(AP) -- The U.S. teen birth rate hit an all-time low in 2009 - a decline that stunned experts say is partly because of the economy.
The birth rate for teenagers fell to 39 births per 1,000 girls, ages 15 through 19, according to a government report released Tuesday. It was a 6 percent decline from the previous year, and the lowest rate since health officials started tracking that data in 1940.
Experts say the recent recession - from December 2007 to June 2009 - was a major factor driving down births overall, and experts say there's good reason to think it affect would-be teen mothers.
"I'm not suggesting that teens are examining futures of 401ks or how the market is doing," said Sarah Brown, chief executive of the National Campaign to Prevent Teen and Unplanned Pregnancy.
"But I think they are living in families that experience that stress. They are living next door to families that lost their jobs... The recession has touched us all," said Brown.
Teenage moms, who account for about 10 percent of the nation's births, are not unique. The total number of births also has been dropping, as have birth rates among all women except those 40 and older.
For comparison look to the peak year of teen births - 1957. There were about 96 births per 1,000 teen girls that year, but it was a different era, when women married younger, said Stephanie Ventura, a co-author of the report issued by the federal Centers for Disease Control and Prevention. The CDC births report is based on a review of most birth certificates for 2009.
Overall, about 4.1 million babies were born in 2009, down almost 3 percent from 2008. It's the second consecutive annual decline in births, after births had been increasing since 2000.
The trend may continue: A preliminary count of U.S. births through the first six months of this year suggests a continuing drop, CDC officials said.
A decline in immigration to the United States is another factor experts cite for the lower birth rate.
Other findings in the new report include:
-The cesarean delivery rate rose yet again, to about 33 percent of births. The C-section rate has been rising every year since 1996.
-The pre-term birth rate, for infants delivered at less than 37 weeks of pregnancy, dropped for the third straight year to about 12 percent of all births. It had been generally increasing since the early 1980s.
-Birth rates were down from 2008 in almost every age group of women of childbearing. The birth rate for women in their early 20's plummeted 7 percent, the largest decline for that age group since 1973.
The one exception was women older then 40 - a group that may be more concerned with declining fertility than the economy. The birth rate for women ages 40-44 was up 3 percent from 2008, to about 10 births per 1,000 women. That's the highest rate for that group since 1967.
CDC officials said the most striking change was in the decline among teens.
Some believe popular culture also has played an important role. The issue of teen pregnancy got a lot of attention through Bristol Palin, the unmarried pregnant daughter of former GOP vice presidential candidate Sarah Palin. Bristol Palin had a baby boy in December 2008. Teen pregnancy is also cast in a harsh light by "Sixteen and Pregnant," a popular MTV reality show which first aired in 2009 and chronicles the difficulties teen moms face.
Also, health officials and advocates may they deserve some credit. For decades, they and others have been emphasizing the hazards of teen pregnancy, including higher high school dropout rates among the mothers and higher odds for health and other problems for their children. The cumulative effect of public health campaigns may have played an important role in pushing down the teen birth rate, Ventura said.
But experts acknowledge they are speculating. And none was able to explain an uptick in the teen birth rate in 2006 and 2007.
Also, there's reason to rein in celebration of the 2009 numbers. The U.S. teen birth rate continues to be far higher than that of 16 other developed countries, according to a 2007 United Nations comparison that Brown cited.
Still, news of the large decline was a stunning and exciting surprise for advocates, Brown noted. "This is like a Christmas present," she said.
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More information: The CDC report: http://www.cdc.gov/nchs