Science has finally proved that if you don't use condoms or birth control you can, in fact, get pregnant.

Dr. Annie Dude, a resident in obstetrics and gynecology at Duke University Medical Center, compiled surveys of more than 2,000 women between the ages of 15 and 24 and found that 31 percent of them had used the "pull-out method," also known as coitus interruptus.

The study found that 21 percent of those women had an unintended pregnancy, compared to 13 percent of women who used other forms of birth control.

Of course, the fact that women can get pregnant from unprotected sex isn't exactly a revelation. But the fact that nearly one in three women use the withdrawal method is significant. It could point to a lack of education from the medical community, as Dude explained to U.S. News & World Report, saying, "My overall take is that doctors think this is such an antiquated method of birth control that they don't really think to address it with their patients."

Why is the pull-out method so ineffective? While that might sound obvious, a previous study has shown that when done right, it is "only slightly less effective than the male condom at preventing pregnancy."

The problem, as Slate's Amanda Marcotte pointed out, is that the people who use it might not be very rigorous about preventing pregnancy in the first place:

It might also be that use of withdrawal suggests an overall pattern of inconsistent contraception use. Unfortunately, the patchwork approach — going on and off the pill, trying to remember to have condoms on hand but often forgetting, refusing to have condoms on hand unless you're sure it's going to happen, and, if all else fails, hoping he pulls out on time — is all too common, as this study suggests. [Slate]

Ultimately, studying how young couples do or do not use birth control is important because three-quarters of births to women ages 15 to 20 are unintended.

"The main point this study makes is that withdrawal as a form of contraception is more common than we thought," Dr. Nancy Stanwood, section chief of family planning at the Yale University School of Medicine, told Reuters. "Women who use it might not recognize the degree of the risks they're taking."