THUS, OPEN BORDERS:

The United States has a higher fertility rate than many other developed countries, bolstered by Hispanic immigrants, who are more likely than whites to be in their childbearing years. When rates are lower, as they are in countries like Germany and Japan, youth populations shrink, which can lead over time to a reduction in the size of the labor force and diminished tax bases.

"There's a widespread perception that a moderately growing population is advantageous for economic growth and for a growing society," said Hans-Peter Kohler, a professor of sociology at the University of Pennsylvania.

That is why news of the 2012 figures had demographers buzzing.

"It's exciting," Professor Kohler said. "My prediction would be that we'll see further stabilization and possibly growth in 2013."

Follow @brothersjudd