“The number of births in the U.S. today is simply not enough by itself to keep the population stable,” Mosher said. Noting the fertility declines over the past three years were mostly among women under 30, Kasey Buckles, an economics professor at Notre Dame, said the data indicated the decrease most likely came from a drop in unwanted pregnancies and people just being more “intentional about their fertility.”

The United States birth rate dropped again last year, hitting a 30-year low and raising concerns about the future of American society and economic growth.

The number of U.S. babies born last year fell 2 percent from 2016, from 3.95 million to 3.85 million, according to data released last week by the Centers for Disease Control and Prevention’s National Center for Health Statistics.

The fertility rate—the number of births per 1,000 women of reproductive age—also hit a record low, down 3 percent since 2016 to 60.2 births per 1,000 women ages 15 to 44. The total fertility rate—the theoretical total number of births each woman would have in a lifetime if she followed the current fertility rate—also dropped 3 percent, to 1.765 births per woman.

The United States has been below replacement fertility (2,100 births per 1,000 women) for the greater part of the last 45 years. Robust immigration has staved off some of the negative effects of population decline, but not all.

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