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U.S. Fertility Rates Continue Decline; Age of Mothers Shifts

Maternal age distribution shifts dramatically as overall birth rates continue a 30-year decline, with women younger than 30 now accounting for less than half of all births, and an increase of older mothers.

Conexiant

U.S. fertility rates have continued their decades-long decline from 1990 to 2023, with significant shifts in the age distribution of mothers, researchers reported in a new comprehensive analysis.

The findings were published by the National Center for Health Statistics in National Vital Statistics Reports. Authors documented how declining birth rates among women younger than 30 are driving the overall trend, despite increases in births among women 30 and older.

Key Findings

Between 1990 and 2023, total U.S. births declined 14% (from 4,158,212 to 3,596,017). The general fertility rate (GFR) declined 23% (from 70.9 to 54.5 births per 1,000 females aged 15–44). The total fertility rate (TFR) also declined, by 22% (from 2.08 to 1.62 births per woman), and fell from near replacement level (2.1) to well below it.

The researchers employed a novel methodological approach to isolate the impact of age-specific fertility trends by applying 1990 fertility rates to subsequent years' population structures.

"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," they noted.

Age-Specific Changes

The study documented dramatic changes in birth rates across different age groups:

  • Births to females younger than 20 declined 73% from 1990 to 2023, representing 390,740 fewer births

  • Women aged 20–24 experienced a 44% decline during that time frame (476,760 fewer births)

  • Women aged 25–29 saw a 23% decline (290,541 fewer births)

  • Women aged 30–34 had a 24% increase (211,989 more births)

  • Women aged 35–39 experienced a 90% increase (287,048 more births)

  • Women 40 and older had a 193% increase (96,809 more births).

These shifts have fundamentally altered the age distribution of U.S. births. In 1990, women under 30 accounted for nearly 70% of all births; by 2023, they represented less than half (48.6%).

Impact Analysis

Through counterfactual analysis, the researchers demonstrated that if 1990 birth rates for women under 30 had remained constant, the adjusted 2023 GFRs would have been 9% to 17% higher than the actual rate. Conversely, if 1990 birth rates for women 30 and older had remained constant, the adjusted 2023 GFRs would have been 2% to 7% lower than the actual rate.

"If birth rates for females younger than 30 had not declined from their 1990 levels, GFRs, TFRs, and the number of births in 2023 would have been higher," the authors explained. "Conversely, if birth rates for women 30 and older had not risen from their 1990 levels, the result would have been 85,000 to 251,000 fewer births in 2023 as well as lower GFRs and TFRs."

Age-Specific Birth Rate Changes

The report details significant changes in age-specific birth rates:

  • For females aged 10 to 14: 86% decrease (from 1.4 to 0.2 births per 1,000)

  • For females aged 15 to 19: 78% decrease (from 59.9 to 13.1)

  • For women aged 20 to 24: 51% decrease (from 116.5 to 57.7)

  • For women aged 25 to 29: 24% decrease (from 120.2 to 91.0)

  • For women aged 30 to 34: 17% increase (from 80.8 to 94.3)

  • For women aged 35 to 39: 71% increase (from 31.7 to 54.3)

  • For women aged 40 to 44: 127% increase (from 5.5 to 12.5)

  • For women 45 and older: 450% increase (from 0.2 to 1.1).

The authors acknowledged the limitations of their analytical approach: "To illustrate the effect of trends in age-specific rates on overall fertility trends, note that these analyses rely on the creation of hypothetical fertility trends. In particular, holding the birth rates of younger women constant does not account for how a birth, or its absence, might affect subsequent fertility at older ages," they wrote.

The observed patterns reflect both postponed and foregone fertility, the authors concluded, noting that "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."

Disclosures were not made available at the time of publishing.