Women in the U.S. are increasingly using long-acting methods of birth control, such as intrauterine devices (IUDs), while the use of short-term contraception, such as birth control pills, as well as sterilization procedures have slightly decreased, according to a new study.

The percentage of U.S. women using birth control who reported using a long-acting method rose from 2.4 percent in 2002 to 3.7 percent in 2007 and to 8.5 percent in 2009. Over this same time, the percentages of women who reported using either permanent or short-term methods of birth control decreased.

"The average age at first sex is around 17, and the average age at first birth close to 25. As a result, the period during which women are at risk for unplanned pregnancy is much longer than it used to be," said study author Dr. Lawrence Finer, of the Guttmacher Institute.

This means that protecting against pregnancy for a longer time, without requiring a woman's frequent attention, could greatly benefit women — especially young women, who have the highest rates of unintended pregnancy, Finer said.

The researchers used data gathered during the National Survey of Family Growth, which includes U.S. women ages 15 to 44. Women completed the surveys in their homes, and all information was self-reported. The researchers surveyed 4,600 women in 2002, 3,400 in 2007 and 3,900 women in 2009.

Women between ages 25 and 39 and women who already had one or more children were more likely to use long-acting contraception, the results showed. This supports the idea that most people consider long-acting contraception to be a method that should be used after child-bearing.

Long-acting contraception also has higher up-front costs than other methods, which may deter younger women, according to the researchers. IUDs can cost up to $500, according to Planned Parenthood.

However, although women younger than 25 were less likely to use long-acting methods than other groups, there was still an increase in use among women of this age, from 1 percent of all women ages 15 to 19 in 2007, to 4 percent in 2009.

Despite the rise in use of long-acting methods, the most common form of birth control used by women over age 35 was sterilization, and among women under age 35, other methods such as the pill remained more common.

The study was published Monday (July 16) in Fertility and Sterility.

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