The Annals of Pharmacotherapy: Vol. 36, No. 3, pp. 465–470.

Postfertilization Effect of Hormonal Emergency Contraception
Chris Kahlenborn, Joseph B Stanford, and Walter L Larimore

OBJECTIVE: To assess the possibility of a postfertilization effect in regard to the most common types of hormonal emergency contraception (EC) used in the US and to explore the ethical impact of this possibility.

DATA SOURCES AND STUDY SELECTION: A MEDLINE search (1966–November 2001) was done to identify all pertinent English-language journal articles. A review of reference sections of the major review articles was performed to identify additional articles. Search terms included emergency contraception, postcoital contraception, postfertilization effect, Yuzpe regimen, levonorgestrel, mechanism of action, Plan B.

DATA SYNTHESIS: The 2 most common types of hormonal EC used in the US are the Yuzpe regimen (high-dose ethinyl estradiol with high-dose levonorgestrel) and Plan B (high-dose levonorgestrel alone). Although both methods sometimes stop ovulation, they may also act by reducing the probability of implantation, due to their adverse effect on the endometrium (a postfertilization effect). The available evidence for a postfertilization effect is moderately strong, whether hormonal EC is used in the preovulatory, ovulatory, or postovulatory phase of the menstrual cycle.

CONCLUSIONS: Based on the present theoretical and empirical evidence, both the Yuzpe regimen and Plan B likely act at times by causing a postfertilization effect, regardless of when in the menstrual cycle they are used. These findings have potential implications in such areas as informed consent, emergency department protocols, and conscience clauses.

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The text below is only an extract of the section titled SUMMARY AND IMPLICATIONS:
The evidence to date supports the contention that use of EC does not always inhibit ovulation even if used in the preovulatory phase, and that it may unfavorably alter the endometrial lining regardless of when in the cycle it is used, with the effect persisting for days. The reduced rates of observable pregnancy compared with the expected rates in women who use hormonal EC in the preovulatory, ovulatory, or postovulatory phase are consistent with a postfertilization effect, which may occur when hormonal EC is used in any of these menstrual phases.

This interpretation of the cited literature has important ramifications, given the polarizing opinions about EC use.
For example, many state laws contain conscience clauses in which medical personnel (e.g., physicians, pharmacists, nurses, physician assistants, nurse practitioners) cannot be forced to participate in, or refer for, any surgical or drug-induced abortions. Therefore, evidence in favor of a postfertilization effect may have legal implications for healthcare providers who either prescribe or have objections to prescribing these agents.

Emergency department protocols could also be impacted by evidence of a postfertilization effect. For example, emergency departments of Catholic hospitals usually allow either no use of hormonal EC in their rape protocols or limited use (i.e., preovulatory use of hormonal EC). Catholic hospitals that do allow hormonal EC use prior to ovulation may wish to reassess their policies given the findings that EC use does not consistently stop ovulation and has the potential of causing a postfertilization effect even when used prior to ovulation. Most large secular hospitals have fewer limitations on the use of hormonal EC as part of their rape protocols. Nevertheless, evidence of a postfertilization effect from use of hormonal EC is important to physicians who must make a moral decision about prescribing or referring for a drug that can cause an early abortion.

There are potential limitations in our conclusions. Because no controlled trials have been done with women using EC, our conclusions are based on the existing data of case series with historical controls. However, these are the best available data for hormonal EC use. In addition, we have assumed, based on our discussions with physicians and laypeople across the country, that a significant number of physicians and patients would be concerned about a possible postfertilization effect. Although some evidence does exist to support our assumption, f
urther research is needed. Nevertheless, the principle of informed consent would state that it is important to inform women who may use hormonal EC about this possible effect so that they can choose based on the best available data.

Regardless of the personal beliefs of the physician or provider about the mechanism of hormonal EC use, it is important that patients have information relevant to their own beliefs and value systems. It has been suggested to us by some that postfertilization loss attributed to hormonal EC use would not need to be included in informed consent until it is either definitely proven to exist or proven to be a common event. However, rare but important events are an essential part of other informed-consent discussions in medicine, primarily when the rare possibility would be judged by the patient to be important. For example, anesthesia-related deaths are rare for elective surgery; nevertheless, it is considered appropriate and legally necessary to discuss this rare possibility with patients before such surgery because the possibility of death is so important. Therefore, for women to whom the induced death of a zygote/embryo is important, failure to discuss the possibility of this loss, even if the possibility is judged to be remote, would be a failure of informed consent. Furthermore, based on the data reviewed in this article, it seems that a postfertilization effect is probably more common than is recognized by most physicians or patients. This is particularly true because in the studies done to date, women have been more likely to request treatment after intercourse that occurred near the time of ovulation than after intercourse that occurred earlier in the cycle.

Some have suggested to us that an overemphasis of possible postfertilization effects might make women choose not to use EC and therefore increase the incidence of unplanned pregnancies. Both of these views fail to acknowledge the value of a woman's right to make decisions based on informed consent. During informed-consent discussions, overemphasis of any single possible risk may not result in appropriate informed consent; however, failing to mention a possible risk would be a failure of adequate informed consent. Therefore, discussion of a potential postfertilization risk should occur and should be kept within the perspective of the available medical evidence.

Proper informed consent requires patient and physician comprehension of information, the disclosure of that information, and the sharing of interpretations. If a postfertilization mechanism of hormonal EC use violates the morals of any woman, the failure of the physician or care provider to disclose that information would effectively eliminate the likelihood that the woman's consent was truly informed.

Finally, there is in our view a potential for negative psychological impact on women who value human life from conception onward, and have not been given informed consent about hormonal EC use, and later learn of the potential postfertilization effects. Their responses could include disappointment, guilt, sadness, anger, rage, depression, or a sense of having been violated by the provider. To assume that all patients will not care about a postfertilization effect is not supported by the literature.