Every year in the United States, nearly half of all pregnancies (approximately 3.5 million) are unintended. Approximately half of these pregnancies result from contraceptive failure or inadequate contraceptive technique. Others occur owing to a failure to use any type of contraception, because of unanticipated and thus unprotected sexual activity, and as a result of sexual assault or coercion. Although not all unintended pregnancies are unwanted, emergency contraception is generally used when pregnancy is not desired. Given the large number of unintended pregnancies in the United States and elsewhere, emergency contraception remains a highly underused method of contraception.<sup>5 Chiou V.M., Shrier L.Y., Emans S.J. Emergency postcoital contraception J Pediatr Adolesc Gynecol 1998 ;  11 : 61-72

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For at least 2 decades, safe and effective emergency contraception has been available in the United States; however, many practitioners and patients have inadequate information about its use. Studies have shown that as many as 25% to 30% of women have never even heard of emergency contraception, 10% know how to get it, but only 3% have ever used it.<sup>29 Trussell J., Ellertson C. Efficacy of emergency contraception Fertility Control Reviews 1995 ;  4 : 8-11

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The American College of Obstetricians and Gynecologists has defined emergency contraception as “a therapy for women who experience an act of unprotected sexual intercourse.”<sup>1 American College of Obstetricians and Gynecologists   Emergency oral contraception. Practice Patterns No. 3 Washington, DC: ACOG (1996). 

Haga clic aquí para ir a la sección de Referencias</sup> It has been also described as postcoital contraception and “the morning after pill.” The procedure is most appropriately described as emergency contraception because there are methods besides pills. An intrauterine device (IUD) can be placed up to 5 days after ovulation, or 5 to 7 days from exposure, and pills can be taken up to 72 hours after exposure. This article discusses hormonal methods, which include combination oral contraception pills, progestin-only pills, gonadotropin-releasing hormone (GnRH) agonists, antiprogestins, the copper IUD, and high-dose estrogen GnRH agonists. Older methods such as danazol are discussed in the context of historical significance.