The U.S. abortion rate in 2009 fell to its lowest level in a decade -- 15.1 abortions per 1,000 women ages 15–44 -- with the U.S. Centers for Disease Control and Prevention, or CDC, crediting the development to one not-so-surprising factor: effective contraception.

Abortions dipped by 5 percent between 2008 and 2009, the most recent years for which data is available, representing the largest single-year drop in the decade from 2000 to 2009. The data indicate women may have turned to more dependable birth-control methods during the Great Recession, leading some experts to conclude that when times get economically tough, women want to have fewer children.

"They stick to straight and narrow ... and they are more careful about birth control," Elizabeth Ananat, a Duke University assistant professor of public policy and economics who has researched abortions, told the Associated Press.

In April, the CDC similarly reported the nation’s teen-pregnancy rate fell 9 percent between 2009 and 2010. The agency also credited that decline to the widespread use of birth control, which it noted is more prevalent in states that require comprehensive sex education in schools.

States encouraging abstinence-only sex education -- such as Alabama, Arkansas, Mississippi, and Texas -- had the highest teen-pregnancy rates.

Nearly all states report abortion figures to the CDC, but it is done on a voluntary basis. One notable exception is California, which has both the largest population and the largest number of abortion providers.

Although the CDC has estimated there are about 1 million abortions in the U.S. annually, the agency noted there were 784,507 abortions in the 48 of 52 reporting areas that provided figures for 2009. In the CDC's latest trend analysis, it used abortion data from 45 reporting areas -- 43 states and two cities (New York and Washington) -- that consistently reported the relevant figures for the 10 years from 2000 to 2009.