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The facts on Plan B

Letter to the Editor | Wednesday, November 8, 2006

In order to form an opinion about Plan B, I must rely on the reports of researchers and drug companies. The evidence I have seen, including both reports cited in Dan Hicks’s last letter, does not seem to prove that Plan B is not abortifacient (“Plan B”, Nov. 6).

The first source cited by Hicks provides the most promising evidence for his assertion that Plan B is not abortifacient. This report discusses an experiment conducted on monkeys. Plan B was given to these monkeys after having sex during an ovulatory period. The number of times an embryo implanted in the womb of a monkey was roughly the same for those monkeys who were and were not taking Plan B. Although this statistical similarity is suggestive, it does not tell us anything about the mechanisms that caused the failure of implantation in those monkeys who were taking Plan B. Different causes can achieve a similar outcome a similar number of times.

This same source also provides a report about a study done on a group of women, who attempted to take Plan B during their preovulatory fertile period. 82 percent of the women taking Plan B did not ovulate for up to five days. Clearly these women, if sexually active during this time, would not have become pregnant – regardless of whether pregnancy begins at conception or implantation. Taking Plan B did not prevent ovulation for 18 percent of the women in the study. One of the researchers says: “We conclude that the effects exerted by Plan B, when it is taken before the onset of LH surge [i.e., before ovulation], may fully explain the pregnancies averted by emergency contraception. Failure to affect the LH surge, because treatment was begun too late in the fertile preovulatory period, explains the 20 percent failure rate of this method.” The researcher seems to be referring to the roughly 20 percent of women who take Plan B but still become pregnant (in the medical sense of embryo implantation). It does not seem to me that these two sets of statistics are comparable in the way that the researcher suggests. In the study that these scientists conducted, 20 percent of the women ovulated but it is highly unlikely that 100 percent of these women would have become pregnant had they been sexually active during this period. Yet, a comparison between the rate at which Plan B fails to prevent pregnancy and the ovulation rate of the women in the study relies on making this assumption.

Renee Woodward neither confirms nor denies that Plan B prevents the implantation of an embryo (“A woman’s view on Plan B”, Nov. 7). She seems to hold that the evidence about whether or not Plan B prevents implantation is inconclusive at best. This may be the most reasonable conclusion, based on currently available research. Yet, if you will allow me to play the arm-chair pharmacologist for a moment, I will offer a reason for holding that Plan B might act as an abortifacient. Let’s begin with two uncontroversial facts. First, taking Plan B only prevents ovulation in women who have not started the ovulatory phase of their fertile period. Thus, some women taking Plan B could potentially conceive a child. Second, hormonal contraceptives like Plan B alter the inner lining of the uterus in such a way that the uterine wall becomes a less hospitable environment for the implantation of an embryo. Plan B does not make implantation impossible but it does make it more difficult. It is hard to believe that the occasional failure of embryos to implant never has anything to do with the well-known effects of Plan B on the uterine wall. To the extent that taking Plan B plays a role in preventing implantation, a person bears a moral responsibility for acting in such a way that a human person is harmed, indeed, dies – assuming, of course, that a human embryo is a human person.

Andrew Rosato

graduate student


Nov. 7