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Obstetrics/Gynecology
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.
KEY WORDS: contraception, levonorgestrel, postfertilization effect.
Emergency contraception (EC) consists of hormones or postfertilization effect (i.e., early abortion), is important mechanical devices used within 72 hours of sexual in- and could have far-reaching implications given the differ- tercourse with the intent of preventing pregnancy. In the ing attitudes in regard to its use and related issues such as late 1960s and early 1970s, women used high-dose estro- informed consent, emergency department rape protocols, gens such as diethylstilbestrol as EC.1 This treatment was
and conscience clauses. Postfertilization effect refers to replaced in 1974 by combination high-dose oral contra- any effect that reduces the survival rate of the zygote/em- ceptives (OCs) (e.g., ethinyl estradiol/levonorgestrel) used bryo after fertilization, usually prior to clinical recognition within a 12-hour interval (i.e., the Yuzpe regimen) and, in of pregnancy. We use the term early abortion synonymous- later years, by Plan B, which consists of 2 levonorgestrel ly with postfertilization effect. We recognize that some tablets.2 The intrauterine device, danazol (danocrine), and
physicians,4 geneticists, and ethicists have arbitrarily de-
mifepristone have also been studied and promoted as EC, fined human life as beginning after implantation, thereby but the Yuzpe regimen remains the most prevalent form of eschewing the possibility of an early abortion prior to im- EC in the US and Europe.3
plantation. However, we recognize the traditional defini- The question as to whether hormonal EC sometimes tion of pregnancy: “the gestational process, comprising the acts after fertilization to prevent implantation, called a growth and development within a woman of a new indi-vidual from conception through embryonic and fetal peri- Author information provided at the end of the text.
od to birth,” where conception is defined as “the beginning C Kahlenborn et al.
of pregnancy, usually taken to be the instant that a sperma- essary for ovulation, this result has been cited by many as tozoon enters an ovum and forms a viable zygote.”5
evidence that hormonal contraceptive use completely in- In a previous review6 of the mechanism of action of
hibits ovulation. However, the findings of the Carr et al. ar- OCs, we concluded that they act at times via a postfertil- ticle cannot be extrapolated to today’s Yuzpe regimen or ization effect, that is, after fertilization and prior to the clin- Plan B for several reasons. First, although the article was ical recognition of pregnancy. However, the Yuzpe regi- written in 1979, when the doses of estrogen in OCs were men and Plan B have a different dose and time course for higher than the doses in today’s OCs, using high-dose hor- use, which may result in different actions on the reproduc- mones in mid-cycle is far different from using them for 21 tive system. This article reviews data on the use of the days in a 28-day cycle. Second, the findings were based on Yuzpe regimen and Plan B with regard to their mecha- the results of only 4 ovulating women. Therefore, data nisms of action and any potential ethical implications of from that study cannot be used to establish that use of to- day’s OCs or hormonal EC consistently suppresses ovula-tion. Mechanisms of Action
Further data from hormonal assays confirm that EC use does not consistently stop ovulation. One study10 of the
The Physicians’ Desk Reference7 states: “ECPs (Emer-
Yuzpe regimen that examined serum hormonal markers of gency Contraceptive Pills) . . . act primarily by inhibiting ovulation noted that an LH peak concentration occurred ovulation. They may act by altering tubal transport of the within 4 days after the treatment in 5 of 9 women, with a sperm and/or ova and/or altering the endometrium (there- subsequent increase of progesterone, suggesting that ovu- by inhibiting implantation).” The Medical Letter2,8 stated in
lation had occurred. A more recent trial11 using urine hor-
regard to hormonal EC: “Some studies have shown alter- monal markers found an LH peak concentration within 1 ation in the endometrium, suggesting that they could also day of treatment with the Yuzpe regimen in 2 of 8 women, interfere with implantation of the fertilized egg, but other with a subsequent confirmatory increase of progesterone.
studies have found no such effects.” Therefore, the criticalethical questions are: Does use of the Yuzpe regimen or EFFECTS OF HORMONAL EC IN THE PREOVULATORY
Plan B have a postfertilization effect; that is, does hormon- al EC use at times cause an early abortion by altering thereceptive properties of the endometrium? Can such an ef- Table 112-20 notes the major studies that have analyzed
fect occur when EC is used in the preovulatory phase of hormonal EC use. The estimated efficacy rates range from the cycle, or does the postfertilization effect occur only 56.9% to 90.9%, with the largest trial12 showing a 56.9%
when it is used in the ovulatory or postovulatory phase? efficacy rate. The efficacy rate is the percent of reductionin the pregnancy rate of women who used hormonal ECcompared with the estimated rate of women who did not.
EFFECTS ON OVULATION
These rates are calculated from secondary data sources and It is often asserted that hormonal EC use consistently have not been established via a randomized, controlled, stops ovulation. In an early study with oral contraceptives, prospective study (Appendix I3,20-28). This study,12 by the
Carr et al.9 found that a woman’s estradiol, progesterone,
World Health Organization, found that in a group of about luteinizing hormone (LH), and follicle-stimulating hor- 400 women, 6 who used the Yuzpe regimen in the preovu- mone concentrations decreased significantly once she latory phase became pregnant (10 were expected to be- started using OCs. Because an LH surge is presumed nec- come pregnant if no EC was given). In addition, 2 women Table 1. Major Studies on Efficacy Rates of the Yuzpe Regimen of Emergency Contraception
Pregnancya (n)
Reference
Observed
Estimated
Efficacy Rateb (%)
Hertzen and Van Look (1998)12
Webb et al. (1992)13
Zuliani et al. (1990)14
Yuzpe et al. (1982)15
Ho and Kwan (1993)16
Glasier et al. (1992)17
Van Santen and Haspels (1985)18
Percival-Smith and Abercrombie (1987)19
aNumber of actual pregnancies and estimated pregnancies that should have occurred if the Yuzpe regimen had no effect, for each study in which the
Yuzpe regimen was used.
bCalculated efficacy rate based on the observed and estimated pregnancies given in this table (first number) and the efficacy rates based on Trussell’s20
estimates (second percentage figure).
Postfertilization Effect of Hormonal Emergency Contraception
who used Plan B in the preovulatory phase became preg- curred (54 were expected if EC was not given), whereas 7 nant (11 were expected). The preovulatory period is the occurred in the postovulatory phase (11 were expected). In time of the menstrual cycle that occurs more than 3 days the group that used Plan B, 7 pregnancies occurred (53 prior to the expected day of ovulation. The expected day of were expected) in the ovulatory phase, whereas 2 occurred ovulation in this study was estimated as the 14th day prior in the postovulatory phase (10 were expected). These data to the onset of the next menstrual cycle. Although this is an are highly consistent with the hypothesis that hormonal imprecise definition with the potential for significant mis- ECs have a postfertilization effect on the endometrium. In classification, it is the best definition available for these the case of the use of hormonal EC in the ovulatory phase, studies. In addition, Glasier17 presented 2 cases of women
it is still possible that other mechanisms might come into who became pregnant after using the Yuzpe regimen while play (i.e., a change in the viscosity of cervical mucus their progesterone concentrations were <1.5 ng/mL.
and/or an alteration in the tubal transport of either the Therefore, at least 2 studies12,17 have shown that hor-
sperm, ovum, or embryo). However, we could find no data monal EC use, even in the preovulatory phase, does not consistently prevent pregnancy and, by definition, allows
ovulation in those cases. Some have speculated29 that if
Increased Risk of Ectopic Pregnancy?
ovulation is not inhibited, other mechanisms, such as achange in the viscosity of cervical mucus and/or an alter- One result of a postfertilization effect of hormonal EC ation in the tubal transport of sperm, ovum, or embryo, use might be an increased proportion of recognized preg- may come into play. However, there are no clinical data to nancies that are ectopic. If the actions of hormonal ECs on address these theoretical mechanisms. In contrast, there are the fallopian tube and endometrium were such as to have clinical data directly relevant to the potential effects of hor- no postfertilization effects, then the reduction in the rate of intrauterine pregnancies (IUPs) in women taking ECsshould be proportional to the reduction in the rate of ex- EFFECTS ON IMPLANTATION
trauterine pregnancies (EPs) in women taking hormonalECs. However, if the effect of hormonal ECs is to increase OCs are known to adversely affect the implantation pro- the EP/IUP ratio, this would indicate that one or more post- cess,6 which has implications for the Yuzpe regimen and
fertilization effects are operating.6
Plan B because they are composed of the same (or similar) The current proportion of clinical pregnancies that are hormones contained in today’s OCs. OCs affect integrins, ectopic is a little less than 2%.42 In the only study that we
a group of adhesion molecules that have been implicated are aware of regarding hormonal EC and ectopic pregnan- as playing an important role in the area of fertilization and cy, Kubba and Guillebaud43 noted that in 715 women who
implantation. Somkuti et al.30 noted: “These alterations in
used the Yuzpe regimen, 17 pregnancies occurred, including epithelial and stromal integrin expression suggest that im- 1 ectopic pregnancy (i.e., a 5.9% rate of ectopic pregnan- paired uterine receptivity is one mechanism whereby OCs cy), supporting the possibility of one or more postfertiliza- exert their contraceptive action.” In addition, prostaglandins tion effects. However, the confirmation of a postfertiliza- are critical for implantation, but OC use lowers uterine tion effect would take a much larger series of hormonal EC prostaglandin concentrations.31,32 Finally, it is well known
pregnancies to determine whether the proportion of ectopic that OC use decreases the thickness of the endometrium as pregnancies is indeed higher than in those not having used verified by magnetic resonance imaging scans,33,34 and a
thinner endometrium makes implantation more difficult.35-39
Because hormonal EC consists of hormones contained
Relative Contribution of Postfertilization Effect
within OCs, it is possible that the use of hormonal EC hassome of the same effects on the endometrium as does the As noted earlier, 2 small studies10,11 have suggested that
use of OCs. A number of studies support this hypothesis, when EC is given before ovulation, ovulation may be in- noting changes in endometrial histology,1,40 or uterine hor-
hibited in 55–75% of the cases. Under the highly opti- mone receptor levels41 that persist for days after women
mistic assumption that hormonal EC use prevents ovula- used the Yuzpe regimen. All of these findings imply that use tion in 87.5% of women treated, Trussell and Raymond44
of the Yuzpe regimen unfavorably alters the endometrium.
estimated that a mechanism “other than preventing ovula- In addition to the theoretical evidence that EC use ad- tion accounts for 13–38% of the estimated effectiveness of versely affects implantation, Hertzen and Van Look12
the Yuzpe regimen.” This range is higher than 12.5% be- found that both use of the Yuzpe regimen and Plan B re- cause hormonal EC is often used during or after ovulation duced the expected number of pregnancies when they when, by definition, mechanisms other than prevention of were used in the ovulatory phase (17–13 d prior to the next ovulation are in effect. The most likely candidate for the menstrual cycle) and postovulatory phase (≤13 d prior to mechanism “other than preventing ovulation” is a postfer- the expected menstrual cycle), as well as in the preovulato- tilization effect (by effects on the endometrium).
ry phase (as discussed earlier). In the groups that used theYuzpe regimen in the ovulatory phase, 17 pregnancies oc- C Kahlenborn et al.
Summary and Implications
until it is either definitely proven to exist or proven to be acommon event. However, rare but important events are an The evidence to date supports the contention that use of essential part of other informed-consent discussions in EC does not always inhibit ovulation even if used in the medicine, primarily when the rare possibility would be preovulatory phase, and that it may unfavorably alter the judged by the patient to be important. For example, anes- endometrial lining regardless of when in the cycle it is thesia-related deaths are rare for elective surgery; never- used, with the effect persisting for days. The reduced rates theless, it is considered appropriate and legally necessary of observable pregnancy compared with the expected rates to discuss this rare possibility with patients before such in women who use hormonal EC in the preovulatory, ovu- surgery because the possibility of death is so important.
latory, or postovulatory phase are consistent with a postfer- Therefore, for women to whom the induced death of a zy- tilization effect, which may occur when hormonal EC is gote/embryo is important, failure to discuss the possibility used in any of these menstrual phases.
of this loss, even if the possibility is judged to be remote, This interpretation of the cited literature has important would be a failure of informed consent. Furthermore, ramifications, given the polarizing opinions about EC based on the data reviewed in this article, it seems that a use.45 For example, many state laws contain conscience
postfertilization effect is probably more common than is clauses in which medical personnel (e.g., physicians, phar- recognized by most physicians or patients. This is particu- macists, nurses, physician assistants, nurse practitioners) larly true because in the studies done to date, women have cannot be forced to participate in, or refer for, any surgical been more likely to request treatment after intercourse that or drug-induced abortions. Therefore, evidence in favor of occurred near the time of ovulation than after intercourse a postfertilization effect may have legal implications for that occurred earlier in the cycle.44
healthcare providers who either prescribe or have objec- Some have suggested to us that an overemphasis of pos- sible postfertilization effects might make women choose Emergency department protocols could also be impact- not to use EC and therefore increase the incidence of un- ed by evidence of a postfertilization effect. For example, planned pregnancies. Both of these views fail to acknowl- emergency departments of Catholic hospitals usually allow edge the value of a woman’s right to make decisions based either no use of hormonal EC in their rape protocols or on informed consent. During informed-consent discus- limited use (i.e., preovulatory use of hormonal EC).45
sions, overemphasis of any single possible risk may not re- Catholic hospitals that do allow hormonal EC use prior to sult in appropriate informed consent; however, failing to ovulation may wish to reassess their policies given the mention a possible risk would be a failure of adequate in- findings that EC use does not consistently stop ovulation formed consent. Therefore, discussion of a potential post- and has the potential of causing a postfertilization effect fertilization risk should occur and should be kept within even when used prior to ovulation. Most large secular hos- the perspective of the available medical evidence.
pitals have fewer limitations on the use of hormonal EC as Proper informed consent requires patient and physician part of their rape protocols. Nevertheless, evidence of a comprehension of information, the disclosure of that infor- postfertilization effect from use of hormonal EC is impor- mation, and the sharing of interpretations. If a postfertiliza- tant to physicians who must make a moral decision about tion mechanism of hormonal EC use violates the morals of prescribing or referring for a drug that can cause an early any woman, the failure of the physician or care provider to disclose that information would effectively eliminate the There are potential limitations in our conclusions. Be- likelihood that the woman’s consent was truly informed.
cause no controlled trials have been done with women us- Finally, there is in our view a potential for negative psy- ing EC, our conclusions are based on the existing data of chological impact on women who value human life from case series with historical controls. However, these are the conception onward, and have not been given informed best available data for hormonal EC use. In addition, we consent about hormonal EC use, and later learn of the po- have assumed, based on our discussions with physicians tential postfertilization effects. Their responses could in- and laypeople across the country, that a significant number clude disappointment, guilt, sadness, anger, rage, depres- of physicians and patients would be concerned about a sion, or a sense of having been violated by the provider. To possible postfertilization effect. Although some evidence assume that all patients will not care about a postfertiliza- does exist to support our assumption,45,46 further research is
tion effect is not supported by the literature.45,47-49
needed. Nevertheless, the principle of informed consentwould state that it is important to inform women who may Chris Kahlenborn MD, Department of Internal Medicine, Altoona
use hormonal EC about this possible effect so that they can Hospital, Altoona, PA; Department of Internal Medicine, Bon Sec-our Hospital, Altoona, E-mail kahlen@alt3.com choose based on the best available data.
Joseph B Stanford MD MSPH, Assistant Professor, Department
Regardless of the personal beliefs of the physician or of Family and Preventive Medicine, University of Utah, Salt Lake provider about the mechanism of hormonal EC use, it is important that patients have information relevant to their Walter L Larimore MD, Associate Clinical Professor, Community
and Family Medicine, University of South Florida, Tampa, FL
own beliefs and value systems. It has been suggested to us Reprints available from The Annals of Pharmacotherapy by some that postfertilization loss attributed to hormonalEC use would not need to be included in informed consent We thank Dorothy Dugandzic BS and Walt Severs PhD for their technical assistance.
Postfertilization Effect of Hormonal Emergency Contraception
References
Appendix I. Critique of EC Efficacy
1. Yuzpe AA, Thurlow HJ, Ramzy I, Leyshon JI. Post coital contraception — a pilot study. J Reprod Med 1974;13:53-8.
The measure of efficacy is critical to an analysis of a possible post- 2. Plan B: a progestin only contraceptive. Med Lett 2000;42:10.
fertilization effect. For example, if hormonal EC use had a 0% effica- 3. LaValleur J. Emergency contraception. Obstet Gynecol Clin North Am cy rate, the question of a postfertilization effect would be irrelevant.
Hormonal EC use received Food and Drug Administration approval 4. Hughes EC, ed. Committee on terminology, American College of Obste- without evidence of a randomized, controlled, prospective study re- tricians and Gynecologists. Obstetric–gynecological terminology. Philadel- garding its effectiveness.3,21 Rather, effectiveness was estimated
based on the studies we have reviewed in this article. We noted the 5. Mosby’s medical, nursing, & allied health dictionary. 6th ed. Philadel- efficacy rates based on the raw data versus Trussell et al.’s20 calcu-
lated estimates for each of the 8 trials presented in Table 1. Trussellet al. used the latter estimates to calculate an overall efficacy rate of 6. Larimore WL, Stanford J. Postfertilization effects of oral contraceptives 74.1%, while the raw data yield a figure of 65.7%.
and their relationship to informed consent. Arch Fam Med 2000;9:126-33.
In these studies, the pregnancy rates of the cohort were compared 7. Physicians’ desk reference. 54th ed. Montvale, NJ: Medical Economics, with pregnancy rates estimated from historical controls. Specifically, the control pregnancy rates were based on the procedure developed 8. An emergency contraceptive kit. Med Lett 1998;40:102-3.
in the Dixon Study,22 which estimated the expected rate of pregnan-
9. Carr BR, Parker CR, Madden JM, MacDonald PA, Porter JC. Plasma cy in women from a single act of intercourse on a particular day of levels of adrenocorticotropin and cortisol in women receiving oral con- the menstrual cycle. Dixon based the probability of pregnancy per traceptive steroid treatment. J Clin Endocrinol Metab 1979;49:346-9.
specific day on 2 major studies: Schwartz et al. (1979)23 and Barrett
10. Ling WY, Robichaud A, Zayid I, Wrixon W, MacLeod SC. Mode of ac- and Marshall (1969).24 In subsequent analyses, Trussell et al.
tion of dl-norgestrel and ethinylestradiol combination in postcoital con- dropped the Schwartz study, which was based on artificial insemina- traception. Fertil Steril 1979;32:297-302.
tion, and added another historical control group from a cohort of 11. Swahn LM, Westlund P, Johannisson E, Bygdeman M. Effect of post- women trying to achieve pregnancy in North Carolina in the early coital contraceptive methods on the endometrium and the menstrual cy- 1980s.25 In doing this, Trussell et al. were in fact not comparing con-
cle. Acta Obstet Gynecol Scand 1996;75:738- 44.
temporaneous cohorts and controls. This major design problem may 12. Hertzen H, Van Look PFA. Randomised controlled trial of levonorgestrel render the conclusions of the studies uncertain for 2 reasons: versus the Yuzpe regimen of combined oral contraceptives for emergen-cy contraception. Lancet 1998;352:428-33.
1. In the 1960s, the rate of infertility was lower than in later years.
For example, “infertility increased 177% among married women 13. Webb AMC, Russell J, Elstein M. Comparison of Yuzpe regimen, dana- aged 20 to 24 years between 1965 and 1982.”26 Therefore, the
zol, and mifepristone (RU 486) in oral postcoital contraception. BMJ rate of infertility would be expected to be lower for the Barrett controls than for the study cohorts (women using EC). In addition, 14. Zuliani G, Colombo UF, Molla R. Hormonal postcoital contraception Wilcox et al.25 noted that “women were excluded if they had a se-
with an ethinylestradiol–norgestrel combination and two danazol regi- rious chronic illness or if they or their partners had a history of fer- mens. Eur J Obstet Gynecol Reprod Biol 1990;37:253-60.
tility problems.” None of the case studies reported specifically 15. Yuzpe AA, Smith RP, Rademaker AW. A multicenter clinical investiga- screening for infertility. It is therefore probable that both of the his- tion employing ethinyl estradiol combined with dl-norgestrel as a post- torical control studies had a lower rate of infertility than the case coital contraceptive agent. Fertil Steril 1982;37:508-13.
studies. If this is true, then studies of EC use that employ histori- 16. Ho PC, Kwan MSW. A prospective randomized comparison of levo- cal controls for comparison may overestimate the effectiveness of norgestrel with the Yuzpe regimen in post-coital contraception. Hum Re- EC use in preventing or ending a pregnancy.
17. Glasier A, Thong KJ, Dewar M, Mackie M, Baird DT. Mifepristone 2. Selecting controls from women who were not seeking to use EC (RU- 486) compared with high-dose estrogen and progestogen for emer- to avoid pregnancy may lead to differences that could affect the gency postcoital contraception. N Engl J Med 1992;327:1041- 4.
results. For example, some controls came from the Barrett and 18. Van Santen MR, Haspels AA. A comparison of high-dose estrogens ver- Marshall study,24 which examined 241 couples who were using a
sus low-dose ethinylestradiol and norgestrel combination in postcoital natural family planning method based on basal body tempera- interception: a study in 493 women. Fertil Steril 1985;43;206-13.
ture. Some of these women were trying to conceive, as were the 19. Percival-Smith RK, Abercrombie B. Postcoital contraception with dl- women enrolled in the Wilcox et al. trial.25 None was known to be
norgestrel/ethinyl estradiol combination: six years experience in a stu- under the stress of a rape or other high-stress situation. However, dent medical clinic. Contraception 1987;36:287-93.
the cohort in the 8 trials cited by Trussell were trying to prevent or 20. Trussell J, Rodriguez G, Ellertson C. Updated estimates of the effective- end their pregnancy and were probably under more emotional ness of the Yuzpe regimen of emergency contraception. Contraception stress than the controls who desired pregnancy. If 2 groups of women are examined, one that desires pregnancy and the other 21. Glasier A. Emergency contraception. Br Med Bull 2000;56:729-38.
that does not and is under stress, the fertility rates in each groupmay vary markedly because it is possible that under extreme 22. Dixon GW, Schlesselman JJ, Ory HW, Blye RP. Ethinyl estradiol and stress, the secretion of ovulatory hormones from the pituitary conjugated estrogens as postcoital contraceptives. JAMA 1980;244: gland could be inhibited. For example, Diamond27 noted a
prospective study in Minnesota of 4000 women who had been 23. Schwartz D, Mayaux MJ, Martin-Boyce A, Czyglik F, David G. Donor raped and none had become pregnant. This may reflect an en- insemination: conception rate according to cycle day in a series of 821 dogenous hormonal change whereby the women’s bodies inhibit- cycles with a single insemination. Fertil Steril 1979;31:226-9.
ed ovulation during or shortly after the time of the sexual assault.
24. Barrett JC, Marshall J. The risk of conception on different days of the menstrual cycle. Popul Stud 1969;23:455-61.
3. All of the EC studies are based on a fixed timing of ovulation rela- 25. Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in re- tive to cycle length (e.g., 14 d before the next menstrual cycle).
lation to ovulation. Effects on probability of conception, survival of the However, the length of the luteal phase varies significantly, both pregnancy, and sex of baby. N Engl J Med 1995;333:1517-21.
between women, and to a lesser extent, within the same woman, 26. Hacker NF, Moore JG. Essentials of obstetrics and gynecology. 3rd ed.
even for women of regular cycles.28 Therefore, the assignment of
conception probabilities based on day relative to ovulation is im- 27. Diamond EF. Ovral in rape protocols. Ethics Medics 1996;21(10):2.
28. Wilcox AJ, Dunson D, Baird DD. The timing of the “fertile window” in the menstrual cycle: day specific estimates from a prospective study.
We believe for the above-noted reasons that the estimates of effica- cy rates for hormonal EC use are highly tentative and require further 29. Glasier A. Emergency postcoital contraception. N Engl J Med 1997;337: C Kahlenborn et al.
30. Somkuti SG, Sun J, Yowell C, Fritz M, Lessey B. The effect of oral con- traceptive pills on markers of endometrial receptivity. Fertil Steril 1996: OBJETIVO: Evaluar la posibilidad de un efecto de post-fertilización con
relación a los tipos de contracepción hormonal de emergencia más 31. Dawood YM. Ibuprofen and dysmenorrhea. Am J Med 1984;77(1A):87- comúnes utilizados en los EU, y explorar el impacto ético de esta 32. Bieglmayer C, Hofer G, Kainz C, Reinthaller A, Kopp B, Janisch H.
Concentration of various arachidonic acid metabolites in menstrual fluid FUENTES DE INFORMACIÓN: Se realizó una búsqueda en MEDLINE del
are associated with menstrual pain and are influenced by hormonal con- 1966 a noviembre 2001 con el propósito de identificar todos los traceptives. Gynecol Endocrin 1995;9:307-12.
artículos pertinentes en el idioma inglés. Una revisión de las secciones 33. Brown HK, Stoll BS, Nicosia SV, Fiorica JV, Hambley PS, Clarke LP, et de referencia de los artículos de revisión principales se realizó para al. Uterine junctional zone: correlation between histiologic findings and MR imaging. Radiology 1991;179:409-13.
SÍNTESIS: Los tipos más comúnes de contracepción hormonal de
34. Demas BE, Hricak H, Jaffe RB. Uterine MR imaging: effects of hor- emergencia utilizados en los EU son el régimen Yuzpe (dosis alta de monal stimulation. Radiology 1986;159:123-6.
etînil-estradiol con dosis alta de levonorgestrel) y Plan B (dosis alta de 35. Abdalla HI, Brooks AA, Johnson MR, Kirkland A, Thomas A, Studd levonorgestrel sólo). Aunque ambos métodos en ocasiones detienen la JW. Endometrial thickness: a predictor of implantation in ovum recipi- ovulación, también podrían actuar reduciendo la posibilidad de implantación debido a su efecto adverso en el endometrio (un efecto de 36. Dickey RP, Olar TT, Taylor SN, Curole DN, Matulich EM. Relationship post-fertilización). La evidencia disponible para un efecto de post- of endometrial thickness and pattern to fecundity in ovulation induction fertilización es moderadamente fuerte, ya sea que se utilize la cycles: effect of clomiphene citrate alone and with human menopausal contracepción hormonal de emergencia en la fase pre-ovulatoria, gonadotropin. Fertil Steril 1993;59:756-60.
ovulatoria, o post-ovulatoria del ciclo menstrual.
37. Gonen Y, Casper RF, Jacobson W, Blankier J. Endometrial thickness and growth during ovarian stimulation: a possible predictor of implantation CONCLUSIONES: En base a la evidencia teórica y empírica presente,
in in-vitro fertilization. Fertil Steril 1989;52:446-50.
ambos el régimen Yuzpe y el Plan B, probablemente actúan en 38. Schwartz LB, Chiu AS, Courtney M, Krey L, Schmidt-Sarosi C. The ocasiones causando un efecto de post-fertilización independientemente embryo versus endometrium controversy revisited as it relates to predict- de cuándo, durante el ciclo menstrual, son utilizados. Estos hallazgos ing pregnancy outcome in in-vitro fertilization — embryo transfer cy- tienen implicaciones potenciales en tales áreas como el consentimiento educado, los protocolos de salas de emergencia y las cláusulas de 39. Shoham Z, Carlo C, Patel A, Conway GS, Jacobs HS. Is it possible to run a succesful ovulation induction program based solely on ultrasoundmonitoring: the importance of endometrial measurements. Fertil Steril 40. Ling WY, Wrixon W, Zayid I, Acorn T, Popat R, Wilson E. Mode of ac- tion of dl-norgestrel and ethinylestradiol combination in postcoital con-traception. II. Effect of postovulatory administration on ovarian function OBJECTIF: Évaluer les effets des médicaments permettant une
and endometrium. Fertil Steril 1983;39:292-7.
contraception orale d’urgence sur la fécondation et discuter les 41. Kubba AA, White JO, Guillebaud J, Elder MG. The biochemistry of hu- répercussions éthiques de ces effets.
man endometrium after two regimens of postcoital contraception: a dl- REVUE DE LITTÉRATURE ET SÉLECTION DES ÉTUDES: Recherche de la base
norgestrel/ethinylestradiol combination or danazol. Fertil Steril 1986;45: de données MEDLINE (1966 à novembre 2001) des articles pertinents de langue anglaise et revue systématique de la bibliographie des articles 42. Aboud A. A five-year review of ectopic pregnancy. Clin Exp Obstet Gy- RÉSUMÉ DES DONNÉES: Les deux régimes les plus fréquemment utilisés
43. Kubba AA, Guillebaud J. Case of ectopic pregnancy after postcoital con- aux États-Unis pour la contraception orale d’urgence sont celui de traception with ethinyloestradiol–levonorgestrel. Br Med J 1983;287:1343- 4.
Yuzpe (hautes doses d’éthinylestradiol et de lévonorgestrel) et celui duPlan B (hautes doses de lévonorgestrel). La principale action 44. Trussell J, Raymond EG. Statistical evidence about the mechanism of ac- tion of the Yuzpe regimen of emergency contraception. Obstet Gynecol pharmacologique de ces 2 régimes semble être associée à leur pouvoir inihibiteur de l’ovulation. Cependant, il semble qu’ils aient aussi un effet 45. Golden NH, Seigel WM, Fisher M, Schneider M, Quijano E, Suss A, et au niveau de l’endomètre, interférant ainsi l’implantation de l’ovule al. Emergency contraception: pediatricians’ knowledge, attitudes and fécondée. Plusieurs études font état de cette dernière action opinions. Pediatrics 2001;107:287-92.
pharmacologique et ce, indépendamment de la période du cycle 46. Spinnato JA. Mechanism of action of intrauterine contraceptive devices menstruel durant laquelle ces régimes sont donnés (phase pré- ou post- and its relation to informed consent. Am J Obstet Gynecol 1997;176: CONCLUSIONS: En plus d’inihiber l’ovulation, la contraception orale
47. Wilkinson J. Ethical problems at the beginning of life. In: Wilkinson J, d’urgence semble altérer les propriétés de l’endomètre pouvant causer ed. Christian ethics in health care: a source book for Christian doctors, ainsi un avortement précoce. Considérant cet effet pharmacologique nurses and other health care professionals. Edinburgh, Scotland: Handsel potentiel, l’administration de la contraception orale d’urgence soulève alors certains aspects éthiques quant à l’obtention d’un consentement 48. Ryder RE. Natural family planning: effective birth control supported by éclairé de la patiente, quant à l’implantation systématique de protocoles the Catholic Church. BMJ 1993;307:723-6.
dans les salles d’urgence et quant à la responsabilité éthique des 49. Tonti-Filippini N. The pill: abortifacient or contraceptive: a literature re- professionnels de la santé prescrivant et administrant cette médication.
view. Linacre Quarterly 1995;Feb:5-28.

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