1Dixon G W, Schiesselman J J, Ory. H W, et al. Ethinyl estradiol and conjugated estrogens as postcoital contraceptives[J].JAMA, 1980, 244: 1336.
2Task Force on Postovulatory Methods of Fertility Regulation. Randomised controlled trial of levonorgestrel versus the Yuzpe regimen of combined oral contraceptives for emergency contraception[Jl. Lancet, 1998, 352: 428.