Americans Are Having Fewer Babies. What Does That Mean for the Country? - WSJ

“There is the birthrate and there is the number of children people have in their lifetime, and they are not the same,” she says. The total fertility rate of 1.57 is a snapshot statistic, not a portrait of any particular woman’s life, she says. It estimates the average number of children a woman would have if she lived through her childbearing years experiencing current rates.

That may not be a good measure of what American women are actually doing. “If you look at women in their 50s who have completed childbearing—what’s called the ‘completed cohort fertility rate’—that number has been hovering right around 1.9 to 2,” Bailey says.

Some of the explanation can be found in another number buried in the data: More than one-quarter of the decline in the fertility rate is accounted for by falling rates of teen pregnancy since 2007, according to recent analysis by Alison Gemmill, associate professor of epidemiology at UCLA, and Magali Barbieri, a researcher in the department of demography at the University of California at Berkeley.