One foreseen factor behind the dropoff in childbearing is the rapid decline in Hispanic-American fertility.

For several decades, high Hispanic childbearing has been driving U.S. population growth. White fertility has been under the 2.1 replacement rate for decades, and ranged from 1.7 to 1.9 in the 2000s. The TFR for black Americans first fell below 2.1 in the early 2000s.

But the number of children per Hispanic-American woman has plummeted from just under three in 1990 and 2.7 as recently as 2008 to 2.19 in 2012, just above the replacement rate.

That decline has been mirrored in other Hispanic countries. Mexico’s TFR has fallen precipitously, from 6.7 in 1970 to 2.2 in 2012, according to the World Bank. A similar decline has taken place in El Salvador, and to a lesser extent Honduras and Guatemala, all three prominent countries of origin for American Hispanics.