Significantly, in light of this evidence, the International Federation of Gynecology & Obstetrics (FIGO) and the International Consortium for Emergency Contraception – which admittedly are not pro-life or Catholic organizations – conclude the following:
- Inhibition or delay of ovulation is LNG ECPs principal and possibly only mechanism of action.
- Review of the evidence suggests that LNG ECPs cannot prevent implantation of a fertilized egg. Language on implantation should not be included in LNG ECP product labeling.
- The fact that LNG ECPs have no demonstrated effect on implantation explains why they are not 100% effective in preventing pregnancy, and are less effective the later they are taken. Women should be given a clear message that LNG ECPs are more effective the sooner they are taken.
- LNG ECPs do not interrupt a pregnancy (by any definition of the beginning of pregnancy). However, LNG ECPs can prevent abortions by reducing unwanted pregnancies.
Clearly, one can quibble about the limitations and flaws of a particular study or a particular research approach – and biologists do this routinely – but what is impressive, in my view, is the cumulative data from a growing number of independent research groups using different methods and study protocols, which together lead to the research findings summarized by FIGO and ICEC.
Of interest, the primary findings of the FIGO and ICEC white paper echo the conclusions of three other recent scientific reviews of the mechanism of action of LNG, which also conclude that the drug does not have a post-fertilization effect when it is used as an emergency contraceptive.[13]
In light of this data, I propose that the scientific evidence shows that not all morning-after pills are abortifacients. Friday, I will address the concerns of some of my critics who have suggested that Plan B may be an abortifacient if it is taken during the first three days of the “fertile window” prior to ovulation.
Read part 1 of this series here. The next article in this series will explore the scientific evidence that indicates Plan B causes early abortions if administered during the “fertile window.” Read part 3 here.
[1] J.A. Keenan, “Ulipristal acetate: contraceptive or contragestive?” Ann Pharmacother 45 (2011): 813-815.
[2] U.S. Food and Drug Administration: http://www.fda.gov/drugs/drugsafety/postmarketdrugsafetyinformationforpatientsandproviders/ucm111323.htm.
[3] “Is Plan B an Abortifacient? A Critical Look at the Scientific Evidence,” National Catholic Bioethics Quarterly 7 (2007): 703-707. For critiques of my position and my reply, see Marie T. Hilliard, “Plan B’s Abortifacient Effect,” NCBQ 8 (2008): 9-13; and Patrick Yeung, Jr., Erica Laethem, and Joseph Tham, LC “Is Plan B Abortifacient? Further Responses,” NCBQ 8 (2008): 217-221.
[4] The bulk of the analysis that follows is based on my letter to the editor, “Scientific Certitude, Moral Certitude, and Plan B,” NCBQ 11 (2011): 623-627. I thank Dr. Ted Furton, editor-in-chief of the NCBQ for permission to reproduce significant portions of that letter here.
[5] International Federation of Gynecology & Obstetrics (FIGO) and the International Consortium for Emergency Contraception, “March 2011: Mechanism of Action – How Do Levonorgestrel-only Emergency Contraceptive Pills (LNG ECPs) Prevent Pregnancy?” Available at www.cecinfo.org/UserFiles/File/MOA_FINAL_2011_ENG.pdf. Last accessed on August 16, 2011.
[6] Noe et al., “Contraceptive Efficacy of Emergency Contraception with Levonorgestrel Given Before or After Ovulation,” Contraception 81 (2010): 414-420; Novikova et al., “Effectiveness of Levonorgestrel Emergency Contraception Given Before or After Ovulation – A Pilot Study,” Contraception 75 (2007): 112-118.
[7] Marions et al., “Emergency Contraception with Mifepristone and Levonorgestre: Mechanism of Action,” Obstetrics and Gynecology 100 (2002): 65-71; del Carmen Cravioto et al., “On the Mechanisms of Action of Short-Term Levonorgestrel Administration in Emergency Contraception,” Contraception 64 (2001): 227-234; Meng et al., “Effect of Levonorgestrel and Mifepristone on Endometrial Receptivity Markers in a Three-Dimensional Human Endometrial Cell Culture Model. Fertility and Sterility 91 (2009): 256-64; Meng et al., “Effects of Oral and Vaginal Administration of Levonorgestrel Emergency Contraception on Markers of Endometrial Receptivity,” Human Reproduction 25 (2010): 874-883; Palomino et al., “A Single Midcycle Dose of Levonorgestrel Similar to Emergency Contraceptive Does Not Alter the Expression of the L-selectin Ligand or Molecular Markers of Endometrial Receptivity. Fertility and Sterility 94 (2010): 1589-1594.
[8] Meng et al., Human Reproduction 25 (2010): 874-883.
[9] Durand et al., “Late Follicular Phase Administration of Levonorgestrel as an Emergency Contraceptive Changes the Secretory Pattern of Glycodelin in Serum and Endometrium During the Luteal Phase of the Menstrual Cycle. Contraception 71(2005): 451-457.
[10] Lalitkumar et al., “Mifepristone, but not Levonorgestrel, Inhibits Human Blastocyst Attachment to an In Vitro Endometrial Three-dimensional Cell Culture Model. Human Reproduction 22 (2007): 3031-3037.
[11] Müller et al., “Postcoital Treatment with Levonorgestrel Does Not Disrupt Postfertilization Events in the Rat,” Contraception 67 (2003): 415-419; Ortiz et al. “Post-coital Administration of Levonorgestrel Does Not Interfere with Post-fertilization Events in the New World Monkey Cebus paella,” Human Reproduction 19 (2004): 1352-1356.
[12] Zhang et al., “Pregnancy Outcome After Levonorgestrel-only Emergency Contraception Failure: A Prospective Cohort Study,” Human Reproduction 24 (2009): 1605-1611; De Santis et al., “Failure of the Emergency Contraceptive Levonorgestrel and the Risk of Adverse Effects in Pregnancy and on Fetal Development: An Observational Cohort Study,” Fertility and Sterility 84 (2005): 296-299.
[13] Kristina Gemzell-Danielsson, “Mechanism of Action of Emergency Contraception,” Contraception 82 (2010): 404-409; Leung et al., “Mechanisms of Action of Hormonal Emergency Contraception,” Pharmacotherapy 30 (2010): 158-168; Gemzell-Danielsson et al., “Emergency Contraception – Mechanisms of Action,” Contraception 87 (2013): 300-308.
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