Some experts theorize that some women believed they couldn't afford to get pregnant.
"They stick to straight and narrow," said Elizabeth Ananat, a Duke University researcher, "and they are more careful about birth control."
Abortions have been dropping slightly over the last decade. But before this latest report, they seemed to have pretty much leveled off.
Because not all states report abortion numbers to the federal government, the CDC used numbers from the 43 states and two cities that have been sending data consistently for at least 10 years to calculate year-to-year comparisons.
Researchers found that abortions per 1,000 women of childbearing age fell from 15.9 in 2008 to 15.1 in 2009. That translates to nearly 38,000 fewer abortions.
By all accounts, contraception is playing a role in lowering the numbers.
Some experts cite a government study released earlier this year suggesting that about 60 percent of teenage girls who have sex use the most effective kinds of contraception, including the pill and patch. That's up from the mid-1990s, when fewer than half used the best kinds.
Experts also pointed to the growing use of IUDs, or intrauterine devices, the T-shaped plastic sperm-killers that a doctor inserts into the uterus. IUDs essentially prevent "user error," said Rachel Jones, a Guttmacher Institute researcher.
Another factor may be the growing use of the morning-after pill, a form of emergency contraception that has been increasingly easier to get.
Underlying all this may be the economy, which was in recession from December 2007 until June 2009. Even well afterward, polls showed most Americans remained worried about the economy.
You might think a downturn would lead to more abortions by women who are struggling. But John Santelli, a Columbia University researcher, said: "The economy seems to be having a fundamental effect on pregnancies, not abortions."