the penetrative role during anal sex because of its association with dominance, because it is made more alluring by a female partner or society in general insisting that it is forbidden, or because it presents an additional option for penetration. While some women find being a receptive partner during anal intercourse painful or uncomfortable, or only engage in the act to please a male sexual partner, other women find the activity pleasurable or prefer it to vaginal intercourse. In a 2010 clinical review article of heterosexual anal sex, anal intercourse is used to specifically denote penile-anal penetration, and anal sex is used to denote any form of anal sexual activity. The review suggests that anal sex is exotic among the sexual practices of some heterosexuals and that "for a certain number of heterosexuals, anal intercourse is pleasurable, exciting, and perhaps considered more intimate than vaginal sex". Anal intercourse is sometimes used as a substitute for vaginal intercourse during menstruation. The likelihood of pregnancy occurring during anal sex is greatly reduced, as anal sex alone cannot lead to pregnancy unless sperm is somehow transported to the vaginal opening. Because of this, some couples practice anal intercourse as a form of contraception, often in the absence of a condom. Male-to-female anal sex is commonly viewed as a way of preserving female virginity because it is non-procreative and does not tear the hymen; a person, especially a teenage girl or woman, who engages in anal sex or other sexual activity with no history of having engaged in vaginal intercourse is often regarded among heterosexuals and researchers as not having yet experienced virginity loss. This is sometimes called technical virginity. Heterosexuals may view anal sex as "fooling around" or as foreplay; scholar Laura M. Carpenter stated that this view "dates to the late 1600s, with explicit 'rules' appearing around the turn of the twentieth century, as in marriage manuals defining petting as 'literally every caress known to married couples but does not include complete sexual intercourse.'" Prevalence Because most research on anal intercourse addresses men who have sex with men, little data exists on the prevalence of anal intercourse among heterosexual couples. In Kimberly R. McBride's 2010 clinical review on heterosexual anal intercourse and other forms of anal sexual activity, it is suggested that changing norms may affect the frequency of heterosexual anal sex. McBride and her colleagues investigated the prevalence of non-intercourse anal