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May 25, 2006

The fertile fringe: Rhythm method criticised as a killer of embryos

This just in from reader John:

Philosopher Luc Bovens argues that the rhythm method is wrong because it increases a couple's chances of creating embryos that don't become pregnancies:

The range of birth control choices may have become narrower for couples that believe the sanctity of life begins when sperm meets egg. The rhythm method, a philosopher claims, may compromise millions of embryos.

“Even a policy of practising condom usage and having an abortion in case of failure would cause less embryonic deaths than the rhythm method,” writes Luc Bovens, of the London School of Economics, in the Journal of Medical Ethics.

With other methods of contraception banned by the Catholic church, the rhythm method has been one of the few options available to millions.

In using the rhythm method, couples avoid pregnancy by refraining from sex during a woman’s fertile period. Perfect adherents claim it is over 90% effective – i.e. one couple in 10 will conceive in an average year. But, typically speaking, effectiveness is estimated at closer to 75%.

Now Bovens suggests that for those concerned about embryo loss, the rhythm method may be a bad idea. He argues that, because couples are having sex on the fringes of the fertile period, they are more likely to conceive embryos that are incapable of surviving. [...] [New Scientist]

I think Bovens has produced a near-reductio ad abdurdum for the claim that moral status starts at fertilization. (Update 2, based on the original paper, I suspect that Bovens meant to do exactly that, especially given his wry concluding paragraph: "And finally, one person’s modus ponens is another person’s modus tollens. One could simply conceive of this whole argument as a reductio ad absurdum of the cornerstone of the argument of the pro-life movement, namely that deaths of early embryos are a matter of grave concern.")

Update 1: Commenter Tofumar asked why Bovens' argument is a near reductio of the fertilization=person theory. Here's my argument, formulated on the basis on the New Scientist article, which, having read the paper, I now suspect of being a little off-base.

The so-called rhythm method exploits the fact that women are only capable of conceiving for a few days out of every month. The Catholic Church says it's okay for married couples to try to avoid pregnancy by guessing which days those are and abstaining on those days. Bovens' worry couples who only have sex on presumed non-fertile days may inadvertently end up fertilizing gametes that have been sitting around for way too long. Embryos are conceived on this "fertile fringe" are more likely to be non-viable than those conceived during the monthly sweet spot. So, Bovens suggests, the consistent use of the rhythm method may create far more doomed embryos than necessary. If you believe that a fertilized ovum is a full-fledged person, like your next-door neighbor, you can see how it might be morally problematic to follow a metric that might doom several extra "neighbors" every year, year in and year out, for the next couple decades....

It seems a little odd to classify intrinsically non-viable embryos as a rights-bearing subjects. Ex hypothesi, these embryos aren't even potential fetuses or potential babies because they're too damaged to gestate.

On the other hand, if you assume that embryos are persons, it makes sense to say that you have a responsibility not to kill them. However, Bovens is entertaining a much more radical claim, namely that you have an affirmative duty not to create dead-end embryos in the first place because they are going to die.

Bovens is arguing that the rhythm method is wrong because it's more likely to create doomed embryos. But what's the alternative? Presumably, just to have sex whenever you want. But couples who refuse to plan their reproduction are recklessly risking the production of doomed embryos.

Maybe the answer is not to abandon the rhythm method, as Bovens suggests, but rather to adopt a more conservative rhythm. Classifying more days as "unsafe" reduces the likelihood of doomed embryos. However, the rhythm method probably doesn't work any better for avoiding the edges of fertility than it does for avoiding fertility. A couple who tries to practice a modified rhythm method is still more likely to create doomed embryos than a couple who uses more effective forms of birth control.

If doomed embryos have human rights, it seems unconscionable not to use the most effective methods of artificial contraception during potentially potentially fringe-fertile times. So, Bovens' position seems to imply that couples must use artificial contraception, but only when they think they can't get pregnant.

Of course, stale gametes aren't the only cause of doomed embryos. Many embryos made from perfectly fresh gametes can't gestate because of chromosomal defects or other flaws. I've read that a significant percentage of all fertilized ova die before implantation. So, if you take the fertilization=personhood claim seriously, then trying to conceive is also morally problematic because you risk killing a lot of embryos before you make one that sticks.


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Perfect adherents claim it is over 90% effective – i.e. one couple in 10 will conceive in an average year. But, typically speaking, effectiveness is estimated at closer to 75%.

I know this is sort of outside the main gist of the post, but can we focus on it for just a second? Saying that 1-in-10 get pregnant this year equals a 90% effective rate is horrible, horrible math.

90% effective would be that 1-in-10 adherents becomes pregnant during whatever window the couple is practicing it, not "one year." If it's one in ten every year who become pregnant, the two-year effective rate drops to somewhere in the 80s (my head is too fuzzy right now to actually figure it out) and the three-year rate even further.

I'm not sure whether it's the article or the adherents who got it wrong, but someone is badly screwing up the numbers. Given the fervor around pregnancy and contraception, it's a pretty important issue to get correct. If it's 90 percent effective, that's not bad. if it's 90 percent per year effective, that's an extraordinary argument in favor of artificial contraception.

If the problem is sex on the fringes of the fertile period, couldn't that just be solved with a sparser rhythm?

Isn't the point that we can't take this seriously?

The typical effectiveness rate is expressed per year, jhupp, so "90% effective" means "90% effective per year."

I like Bovens' move here. But a quick question for Lindsay: How exactly is this a (near) reductio of the claim that moral status begins with the union of sperm and egg? I fear I may be a bit slow on this one, but I can't quite see how the argument would run.

It's because the Catholic church's official position is that the rhythm method is an acceptable form of birth control, but all others are not because they're unnatural or because they kill embryos or whatever.

I think you're right, Thomas. However, that makes the Catholic Church's doctrine even more contradictory. Sex is only for married people who are open to the possibility of conception. However, the value of human life is supposed to trump everything in Catholic theology. So, being a married couple who is open to the possibility of conception is necessary, but not sufficient for theologically-correct sex.

If embryos are people, and creating a doomed embryo is a form of abortion/murder/unjust killing, then it seems that even married couples aren't entitled to have sex if there's any chance of it killing innocent person.

Bovens' worry is "stale" gametes may fuse after they're too old to create a viable embryo.

My first question is why we should define a intrinsically non-viable embryo as a rights-bearing subject. After all, it's not even a potential person because it's too defective to undergo gestation.

It's one thing to say that you have a duty not to kill a developing embryo (if you think it's a person), but it's quite another to say that you have a duty to refrain from creating an embryo with a very short natural lifespan.

Bovens is arguing that the rhythm method is wrong because it's more likely to create doomed embryos. But what's the alternative? Presumably to just have sex whenever you feel like it. But if you did that, you'd probably end up creating a lot of doomed embryos anyway.

Besides, the edges of fertility aren't the only time that embryos fail to implant. There are other factors that can also doom an embryo. Bovens isn't seriously suggesting that, say, older couples shouldn't even try to concieve because there's a high risk that they will kill a lot of embryos before they get one to implant?

If there's a moral principle here, it's the duty to avoid creating any doomed embryos. That ought to be an argument for contraception. The rhythm method is unreliable precisely because we can't tell exactly when the edges of fertility are.

But I assume that Bovens is against artificial contraception as well as "natural" family planning. Hence the quasi-reductio.

He can't really be serious about the moral status of the fertilized ovum because it leads to absurd conclusions regarding the ethics of unprotected sex between people who are trying to conceive or who are perfectly willing to carry a pregnancy to term.

Ditto Alon Levy. Customarily, effectiveness of contraception is expressed as a given percentage on an annual basis. So yes, a 10% failure rate per year is quite high if you are planning to use it for any length of time.

Re the larger point of the post: I am glad that I am not the only one who sees the ridiculousness of the "seamless garment" in this light. By defining where "life begins" by resort to the lowest common scientific denominator of separate human material (i.e., single cells with separate DNA imprint), anti-choice mongers virtually cede that traditional religion has nothing to tell us about the nature of personhood. I can only wonder at how slavishly the Church is willing to follow science on this issue.

Lindsay, I'm no theologian, but isn't the embryo only a component of the Catholic position? Don't they rely on the "theology of the body" doctrine that sex should be exclusively reserved for a married couple having intercourse "open to the possibility of conception?" In other words, don't they have a basis for the rule that is independent of the action of any gamete?

>the Catholic position


Being that you're a philosopher and pro-choice advocate I thought you'd like this story, Lindsay. That has to be one of the most absurd anti-contraception arguments I've read in a long, LONG time.

Oh for the love of God. If these anti-abortion crackpots would just spend a fraction of the energy they waste on wringing their hands over stupid embryos in doing something constructive, the world might be a better place. Is a fetus sentient? No. Is there a shortage of babies? No. Abortion is the “save-the-whales” issue for the right. They can work up righteous outrage over helpless “beings” brutally snuffed out by cynical thugs, which can be used to get out the vote and the contributions.

Dancing around on the head of the “Does Life Begin at Conception?” pin doesn’t provide any real benefit to real babies born in the real world. If “stale” gametes come to term as damaged or disabled children, then there might be something to this. If not, then this is just another typical example of theological tail-chasing.

I thought the rhythm method was for reducing sex, not pregnancy.

By introducing the fringe times in this, he's confused the issue. Odds are about half of fertilized eggs die. That means unless you use a contraceptive method that prevents conceiving altogether, like the pill, you are a baby murdering monster. Especially if you're always trying to get pregnant.


One person's reductio is another's modus ponens. If all sex must be open to procreation, and sex that is open to procreation is ethically impermissible because it violates the Catholic principle of the sanctity of life, then clearly all sex is unethical. The sanctity of fertilized eggs doesn't justify artificial contraception, it simply entails that we all have a moral duty to be celibate.

The Shakers had the right idea, and with any luck Bovens' argument will convince the die-hard Catholics to follow in their footsteps.

What about the just barely viable? Is there any evidence that there are higher rates of birth defects for couples using the rhythm method? That would be a real substantive moral reason to not use the rhythm method at least if you were unwilling to abort.

From "Our Phantom Children", by Jared Diamond, Natural History, May 1992.

"Of pregnancies clearly recognized by the mother, only 15 percent end in miscarriage. However, modern hormonal tests can detect many other pregnancies that terminate within a couple of weeks, indicating a total miscarriage rate of about 50 percent rather than 15 percent. [...] Outcomes of attempted artificial fertilizations of ova within the fallopian tubes suggest that still more embryos are lost even before implantation, adding up to a total loss rate as high as 80 percent."

Well, after reading Bovens’ paper I see it really is a joke. Though just the effort of thinking about people pointlessly thinking about life beginning at conception or not is wearisome. Whenever I hear about that crap I can’t help but recall Swift’s Lilliput vs. Blefuscu's useless egg eating dispute.
Maybe as a fish biologist I’m biased. Every autumn here in the Northwest one can see salmon eggs not safely buried in stream bed gravel, rolling around loose by the millions, being scooped up by other fish, gulls, mink, dippers, or mostly just rotting. Some eggs are fertilized, others not, all once potentially an adult salmon but none so now, and none now worth a second thought.

Actually, according to friends of mine who use it, the rhythm method does work at least as well as any other means of avoiding pregnancy in a hetero relationship, but with two major requirements:

One, the woman has to become intimately acquainted with how her body works. Not just a matter of counting days since her last period ended: she has to know when she ovulates.

Two, the woman has to become the only decisionmaker about when the couple have penetrative sex. Both the man and the woman have to accept without question that the woman is the one who knows when her fertile days are, and is the only one who gets to decide when they have hetero intercourse.

Neither requirement is something the Catholic church could openly support. Or, most likely, support at all. Yet both are required for the "rhythm method" to work.

Re: Jesurgislac. Like W., the woman has to say "I'm the decider".

The biggest problem is that the whole thing requires white people to have rhythm.

What I think is required is the reverse rhythm method. If the concern is about the loss of blastocysts of whatever viability, then the only acceptable choice is penetrative intercourse restricted to fertile times, as determined by the woman who knows her body, and that the couple be in a state willing to carry the results to term.

I like SteveG's observation, too.

cfrost, I agree that Bovens is playing a wry philosophical joke on the prolife movement. I added an update to the original post last night after I read his paper.

So Mr. Bovens was funnin' with the pro-lifers? Well, he sure had us all going there for a little while. Very clever. Too clever, really. You philosophers need to be a little more obvious with your humor. Maybe he should have put a smiley wink ;-) after he first stated his argument, or maybe ended his article by saying "Now pull my finger." That would keep with philosophical writing standards and practices, wouldn't it?

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