American women are having fewer babies than ever, according to recent CDC data.

Expand chart Data: CDC; Chart: Axios Visuals

Between the lines: Even with low fertility rates, the overall population — along with GDP — will continue to grow until at least 2050, according to the Census projections. But this growth will increasingly rely on immigration.

Immigration already accounted for almost half of population growth in the U.S. last year, and it is expected to become the biggest driver of population growth in 2030, according to the Census Bureau.

Fertility rates tend to fall in response to a bad economy.

In the 1970s — as baby boomers entered the workforce, the pill and IUDs became more common, abortion was legalized, the oil shock hit and the economy struggled — the total fertility rate plummeted to levels near what we have today.

— as baby boomers entered the workforce, the pill and IUDs became more common, abortion was legalized, the oil shock hit and the economy struggled — the total fertility rate plummeted to levels near what we have today. But it the late 1980s and onward during economic growth, it climbed to stay near replacement levels (2.1 births per woman), making the U.S. somewhat of an anomaly among developed economies, according to Global Aging Institute president Richard Jackson.

But during the current economic boom, fertility rates have been falling.

High costs of education, stagnant wages and more women working and delaying childbirth have all contributed, Richard Cincotta, director of the Global Political Demography Program at the Stimson Center, told Axios.

Whether fertility rates recover with the economy often depends on people's long-term expectations about future living standards, according to Jackson. "That's been seriously eroded since the Great Recession among millennials," he said. "They're not responding to the near-term economy because confidence in the long-term economy has been seriously dented."

What to watch: If fertility rates remain low or fall further, there could be fewer people entering the workforce in the future and GDP growth could slow, demographers say. Maintaining high levels of immigration could become even more important.

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