Conventional analyses of the obstacles to contraceptive use in Africa focus on the social value attributed to high fertility, the fear of side effects and problems of accessing contraception. This article studies the range of situations that can lead to unplanned pregnancy and aims to identify the social rationales that foster such situations. Two hundred semi-structured interviews were conducted in 2006-2007 in the capitals of Burkina Faso, Ghana, Morocco and Senegal as part of the survey on Emergency Contraception in Africa (ECAF). The analyses reveal that simultaneously trying to observe reproductive and sexual norms – in which a double standard prohibits premarital sex for young women while endorsing the primacy of male sexual pleasure – leads to unprotected or poorly protected intercourse. While the factors are relatively similar in the four countries, the rigidity of the norms in question differs from one to another, notably with regard to premarital sexuality. Finally, the question of effective contraceptive use goes far beyond the issue of «unmet needs», a central concept in the literature which focuses on non-use of contraception.