By MIKE STOBBE The Associated Press updated 1 hour 26 minutes ago 2010-12-21T18:39:49 — 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, blamed on the weak job market, is another factor cited for the lower birth rate. A large proportion of immigrants are Hispanic, and Hispanics accounted for nearly 1 in 4 births in 2009. The birth rate among Hispanic teens is the highest of any ethnic group with 70 births per 1,000 girls in 2009. However, that rate, too, was down from the previous year.