Plan B: Not an Abortifacient?

By Dr. Jeff Mirus ( bio - articles - email ) | Dec 19, 2007

I am indebted to a reader knowledgeable in biology for sending me a study from the latest (Winter 2007) issue of The National Catholic Bioethics Quarterly questioning whether Plan B is an abortifacient. This is an important follow-up to my recent column on Plan B and the Case of Rape.

The assumption that Plan B acts as an abortifacient is drawn primarily from the manufacturer’s literature, which states: “This product works mainly by preventing ovulation. It may also prevent fertilization of a released egg or attachment of a fertilized egg to the uterus” (emphasis added). In addition, a number of studies of Plan B over the past decade have suggested that the drug has an abortifacient effect. These studies argue both that this is theoretically consistent with the operation of other oral contraceptives (which decrease the thickness of the lining of the uterus) and that it is statistically consistent with a decrease in successful pregnancies even after the putative occurrence of ovulation.

In a new survey of the available evidence (“Is Plan B an Abortifacient? A Critical Look at the Scientific Evidence”), Providence College biology professor Rev. Nicanor Pier Giorgio Austriaco, OP writes that these assumptions may be offset by new work in 2007 which strongly suggests that Plan B is not an abortifacient after all. One newer study has corrected a methodological flaw in the older studies which strongly suggests they were inaccurate on the question of when ovulation occurred. Another new study has directly measured the ability of embryos to implant and found that Plan B does not affect this ability. Both studies conclude that Plan B has no measurable post-fertilization effect, and Fr. Austriaco notes that this conclusion is consistent with larger studies among animals.

Fr. Austriaco cautions that both of the new studies involved very small groups of women, and that larger studies with more stringent protocols are needed to “obtain the most accurate data on both the efficacy and the mode of action of Plan B”. Nonetheless, if these newest studies are a reliable guide, the Connecticut Bishops cannot be faulted for administering Plan B without an ovulation test in cases of rape.

One might wish that the Bishops had more clearly explained their decision, instead of merely referring to “doubt” about how Plan B works. Nonetheless, as I commented in my column, “It is important to recognize that an accurate understanding of the way Plan B works is critical to the analysis,” which heavily “depends on prudential judgments based on human expertise.” To the precise degree that the manufacturer’s claim that Plan B “may” prevent implantation can be dismissed, the moral case for the use of Plan B in all cases of rape is strengthened.