Effects of Age-specific Fertility Trends on Overall Fertility Trends: United States, 1990-2023.

Objectives: This report examines the role of age-specific trends in fertility rates in the decline in the number of births and of general fertility rates (GFRs) and total fertility rates (TFRs).

Methods: Data are from the National Center for Health Statistics' National Vital Statistics System birth data files from 1990 through 2023. To estimate the role of changes in age-specific fertility rates on total births, GFRs, and TFRs from 1990 through 2023, 1990 rates for each maternal age category were kept constant and applied to all subsequent years to produce adjusted totals and rates.

Results: The actual number of U.S. births declined 14% from 1990 to 2023, the GFR declined 23%, and the TFR declined 22%. Due to declines in birth rates among females younger than age 30, holding their 1990 birth rates constant resulted in higher adjusted GFRs, TFRs, and number of births in 2023 than the actual rates and numbers. Due to increases in birth rates to women age 30 and older, holding their 1990 birth rates constant would have led to lower adjusted GFRs, TFRs, and number of births in 2023 than the actual rates and numbers. The magnitude of the decrease in birth rates among females younger than 30 was greater than the magnitude of the increase in rates among women 30 and older, resulting in declining overall fertility rates. These age-specific changes in birth rates resulted in changing maternal age distributions-in 1990, females younger than 30 accounted for 7 in 10 births (69.8%), while in 2023, they accounted for less than 1 in 2 (48.6%).

Summary: The decline in fertility rates over the past few decades results from declining rates among females younger than 30 coupled with smaller increases in rates among older women.