Coitus Interceptus

Science, technology, and life.
Jan. 5 2009 10:15 AM

Coitus Interceptus

I'm just back from vacation and trying to catch up on the war in Gaza. More on that later. But first, something I didn't have a chance to get to before the break: the Vatican's latest pronouncement on fertility technology. Apparently the men in Rome are having trouble understanding some nuances of the female reproductive system.

The pronouncement comes in the form of Dignitas Personae , an instruction from the Congregation for the Doctrine of the Faith, which articulates official Catholic positions. This document covers several interesting topics, which I hope to get to in the days ahead. But the one that calls for rebuttal right away is the section on "[n]ew forms of interception and contragestation." It says:

William Saletan William Saletan

Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

Alongside methods of preventing pregnancy which are, properly speaking, contraceptive, that is, which prevent conception following from a sexual act, there are other technical means which act after fertilization, when the embryo is already constituted, either before or after implantation in the uterine wall. Such methods are interceptive if they interfere with the embryo before implantation and contragestative if they cause the elimination of the embryo once implanted.


This is an astute and useful set of distinctions. Unfortunately, the CDF immediately proceeds to violate them. Here's its next paragraph:

In order to promote wider use of interceptive methods [a footnote here specifies " morning-after pills "], it is sometimes stated that the way in which they function is not sufficiently understood. It is true that there is not always complete knowledge of the way that different pharmaceuticals operate, but scientific studies indicate that the effect of inhibiting implantation is certainly present, even if this does not mean that such interceptives cause an abortion every time they are used. ...

Really? Is the effect of inhibiting implantation "certainly present"? Let's review the mechanics of morning-after pills, specifically levonorgestrel, marketed as Plan B. The problem with the CDF's statement is that this "interceptive" is chemically identical to the best-known contraceptive: the pill. And the risk that this drug

will prevent implantation of an embryo is purely theoretical. There is no documented case of such a tragedy, since we have no way to verify conception inside a woman's body prior to implantation without causing the embryo's death. Even theoretically, the risk is vanishingly small , since the primary effect of oral contraception is to prevent ovulation , and the secondary effect is to prevent fertilization . To classify oral contraception as abortifacient, one would have to posit a scenario in which the drug fails to block ovulation, then fails to block fertilization, and yet somehow, having proved impotent at every other task, manages to prevent implantation.

So, the assertion of an anti-implantation effect is theoretically unsound. But what do the data show? Two years ago, the world's leading expert on levonorgestrel, James Trussell, co-authored an analysis of the available research in the Journal of the American Medical Association . The analysis confirmed that that anti-ovulation effects wipe out any data suggesting a possible anti-implantation effect. It concluded:

Published evidence clearly indicates that Plan B can interfere with sperm migration by altering the cervical and uterine environment, and that preovulatory use of Plan B usually suppresses the LH surge either completely or partially, which in turn either prevents ovulation or leads to the release of ova that are resistant to fertilization. Epidemiological evidence rules strongly against interruption of fallopian tube function by Plan B. Evidence that would support direct involvement of endometrial damage or luteal dysfunction in Plan B's contraceptive mechanism is either weak or lacking altogether. Both epidemiologic and clinical studies of Plan B's efficacy in relation to the timing of ovulation are inconsistent with the hypothesis that Plan B acts to prevent implantation.

In fact:

Progestational drugs, including levonorgestrel, are used therapeutically in assisted reproduction because they increase the rate of successful implantation and pregnancy . That observation a prior reduces the likelihood that Plan B interferes with implantation; it even raises the counterintuitive but undocumented possibility that Plan B used after ovulation might actually prevent the loss of at least some of the 40% of fertilized ova that ordinarily fail spontaneously to implant or to survive after implantation.

So, in summary:

[T]he ability of Plan B to interfere with implantation remains speculative, since virtually no evidence supports that mechanism and some evidence contradicts it. ... [T]he best available evidence indicates that Plan B's ability to prevent pregnancy can be fully accounted for by mechanisms that do not involve interference with postfertilization events.

So much for the question of effect. But what about the other part of the moral equation: intent? The Vatican document, still referring to morning-after pills, says that "anyone who seeks to prevent the implantation of an embryo which may possibly have been conceived and who therefore either requests or prescribes such a pharmaceutical, generally intends abortion."

But a woman who requests a morning-after pill doesn't necessarily seek to prevent an embryo's implantation. In fact, as we just showed, it would be irrational of her to seek that effect, since no evidence supports it. In fact, given the evidence, it would make just as much sense for her to request the pill in order to prevent embryonic loss. And anyone who has ever taken a morning-after pill knows that at that moment, your actual intent is to avert pregnancy at the earliest possible stage of the process, which happens to be ovulation.

Bottom line: The perceptive analytical framework established by Dignitas Personae , combined with the best scientific evidence and analysis, clearly implies that morning-after pills are contraceptives, not interceptives. Therefore, from the standpoint of respecting embryonic life, you may take them in good conscience.



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