Quarterly Provisional Estimates – Technical Notes – Natality, Quarter 2, 2024

Nature and sources of data

Provisional estimates are based on all complete birth records received and processed by the National Center for Health Statistics (NCHS) as of a specified cutoff date. National provisional estimates include events occurring to U.S. residents within the 50 states and District of Columbia. NCHS receives the birth records and monthly provisional occurrence counts from state vital registration systems through the Vital Statistics Cooperative Program. Provisional quarterly estimates are compared with final data when available (1,2).

Table I shows the percent completeness of the provisional data by month for the United States and each jurisdiction based on where the births occurred. The percent completeness is obtained by dividing the number of complete records from each state for each month by the corresponding provisional (expected) count and multiplying by 100.

Selected estimates are presented by race and Hispanic origin of the mother. Hispanic origin and race are reported separately on the birth certificate. Estimates shown by Hispanic origin include all persons of Hispanic origin regardless of race. Estimates for non-Hispanic persons are shown separately for each single-race group. Data by race are based on the revised standards issued by the Office of Management and Budget in 1997 (3). Estimates are shown for single-race Black non-Hispanic; single-race White non-Hispanic and Hispanic women (1). Data for additional race and ethnicity groups are available in the National Vital Statistics System natality files but were not included in these provisional estimates due to small counts and statistical unreliability of estimates for these groups.

Population denominators

Population estimates used for computing rates are postcensal estimates, which originate from the U.S. Census Bureau and are based on the 2020 Census, Vintage 2020 estimates for April 1, 2020 and 2020 Demographic Analysis estimates (4,5). Changes in rates between years in part reflect differences between vintages of the population estimates. Rates are based on the midyear population estimate (i.e., month) of the 12-month-ending period.

Computing rates

Birth rates are calculated on an annual basis per 1,000 estimated population within specified age groups. The general fertility rate refers to the total number of births per 1,000 women aged 15-44. Birth rates for women aged 50 and over have historically been too small to compute reliable age-specific birth rates. Consistent with other reports, birth rates to women aged 45 and over are computed by including all births to women aged 45 and over in the numerator, while the denominator includes population estimates of women aged 45-49 years (2,6).

Other rates (e.g., preterm birth rates, term birth rates, cesarean delivery rates) are presented as per 100 births. Estimates of birth rates at 42 weeks gestation or later (post-term) are not presented due to the small number of births in this group.

Accuracy of estimates

Provisional estimates are subject to some nonrandom sampling error. The quarterly provisional estimates are based on data that are potentially more incomplete for the most recent months. No imputations of births have been performed, because it is assumed that the data are missing at random (i.e., the degree of missing data is unrelated to estimates of reproductive health). Estimates of completion rates by month were all above 95% for the United States. However, certain states may have more delayed reporting, and it is unknown whether indicators of reproductive health may be different for these states compared with states having complete reporting. Even if no differential delay occurred, some sampling error would still exist for rate estimates, because they are based on incomplete data. A guideline for the size of this sampling error is given by deriving the variation that would occur if the data were missing at random (7); standard errors for birth rates have been calculated according to these methods, accounting for sampling error.

Partly because of the factors discussed above, provisional estimates of birth rates are rarely higher than the true rate. Historically, provisional estimates of birth rates track closely with estimates based on final data (2). Based on simulations of various levels of data completeness, ranging from 50% through 90%, estimates of the indicators included in this release can be expected to be within 1-2% of the estimates based on complete data. Exceptions were noted for birth rates among women aged 10-14 and 45 and over under scenarios where data completeness was 80% or lower. For these two age groups, the percent differences between estimates based on complete data and those based on various levels of incomplete data were larger than 1% because the birth rates are lows (0.2 and 0.9 per 1,000, respectively). However, the absolute differences between the rates across various levels of data completeness was approximately 0.1 for each age group. For example, estimated birth rates for females aged 10–14 under various levels of completeness ranged from 0.2 through 0.3 per 1,000, while those for women aged 45 and over ranged from 0.8 through 0.9 per 1,000. Notably, these simulations assumed data were missing at random.

Because the timeliness of birth reporting has been improving, accuracy of the estimates may change over time. As a result, estimates for previous quarters may change with the addition of updated data. Estimates may differ from previously published preliminary data due to rounding or the use of updated population estimates.

Interpretation of changes over time

Unless otherwise specified, a difference in age-specific birth rates is reported only if statistically significant at the 0.05 level by the test given in reference 6. That test uses a variance estimate that includes both the random fluctuation in the true number of births and the random sampling error. Similarly, differences in percentages (e.g., cesarean delivery and preterm birth) between the most recent quarter and the same quarter of the preceding year are reported only if statistically significant at the 0.05 level according to methods outlined in reference 6.

Acknowledgement

The interactive dashboard was designed by Anthony Lipphardt.

References

1. 1. 1. National Center for Health Statistics. Vital statistics data available online. Birth data files. Hyattsville, MD: National Center for Health Statistics. Available from: https://www.cdc.gov/nchs/data_access/VitalStatsOnline.htm.
      2. Osterman, MJK, Hamilton BE, Martin JA, Driscoll AK, Valenzuela CP. Births: Final data for 2022 National vital statistics reports; vol. 73 no 2. Hyattsville, MD: National Center for Health Statistics. April 2024. DOI: https://www.cdc.gov/nchs/data/nvsr/nvsr73/nvsr73-02.pdf
      3. Office of Management and Budget. Revisions to the standard for the classification of federal data on race and ethnicity. Fed Regist 62(210):58782-90. 1997.
      4. U.S. Census Bureau. Population Division. Monthly national population estimates by age, sex, race, and Hispanic origin for the United States: April 1, 2020 to December 1, 2023 (with short-term projections to December 2024). Available from: https://www2.census.gov/programs-surveys/popest/technical-documentation/file-layouts/2020-2023/NC-EST2023-ALLDATA.pdf.
      5. U.S. Census Bureau. Population Division. Monthly national population estimates by age, sex, race, Hispanic origin, and population universe for the United States: April 1, 2020 to July 1, 2023 (with short-term projections to December 2024). (NC-EST2023-ALLDATA). Monthly postcensal resident population. 2024. Available from: https://www.census.gov/data/datasets/time-series/demo/popest/2020s-national-detail.html.
      6. National Center for Health Statistics. User guide to the 2010 natality public-use file. Hyattsville, MD.
      7. Hamilton BE, Martin JA, Ventura SJ. Births: Preliminary data for 2005. National vital statistics reports; vol 55 no 11. Hyattsville, MD: National Center for Health Statistics. 2006.