1背景非意愿妊娠是一个常见的问题。世界上每年约有5千万例流产(van Look 1995)。对这一问题的标准解决方法一直是预防(避孕)，并以人工流产作为补救。但是长期以来在世界上避孕仅仅意味着事先避孕，意外妊娠的一级预防定义应该也必须扩展到事后避孕(Grimes 1997)。紧急避孕是 1 Background Unwanted pregnancy is a common problem. There are about 50 million abortions a year in the world (van Look 1995). The standard solution to this problem has been prevention (contraception), with abortion as a remedy. But for a long time contraception in the world has only meant pre-contraception, and the primary prevention definition of unwanted pregnancies should and should be extended to post-contraception (Grimes 1997). Emergency contraception is