This database report counts of live births occurring within the United States by state, county, child's gender and weight, mother's race, mother's age, mother's education, gestation period, and prenatal care.  Births to nonresidents of the United States are excluded from all tabulations by place of residence. Data are derived from birth certificates. Counties with fewer than 100,000 persons are combined together under the label "Unidentified Counties."  For confidentiality reasons, totals of 1-5 in counties are suppressed.  Data are not available for all counties. 

Single race categories include: All Races, American Indian or Alaska Native, Asian, Black or African American, More than one race, Native Hawaiian or Other Pacific Islander, White, Not Available, and Unknown or Not Stated.  Bridged race categories include All Races, American Indian or Alaska Native, Asian or Pacific Islander, Black or African American, White, and Not Reported.

Changes in demographic category classifications in 2010 make some birth and fertility rates comparisions inconsistent with earlier years.  Users should exercise caution when comparing time series data across races and/or ethnicities because of this change. 

Note that some states, including California, ceased reporting the mother's age and marital status, e.g., Mothers 25-29, Unmarried, Mothers 25-29, Married, etc. in 2017.  Instead, while states still report the mother's age, they report marital status as unknown or not available.  

See additional documentation from the CDC for changes in some variables over time.