Sex is fun. And after the 1970s sexual revolution and the introduction of birth control pills, sex became far more recreational than it was in previous generations, as the risk of pregnancy was reduced to almost nothing. But for a variety of reasons, some young women opt out of birth control pills — whether due to fear of the pill's negative effects on the body or money issues or religious stigmas.

Increasingly, women are reverting to a practice not widely seen since before the introduction of birth control pills: the withdrawal method. The idea is simple — when engaging in sex, the man withdraws before he begins to orgasm, in an attempt to avoid unwanted pregnancy. But a new study published in the journal Obstetrics & Gynecology proves that this old-fashioned method is unreliable and gives both parties a false sense of security.

Read more: US Teen Birth Rates at Lowest Level Since 1976

The Risk

"Our study showed that use of withdrawal for contraception is very common, but it doesn't work as well as other methods," said Dr. Annie Dude, study author and resident in the Department of Obstetrics and Gynecology at Duke University Medical Center.

The study looked at surveys taken by women between the ages of 15 and 24 from 2002 to 2008. By analyzing the answers from 2,200 women, researchers determined that 31 percent of women in this age group use the pull-out method as a means of birth control. Of those who used it, 21 percent became pregnant — far exceeding the less than one percent chance of pregnancy with birth control pills. This finding was also compared to the 13 percent of pregnancies from all other forms of birth control asked about in the study, such as condoms and intrauterine device (IUD) implants, which do have a risk of failure if used improperly.

Additionally, those who used the withdrawal method were 7.5 percent more likely to use emergency contraception. This includes the usage of Plan B or Next Choice.

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Effective Methods

Dude suggests that doctors recommend IUD to their patients or implants in the arm, both of which prevent pregnancy in the long term.

"There are certainly issues of access for the age group in this study — young women ages 15 to 24," said Dr. Kari Braaten, an obstetrician-gynecologist at Brigham and Women's Hospital in Boston. "I'd like to stress that one of the things we need to do is improve access to long-acting methods like IUDs and implants, so we minimize these experiences and encounters where women find themselves needing to rely on an 'emergency' form of contraception like withdrawal or Plan B when they're otherwise unprepared."

Source: Dude A, Neustadt A, Martins S, Gilliam M. Use of Withdrawal and Unintended Pregnancy Among Females 15-24 Years of Age. Obstetrics & Gynecology. 2013.