National linked files of live births and infant deaths were first produced for the 1983 birth cohort. Birth cohort linked file data are available for 1983 to 1991, and both period linked files and birth cohort linked files are available starting with 1995. National linked files do not exist for 1992 to 1994.
Mode of Collection
Record linkage of live birth and infant death data files.
The linked Birth/Infant Death data set links information from the birth certificate to information from the death certificate for each infant death in the United States. The purpose of the linkage is to provide a data set that adds the many additional variables from the birth certificate to the death certificate record to enable more detailed analyses of infant mortality patterns. The linked file is used for calculating infant mortality rates by race and ethnicity, which are more accurately measured from birth certificate data than from data on the death certificate.
The Linked Birth/Infant Death data set includes all variables on the Natality (Birth) file, such as extensive information about the pregnancy, maternal risk factors, infant characteristics, and health items at birth. Data from the Mortality file, such as cause of death and age at death are also included.
To be included in the U.S. Linked Birth/Infant Death data set, both the birth and death must have occurred in the 50 states, the District of Columbia, Puerto Rico, U.S. Virgin Islands, or Guam. Data for Puerto Rico, U.S. Virgin Islands, and Guam are shown in selected state tables, but are not included in the U.S. totals. Linked Birth/Infant Death data are not available for American Samoa and Northern Mariana Islands.
Infant mortality rates are based on infant deaths per 1,000 live births. An infant death is defined as a death before the infant's first birthday.
Linked birth/infant death data files are available in two different formats: period data 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 cases, the denominator is all births occurring in the year. For example, the 2017 period linked data set contains a numerator file that consists of all infant deaths occurring in 2017 that have been linked to their corresponding birth certificates, whether the birth occurred in 2016 or 2017. In contrast, the 2017 birth cohort linked data set contains a numerator file that consists of all infant deaths to babies born in 2017, whether the death occurred in 2017 or 2018. 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. Therefore, period linked files are used to compute infant mortality rates for Healthy People 2030.
Beginning with the 2017 period linked/birth infant death data set, NCHS has begun annual release of combined period and cohort files (i.e., the 2017 period and 2016 cohort) allowing for much timelier access to cohort files.
Record weights are used to compensate for the less than 1 percent of infant death records that could not be linked to their corresponding birth records.
Response Rates and Sample Size
For the 2017 period file, 99.6% of infant death records were successfully linked to their corresponding birth records.