A new provisional report from the Centers for Disease Control finds that the United States had the lowest number of births since 1979 and the lowest fertility rate in our nation’s history.

According to the report, the number of births for the United States in 2020 was 3,605,201, down 4% from 2019. This is the sixth consecutive year that the number of births has declined after an increase in 2014.

The general fertility rate reached another record low for the United States. The general fertility rate was 55.8 births per 1,000 women aged 15–44, down 4% from 2019. The total fertility rate was 1,637.5 births per 1,000 women in 2020, down 4% from 2019 to also reach another record low. This puts the total fertility rate at below the replacement rate.

In 2020, birth rates declined for women in all age groups 15–44 and were unchanged for adolescents aged 10–14 and women aged 45–49. The birth rate for teenagers aged 15–19 declined by 8% in 2020 to 15.3 births per 1,000 females; rates declined for both younger (aged 15–17) and older (aged 18–19) teenagers. 

The cesarean delivery rate rose to 31.8% in 2020; the low-risk cesarean delivery rate increased to 25.9%. The preterm birth rate declined to 10.09% in 2020, the first decline in the rate since 2014.

What is “fertility rate”?

Several different metrics are used to measure the “fertility rate.” The most common uses of the term refer to:

• General fertility rate (GFR): This metric is the number of births per 1,000 women of childbearing age (i.e., aged 15–44). It measures the number of live births in a particular year.
• Total fertility rate (TFR): This metric refers to the total number of children who have been born or are likely to be born to a woman in her lifetime if she were subject to the prevailing rate of age-specific fertility in the population. 
• Age-Specific Fertility Rate (ASFR): This metric is the number of live births per 1,000 women in a specific age group for a specified geographic area and for a specific point in time, usually a calendar year. For example, all the births to women age 20 to 24 in the United States in 2015.
• Completed fertility rate (CFR): This metric is the number of children actually born per woman in a cohort of women (typically those born in a country around the same time) up to the end of their childbearing years.

These distinctions are why reporting on fertility rates often give different dates for significant events, such as “record lows.” Recent news headlines reporting that “fertility rates in 2020 dropped to another record low” are referring to the GFR and TFR, both of which hit a record low last year. The CFR reached its record low in 2006. Because some women are having children after age 44, the general fertility rate might be at a record low and yet the total number of mothers might still be relatively high.  

What is the replacement rate?

The replacement rate is the total fertility rate necessary to replace both the mother and the father, and accounts for the number of children who won’t live to childbearing age.

There are several factors—such as migration, war, and disease—that can affect how many people in a country needed to be replaced each year. But assuming such factors aren’t having a major and unexpected impact on population, the total fertility rate that equals the replacement rate is 2.1 children per woman. This is the number of children generally needed per woman to ensure a broadly stable population, though it can vary slightly in countries where children are more likely to live to adulthood. In the United States the replacement rate is closer to 2.08. 

If the replacement rate is 2.1 over an extended period of time, the population in a country will remain about the same. If it increases or decreases, the population of the next generation will also increase or decrease. 

Why does it matter if the fertility rate declines?

In a population where the replacement rate is around 2.1, the number of people moving through each cycle of human development (e.g, childhood, adolescence, early adulthood, midline, late adulthood) is roughly the same at each stage. But if a generation is larger or smaller than other generations, it can have an effect on society that lasts numerous decades. For example, if there is a “baby boom”—an unexpected increase in the number of children born in a generation—a nation may need to build more schools, from the elementary to the collegiate level. But the next generation, if it is not equal in size, will be left with educational infrastructure that is not needed. 

In most developed countries, such as the U.S., the social safety net is structured in a way that makes young people a form of “old-age insurance.” Societies create a pay-as-you-go system that is dependent on there being a greater number of younger people of working age relative to those of retirement age. For instance, Social Security uses the payroll taxes of current workers to directly pay the monthly benefits of older, retired workers. This pay-as-you-go approach works best when there is a high ratio of workers to beneficiaries, such as in 1945, when there were 41.9 workers for every retiree receiving Social Security. But the system becomes more difficult to maintain when the ratio is reversed. In 2018 the ratio was 2.8 workers for every retiree, and it’s expected to drop to 2.2 by 2049. Because of a falling fertility rate, that number could drop close to 1:1 by the time younger millennials and Gen-Z reaches retirement age. 

Long-term declines in fertility can also have effects that ripple throughout society. For instance, as more resources are needed for the elderly relative to the young, they could be viewed as a “burden on society.” This could lead, as it has in Europe, to an acceptance of voluntary euthanasia. Population declines also cause hardship for rural areas. Because fewer children are born, fewer stay in the area to take care of the elderly population. This can require significant shifts in numerous areas, ranging from public health to church planting.