Numbers released Wednesday show 2011 had the lowest birth rate in United States history.

Numbers released Wednesday show 2011 brought the lowest birth rate in American history. And experts are beginning to question the theory that it's a lingering effect of the recession.

Births peaked in 2007 at 4.3 million, according to the National Vital Statistics Report, but have been dropping every since. And a predicted post-recession "mini baby boom" has never materialized.

"Substantial declines in just one year among certain segments of women suggest a deeper and potentially longer-lasting change in childbearing," wrote Sharon Jayson of USA Today. Demographers have told her that fertility rates usually rise a year or two after a recession ends. This one didn't.

According to the National Center for Health Statistics, in 2011:

Births to teens dropped 10 percent, the lowest number since 1946. Teen birth rates fell to 31.3 per 1,000, the lowest since 1940.

Births to women 20-24 fell 3 percent from 2010 to 2011 and the birth rate dropped 5 percent. At 85.3 births per 1,000, the birth rate has never been lower in United States history.

The birth rate for those ages 25-29, at 107.2 per 1,000, is the lowest since 1976.

The birth rate is also down for unmarried women.

"It is hard to tell whether this is movement towards a long-term trend of lower fertility or the tail end of the fertility effect of a major recession," Steve Martin, assistant professor of sociology at Christopher Newport University in Newport News, Va., told Jayson. "Reading all those trends together, it could indicate the United States is continuing to move towards a later birth pattern." Jayson noted that's already happening in other developed countries.

Ken Johnson, a demographer at the University of New Hampshire's Carsey Institute, told the Wall Street Journal that the decreased fertility echoes what happened in the Great Depression. "The young women never made up for the births that they didn't have."

The most startling birth rate drop he noted was among young Hispanic women ages 20-25. Their fertility rate dropped from 165 to 115 per 1,000 in 2007. Fertility for women of all races age 35-39 has stayed relatively flat.

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