"Teens tend to emulate young adults," Santelli said. "They are less influenced directly by the economy than by people."
Studies show that since 2007, larger percentages of sexually active teenage girls are using the pill and other effective birth control. Studies also show a small decline in the proportion of girls ages 15 through 17 who say they've had sex, Santelli noted.
The new birth report also noted a fourth straight decline in a calculation of how many children women have over their lifetimes, based on the birth rates of a given year.
A rate of a little more than 2 children per woman means each couple is helping keep the population stable. The U.S. rate last year was slightly below 1.9.
Countries with rates close to 1 — such as Japan and Italy — face future labor shortages and eroding tax bases as they fail to reproduce enough to take care of their aging elders.
Officials here aren't as worried.
The U.S. replacement rate is still close to 2. And it has dropped in the past and then bounced back up again, said Ventura, an official at the CDC's National Center for Health Statistics.
"And we haven't seen any studies that show couples want to have fewer children or no children," she added.
One more report highlight: The U.S. C-section rate may have finally peaked at just under 33 percent, the same level as last year.
Cesarean deliveries are sometimes medically necessary. But health officials have worried that many C-sections are done out of convenience or unwarranted caution, and in the 1980s set a goal of keeping the national rate at 15 percent.
The C-section rate had been rising steadily since 1996, until it dropped slightly in 2010.
"It does suggest the upward trend may be halted," said Joyce Martin, a CDC epidemiologist who co-authored the new report. But CDC officials want a few more years of data before declaring victory, she added.
CDC report: http://www.cdc.gov/nchs/
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