The number of US babies born to teen mothers dropped to record lows in 2011, according to data from the Centers for Disease Control and Prevention.

Fewer women gave birth in their 20s as well than in prior years, the researchers said in findings published in Pediatrics - but the birth rate increased for those in their late 30s and early 40s.

"The economy has declined, and that certainly is a factor that goes into people's decisions about having a child," said CDC statistician Brady Hamilton, lead author of the report.

"Women may say to themselves, 'It's not a particularly good time right now... let's wait a little bit.'"

Older women, however, are typically more secure in their employment, and understand that they don't have as long to wait if they want to get pregnant, he said.

The new data showed an eight percent drop in teen births between 2010 and 2011, with just over three percent of 15- to 19-year-olds having babies during that period.

Hamilton and his colleagues calculated that 3.6 million more babies would have been born to women in that age group over the last two decades had the teen birth rate not been falling since a peak in 1991.

On the other end of the spectrum, the birth rate among 35- to 39-year-olds increased by three percent over 2010 figures. In 2011, 4.7 percent of women in their late 30s and just over one percent in their early 40s had a baby.

Other results from the report showed a continued decline in babies born prematurely or small, and an unchanged rate of infant deaths.

Black and Hispanic mothers continued to be more likely to have a premature baby than white women, but rates declined among all races. Infant mortality was more than twice as high among babies born to black mothers as in babies of white mothers, death records showed.

Hamilton said the decline in teen births, in particular, is especially welcome news and reflects the efforts of programs and policies targeting that age group.

"It's definitely consistent with the trends that we've seen, and it's obviously good news overall," said Krishna Upadhya, who studies teen pregnancy at the Johns Hopkins School of Medicine.

"I think the main thing behind this is increased contraceptive use, and better contraceptive use," added Upadhya, who wasn't involved in the new research.

However, she added that there are still some parts of the country where both condoms and long-acting forms of contraception, such as intrauterine devices (IUDs) are harder for teens to access.