By Veronica Hackethal, MD

NEW YORK (Reuters Health) - Many young women use the "pull-out method" for birth control, and they tend to have more unintended pregnancies than other women, a new study suggests.

Researchers compiling surveys from more than 2,000 women ages 15 to 24 found 31 percent had used the pull-out method, also known as withdrawal or coitus interruptus, over the last two years.

Of those women, 21 percent reported having an unintended pregnancy. In contrast, 13 percent of women who only used other forms of birth control got pregnant unintentionally.

"We found that people tend to use the withdrawal method when they're not really planning ahead," Dr. Annie Dude, a resident in obstetrics and gynecology at the Duke University Medical Center in Durham, North Carolina, and lead author of the paper, said.

"It's a lot more common than many people realize," she told Reuters Health.

And, Dude added, her study shows withdrawal doesn't work as well as other birth control methods for avoiding unintended pregnancies.

The most effective birth control methods are longer-term reversible contraceptives, such as intrauterine devices (IUDs) and implants that go under the skin. Less than one woman in 100 will get pregnant each year using these forms of birth control.

Slightly less effective forms include the Depo-Provera hormone shot, the Pill, the ring and the patch, all with failure rates between two and nine percent per year.

When used properly, withdrawal carries about the same risk of pregnancy as condoms and diaphragms, with failure rates of 15 to 24 percent per year. But because withdrawal requires good timing and communication between partners, some experts estimate that failure rates may be even higher, between 18 and 28 percent.

SOURCE: http://bit.ly/16oIc70 Obstetrics and Gynecology, online August 5, 2013.