ATLANTA — 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 today. 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 affects 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.