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National Vital Statistics System (NVSS)

National Center for Health Statistics (NCHS)

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Overview

NVSS collects and publishes official national statistics on births, deaths, and, before 1996, marriages and divorces occurring in the United States, based on U.S. standard certificates. The vital statistics files—Birth, Fetal Death, Period Linked Birth/Infant Death, and Mortality Multiple Cause-of-Death—are detailed as follows.

Coverage

NVSS collects and presents U.S. resident data for all 50 states, New York City, and the District of Columbia (D.C.), as well as for each state, D.C., and the U.S. territories of American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and U.S. Virgin Islands. Vital events occurring in the United States to non-U.S. residents and vital events occurring abroad to U.S. residents are excluded.

Methodology

NCHS’s Division of Vital Statistics obtains information on births and deaths from the registration offices of each of the 50 states, New York City, D.C., American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and U.S. Virgin Islands. Until 1972, NCHS processed microfilm copies of all death certificates and a 50% sample of birth certificates received from all registration areas. In 1972, some states began sending their data to NCHS through the Cooperative Health Statistics System (CHSS). States that participated in the CHSS program processed 100% of their death and birth records and sent the entire data file to NCHS on computer tapes. Currently, data are sent to NCHS following procedures similar to those under CHSS. The number of participating states grew from 6 in 1972 to 46 in 1984. Starting in 1985, all 50 states and D.C. participate in the Vital Statistics Cooperative Program.

U.S. Standard Certificates of Live Birth and Death Reports are revised periodically, allowing evaluation and the addition, modification, and deletion of items. Beginning with 1989, revised standard certificates replaced the 1978 versions. The 1989 revision of the death certificate included items on educational attainment and Hispanic origin of decedents, as well as changes to improve the medical certification of cause of death. Standard certificates recommended by NCHS are modified in each registration area to serve the area’s needs. However, most certificates conform closely in content and arrangement to the standard certificate, and all certificates contain a minimum data set specified by NCHS. The 2003 revision of vital records was implemented by some states and territories beginning in 2003. The revision was fully implemented in all states and D.C. and was achieved in 2016 for birth data and 2018 for death data. The 2003 revision of the birth and death certificates included changes in the determination of multiple races and education level, among others

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Fetal Death Data Set

Overview

In Health, United States, data are presented for fetal deaths at 20 weeks or more. The Fetal Death Data Set includes characteristics of the fetus, such as sex, birthweight, and weeks of gestation; demographic information about the mother, such as age, race, Hispanic origin, and live-birth order; and medical and health information of the mother, such as maternal diabetes and hypertension.

Coverage

Data presented in Health, United States are based on reporting from all 50 states and D.C. Data for Puerto Rico, U.S. Virgin Islands, Guam, American Samoa, and Northern Marianas are not included in U.S. totals but may be included in the fetal death user’s guides and in periodic reports, available from the Vital Statistics Online Data Portal.

Methodology

State laws require the reporting of fetal deaths, and federal law mandates national collection and publication of fetal death data (P. L. 93-353). States and reporting areas submit fetal mortality data to NCHS as part of a cooperative agreement. Standard forms and procedures for the collection of the data are developed and recommended for state use through cooperative activities of the states and NCHS. NCHS shares the costs incurred by the states in providing vital statistics data for national use.

In addition to fetal mortality rates, perinatal mortality rates are also presented in Health, United States. Perinatal mortality includes both late fetal deaths (at least 28 weeks of gestation) and early infant (neonatal) deaths (within 7 days of birth). Data on early infant deaths come from the Linked Birth/Infant Death Data Set.

Issues Affecting Interpretation

Reporting requirements for fetal deaths vary by state, and these differences have important implications for comparisons of fetal mortality rates by state. The majority of states require reporting of fetal deaths at 20 weeks of gestation or more, or a minimum of 350 grams birthweight (roughly equal to 20 weeks), or some combination of the two. In 2021, 6 states required reporting of fetal deaths at all periods of gestation, 2 states at 12 weeks of gestation, and 1 state beginning at 16 weeks of gestation.

Starting with 2014 data, the obstetric estimate of gestation at delivery (OE) is used to determine gestational age, instead of the date of last normal menses (LMP), which was used for earlier years. The adoption of OE for gestational age had no or very little impact on total fetal mortality rates. However, late fetal mortality rates based on the OE were lower than those based on the LMP. For more information, see “User Guide to the 2017 Fetal Death Public Use File.”

There is substantial evidence that not all fetal deaths for which reporting is required are, in fact, reported. Underreporting of fetal deaths is most likely to occur in the earlier part of the required reporting period for each state. For example, in 2021, for those states requiring reporting of fetal deaths at all periods of gestation, 54.4% of fetal deaths at 20 weeks or more of gestation were at 20–27 weeks, whereas for states requiring reporting of fetal deaths at 20 weeks or more of gestation or 350 grams or more, 50.9% were at 20–27 weeks, indicating possible underreporting of early fetal deaths in some states.

References

For more information, see the NCHS Fetal Deaths website.

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Linked Birth/Infant Death Data Set

Overview

National linked files of live births and infant deaths are the primary data set for analyzing U.S. infant mortality trends and characteristics related to birth. It is also the preferred source for examining infant mortality by race and Hispanic origin. The Linked Birth/Infant Death Data Set includes all infant deaths reported on death certificates that can be linked to their corresponding birth certificates. The purpose of the linkage is to use the many additional variables from the birth certificate, including the more accurate race and ethnicity data, for more detailed analyses of infant mortality patterns. The Linked Birth/Infant Death Data Set includes all variables on the birth file, including race and Hispanic origin, birthweight, and maternal smoking, as well as variables on the mortality file, including cause of death and age at death.

Coverage

To be included in the U.S. linked file, both the birth and death must have occurred in the 50 states, D.C., Puerto Rico, or Guam. Linked birth/infant death data are not available for American Samoa, Northern Marianas, or U.S. Virgin Islands. Data presented in Health, United States are based on reporting from all 50 states and D.C.

Methodology

Infant deaths are defined as a death before the infant’s first birthday. In 2021, 98.9% of infant death records were linked to their corresponding birth certificates. The linkage makes available extensive information from the birth certificate about the pregnancy, maternal risk factors, infant characteristics, and health items at birth that can be used for more detailed analyses of infant mortality. The linked file is the preferred source for calculating infant mortality rates by race and Hispanic origin, because this information is more accurately measured from the birth certificate, where race and Hispanic origin are self-reported by the mother or family members. Infant mortality rates by race and Hispanic origin calculated using the mortality file are based on information from the death certificate, which is reported by the funeral director as provided by an informant (often the surviving next of kin), or in the absence of an informant, on the basis of observation. For information about the reporting of race and Hispanic origin, see Sources and Definitions, Hispanic origin; Race.

Starting with 1995 data, linked birth/infant death data files are available for period and birth cohort data. The numerator for the period linked file consists of all infant deaths occurring in a given data year linked to their corresponding birth certificates, whether the birth occurred in that year or the previous year. The numerator for the birth cohort linked file consists of deaths to infants born in a given year. In both formats, the denominator is all births occurring in the year. For example, the 2019 period linked file contains a numerator file that consists of all infant deaths occurring in 2019 that have been linked to their corresponding birth certificates, whether the birth occurred in 2018 or 2019. In contrast, the 2019 birth cohort linked file will contain a numerator file that consists of all infant deaths to babies born in 2019, whether the death occurred in 2019 or 2020. Although the birth cohort format has methodological advantages, it creates substantial delays in data availability, because it is necessary to wait until the close of the following data year to include all infant deaths in the birth cohort. Starting with 1995 data, period linked files are used for infant mortality rate data sets in Health, United States. Other changes to the data set starting with 1995 include the addition of record weights to compensate for the 1%–2% of infant death records that could not be linked to their corresponding birth records.

Issues Affecting Interpretation

Period linked file data starting with 1995 are not strictly comparable with birth cohort data for 1983–1991. Denominators for infant mortality rates are based on the number of live births, rather than on population estimates. For information about the reporting of race and Hispanic origin or reporting area changes for the birth certificate items, see Sources and Definitions, Age; Hispanic origin; Race.

References

For more information, see the NCHS Linked Birth/Infant Death Data website.

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