First, the most recent and methodologically sound analyses of the effectiveness of emergency contraception place the typical use effectiveness of the Yuzpe regimen (Preven) at 47 to 53 percent3 and, by extension, the effectiveness of a levonorgestrel (Plan B) regimen at approximately 75 percent,4 both of which are less than the rates quoted by Dr. Weismiller.1
Second, we appreciate Dr. Wellbery's effort to enumerate both sides of the controversial issues around emergency contraception.2 To date, no study has found an actual decrease in pregnancy rates in a population given widespread access to emergency contraception. One study cited by Dr. Weismiller did find a trend toward less consistent use of more reliable contraception in adolescents given advance access to emergency contraception. A full assessment of the public health impact of emergency contraception requires ongoing evidence-based examination, regardless of one’s pre-existing biases.
Third, we agree with Dr. Wellbery's and others' call for appropriate counseling of patients that is sensitive to the patients' moral perspectives.5 The potential for post-fertilization effects of emergency contraception is supported by several lines of medical evidence,6 but in our observation it frequently is minimized or discounted in reference materials for patients. We emphasize that patients deserve full access to this information for adequate informed consent.
in reply: As with many emotionally fraught issues, we must build on the best evidence available. With regard to advance provision of emergency contraception, we know that the use of emergency contraception does not promote sexually careless behavior. Two recent trials1,2 have added to our knowledge of sexual and contraceptive behavior among adolescents who are given emergency contraception. I cite studies involving adolescents because this is an area of greater controversy than adult sexual behavior. In one randomized study,1 emergency contraception use was not associated with changes in unprotected intercourse or less contraceptive use. Another controlled trial2 of 2,117 women 15 to 25 years of age concluded that emergency contraception access has no impact on acquisition of sexually transmitted infections, patterns of contraceptive use, or sexual behavior. Although pregnancy rates in this study did not differ among groups because of high rates of non- emergency contraception use, high rates of unprotected intercourse, and short study duration, these studies at least pave the way for ready access to emergency contraception, a condition that will form the basis for larger population-based studies of pregnancy rates.
The authors also raise the question of post-fertilization effects, and their implications for informed consent. Definitive evidence for the mechanism of action of emergency contraception is lacking, but the most direct evidence from animal and human studies overwhelmingly suggests that the efficacy of emergency contraception relates to the delay and prevention of ovulation.1–3 Of course, additional mechanisms have been proposed, including thickening of cervical mucus, alterations in tubal transport before and after fertilization, and changes in the endometrium.4 How then is a physician to address the issue of mechanism of action? It seems that this is one of those cases where value implications have become unavoidable despite decades of standard practice and family planning benefits. Given the attention forced on this issue, physicians should certainly strive to separate their own values from those of their patients. A discussion of mechanisms of action should include the American College of Obstetricians and Gynecologists’ definition of an established pregnancy, beginning with implantation on the one hand, and personal or religious beliefs related to post-fertilization effects on the other. In the delicate matter of informed consent, one would want a patient to have access to all the information she needs to decide whether she is comfortable using hormonal contraception. At the same time, one would not want to make a patient feel guilty by insisting on moral concerns she does not share.