Objective To re-estimate the efficacy of emergency contraceptive pills (ECPs) by new Wilcox method in contrast to Dixon method.
Methods By employing data from two recent published clinical trials of emergency contraception (Trial Ⅰ from the randomized controlled studies on mifepriston with small doses and levonorgestrel for emergency contraception, and Trial Ⅱ from the relative bioavailability of levonorgestrel for emergency contraception), we re-examined the effectiveness of the two ECPs regimen using new estimates of conception probabilities by cycle day relative to the first day of bleeding (new Wilcox method) at Family Planning Research Institute of Tongji Medical College, Huazhong University of Science and Technology from August 2000 to March 2002. Results In contrast to Dixon method, the effective rates in Trial Ⅰ dropped from 88.29% to 83.29% in treatment group, and from 89.13% to 83.57% in contrast controls,respectively, by the new Wilcox method. Similarly, the effective rates in Trial Ⅱ dropped from 72.66% to 64.35% in contrast controls, and remained the same in treatment group for lacking of the occurrence of pregnancy. Conclusion Our results suggest that the Dixon method probably overstated the effectiveness of ECPs when based on conception probabilities by cycle day relative to day of ovulation.