Over the last decade and a half, fertility rates in the U.S. have declined from above‐​replacement at the top of the Great Recession, to below replacement rate a few years later. Since then, fertility rates have continued along a downward trajectory.

More recently, the total fertility rate—a measure of the expected number of children a woman will have if she survives her reproductive years, and a sum of age‐​specific fertility rates—declined to record lows (1.64) during the pandemic. In 2021, U.S. births ticked up enough to put birth rates inline with their pre‐​pandemic, downward trend and remain at sub‐​replacement levels.

For a variety of reasons, sub‐​replacement level fertility and continued fertility decline have caused concern among researchers and commentators alike. For one thing, assuming that sub‐​replacement level fertility is sustained, and that it is not mitigated or offset by population momentum, increasing life expectancy, or immigration, population size will decline over time.^[1] This could have economic and fiscal implications, including declining overall GDP or widening solvency issues for major federal programs and public pensions.

Although most commentators focus on recent fertility decline, the history of declining fertility begins much earlier. During the hundred year period from 1800 to 1900, total fertility rates fell from seven children per woman to less than four (Figure 1) and continued to fall. This occurred during a period of rapid economic and social change that included industrialization, urbanization, changes in medicine and mortality, and implementation of compulsory childhood education in most states.

Then, in the first third of the twentieth century, fertility continued to decline, until the total fertility rate fell below the replacement rate prior to the second World War. Americans worried about low fertility in the pre‐​war years, during the war, and afterwards, though by the end of World War II fertility had begun to rebound. This “baby boom” shocked demographers of the day, who did not forecast it (in fact, quite the opposite, demographers projected a continued downward trend for fertility).

Later, demographers were unable to predict the end of the baby boom. Today, the cause of the baby boom is still debated, with various researchers arguing that factors including technological improvements, women’s labor market opportunities, and wartime mobilization motivated it. Adding to the mystery, the baby boom occurred both in countries that were involved in the war and countries that weren’t.

In addition to experiencing sub‐​replacement fertility briefly in the late ‘30s and early ‘40s, the U.S. also experienced sub‐​replacement fertility during the three‐​decade‐​plus period from 1972 through 2005 (admittedly, during the latter half of this period, the fertility rate was relatively stable and remained close to replacement level).

Although many seem to think of falling fertility as self‐​evidently negative, some historical context helps to temper this impulse. For instance, during the longest sustained decline in fertility (1800–1940), child mortality dropped by around 86 percent. This arguably motivated at least a portion of the decline in fertility, since under diminishing child mortality, couples did not need to have as many births in order to achieve the same family size.

Similarly, during certain periods of (post‐​1930s) fertility decline, female labor force participation increased inversely with fertility.^[2] So, as women gained economic and social freedoms and joined the workforce, they also had fewer children. Though there is some debate whether increased labor force participation was a cause or a consequence of fertility decline during this period, women obtaining economic and social freedoms should be celebrated.

Likewise, certain causes of the most recent (2007–2022) fertility decline are not self‐​evidently negative: a significant portion of the recent decline in fertility is a result of a decline in teen births, which peaked in the ‘90s and fell 75 percent from 1991 until 2020. Teen fertility decline accelerated since 2007, just as U.S. fertility began its most recent decline.

Most people would consider the decline in teen births a positive development, as teenagers do not typically have the financial independence, academic or professional training, emotional development, and/​or a supportive and committed partner that makes caring for an infant easier or even possible. Indeed, in the 90s, the high rate of teen births was a major focus of policy scholarship.

In line with the idea that a significant piece of the recent decline in fertility is due to a decline in teenage births, another paper finds that 35 percent of the decline in fertility in the years between 2007 and 2016 is due to a reduction in unintended births, or births that were either undesired or occurred earlier than the mother would like. If true, a substantial portion of the decline in fertility is a function of women meeting their fertility preferences, not missing them.

Although fertility decline may have economic, fiscal, or social consequences, it is critical that information consumers and policymakers understand that fertility does not always decline for nefarious reasons. The history of U.S. fertility helps to provide some clarity on this account.