The U.S. birthrate in 2011 hit a historic low because of the economic crisis, which reduced reproduction among the immigrant population by 14 percent between 2007 and 2010.

"The recession is the only explanation for this change," D'Vera Cohn, author of the Pew Research Center report on the drop in fertility in the world's leading economy, told Efe.

The U.S. birthrate is at its lowest since records started being kept in 1920.

In 2011 it stood at 63.2 births for every 1,000 women, half the rate during the post-World War II baby boom, a period of growing prosperity for all social classes.

The biggest regression is seen among women of the immigrant community, one of the groups hit hardest by economic woes.

"Both our research and relevant data from other sources show that fertility tends to drop during a recession, and it is the groups most affected economically that are most discouraged about having children," Cohn said.

The drop in birthrate among the immigrant population between 2007 and 2010 is greater than the general average: 14 percent.

And it dropped 23 percent among Mexicans, who represent 63 percent of the total of the U.S. Hispanic population.

Over the past two decades, the Hispanic population grew considerably, but it has now gone from a birthrate of 136.9 for every 1,000 women to 96.3 at present, the biggest drop of any population segment.

Nonetheless, immigrants remain the most fertile population group.

In May, for the first time in United States history, the majority of the population younger than 1 year old lived in minority families, the Census Bureau said.

The Pew Research Center study also showed that teen pregnancy is more common among the U.S.-born population than among immigrants. EFE