Sexual abstinence may be used as a form of birth control, meaning either not engaging in any type of sexual activity, or specifically not engaging in vaginal intercourse, while engaging in other forms of non-vaginal sex.[88][89] Complete sexual abstinence is 100% effective in preventing pregnancy.[90][91] However, among those who take a pledge to abstain from premarital sex, as many as 88% who engage in sex, do so prior to marriage.[92] The choice to abstain from sex cannot protect against pregnancy as a result of rape, and public health efforts emphasizing abstinence to reduce unwanted pregnancy may have limited effectiveness, especially in developing countries and among disadvantaged groups.[93][94]