Gretchen Livingston, a senior researcher at the Pew Hispanic Center and the Pew Social & Demographic Trends Project, said the total number of births in 2011 -- 3,953,590 -- represented a 1 percent decline since 2010.
Livingston, who used government data for the analysis, said from 2010-11, birth rates among teens ages 15-19 dropped 8 percent, and among women ages 20-24 declined 5 percent -- in both cases reaching historic lows in 2011.
However, the birth rate for women ages 40-44 rose 1 percent, to 10.3 births per 1,000 women in that age group. The last time the rate came that close was in 1967, when it was 10.6, Livingston said.
Birth rates among women in their late 20s declined 1 percent, to the lowest point in 2011 since 1976, while among women in their early 30s, birth rates held stable. Birth rates for women in their late 30s rose for the first time since the onset of the recession, Livingston said.
The U.S. birth rate, which had been relatively stable, declined 9 percent from 2007-11, but the pace of decline has slowed. From 2009-10, the overall U.S. birth rate declined by 3.2 percent and from 2010-11 the decline was smaller still at 1.4 percent.