratio. These linkage and review processes by PMSS result in slower reporting than NVSS, but a more rigorous identification of deaths related to pregnancy.