THE EFFECTIVENESS OF POSTCOITAL HORMONAL CONTRACEPTION

The authors of a literature review of 10 studies on the efficacy of postcoital hormonal contraception (PCHC) contend that the studies' failure rates were too low because they divided the number of observed pregnancies by total number of women treated with PCHC. They claim that the only significant measure of efficacy is proportionate reduction in pregnancies caused by PCHC. Further, they examined the number of observed pregnancies and expected pregnancies if the women had not used PCHC. 2 different methods to estimate expected number of pregnancies resulted in 2 sets of failure rates for combined estrogen preparations (CEP): 4.2-100% and 5.9-44.4%. 2 other professionals find their use of Tietze's pregnancy risk estimates inapplicable, because women who use PCHC do not experience uniform distribution of unprotected intercourse across the cycle but rather near midcycle. Thus, their assumption of 2-4% risk of pregnancy per single unprotected act of intercourse biases the results. These professionals consider that the way to compare results from different studies is to use expected number of pregnancies estimated by corresponding the cycle day of intercourse with cycle day specific conception rates to obtain the only significant estimates of PCHC efficacy. Yet this methodology was applied in only 4 of the 10 studies examined by the authors of the literature review. Further, 1 study used a high-dose estrogen and 3 used a CEP preparation. Effectiveness rates were 84% for the high-dose estrogen and a mean of 76% for the 3 CEP studies. Further, there were 3 other CEP studies published after the literature review which had used the appropriate methodology. The weighted average of the 5 literature review CEP studies and these 3 studies is 74.%. Even though PCHC is not perfectly effective, it does adequately protect against unintended pregnancy. RU-486 is more effective than CEPs, but until it is available in the US, the best means of preventing unplanned pregnancies after intercourse is PCHC.