The U.S. birthrate languishes at its lowest level in history. So when our friend and colleague Herman Wong suggested running the numbers on only children, we lit up with the cheap joy of answering a question to which we already knew the answer. With fewer kids overall, Americans are surely cranking out one-hit wonders in record numbers, right?

Not so fast!

Every two years, the Census Bureau quietly appends a battery of fertility-related questions to its workhorse monthly questionnaire, the Current Population Survey, our go-to source for everything from the unemployment rate to Americans' moving habits. It's smaller than the immense annual American Community Survey, but it's one of the few major surveys that asks how many times American women have given birth.

As we analyzed the latest figures, from 2022, our brains spun in our skulls: Since the mid-1980s, the rate at which we produce only children has remained absolutely flat. Something like 1 in 5 American women ages 25 to 44 are one and done.

That's bizarre, given birthrates! But let's zoom out and look at the whole universe of possible family sizes.

First, we noted that families with three or more kids plunged in the 1980s, as birth control, education and greater opportunity helped women pile into the workforce. That's also when only children rose to their current level. Families shifted again after the Great Recession when, among women 25 to 44, even having two children lost its luster. The number of women who had zero children soared. Only children held steady.