[Errors in my arguments were fixed and additional material was added after initial publication. – Funky]
St. Blog’s Parish will soon be all aflutter with news that Luc Bovens, a professor of philosophy at the London School of Economics, has written an article ("The rhythm method and embryonic death", J Med Ethics 32: 355-356) that links the use of the "rhythm method" with embryonic death, i.e. early miscarriage or spontaneous abortion. (Fedora Tip: UnSpace)
"Some proponents of the pro-life movement argue against morning after pills, IUDs, and contraceptive pills on grounds of a concern for causing embryonic death. What has gone unnoticed, however, is that the pro-life line of argumentation can be extended to the rhythm method of contraception as well. Given certain plausible empirical assumptions, the rhythm method may well be responsible for a much higher number of embryonic deaths than some other contraceptive techniques."
Though some responses to the sloppy arguments made in this paper have been made by American Papist, Epiphany, and other bloggers, I do not believe the responses I’ve so far seen address the scientific/statistical aspects of Bovens’ claims. For instance, they rightly point out that the rhythm method was long ago replaced by much more reliable empirical methods collectively known as natural family planning (NFP). However, I suspect that Bovens chose to deliberately seem ignorant of pro-life/anti-contraceptive terminology in order to subtly mock what he sees as ignorance of reproductive medicine on the part of those who call the birth control pill abortifacient. I fear that Catholic bloggers have allowed themselves to be distracted by a red herring.
Let’s see what kinds of claims Bovens makes and how reasonable they are. We’ll start with his assumptions.
"The first assumption is that there are a great number of conceptions that never result in missed menses. There are estimates that only 50% of conceptions actually lead to pregnancies."
This is in agreement with the MedlinePlus’ Medical Enyclopedia. However, a letter by Dr. Mark Whitty, MSc to the Journal of Medical Ethics in response to Bovens article stated the following.
"Boven’s first assumption that 50% of natural human conceptions are lost is an often-repeated figure based on problematic research in 1956 (1) using histological anaysis of hysterectomies where intercourse was encouraged prior to surgery. The higher figure of 78% often quoted rests on a 1975 analysis (2) of an hypothesis based on a series of weak assumptions. Animal studies commonly give percentages in single figures."
Based on abortifacient device and drug failure rates discussed later, natural birth control methods may be on far more equal footing with the Pill than Bovens assumes.
"The second assumption is that, even in clinical trials, the rhythm method can fail due to the fact that a pregnancy results from sexual intercourse on the last days before and the first days after the prescribed abstinence period."
Every birth control method has a non-zero failure rate, and when NFP fails, that failure is due to sexual intercourse at the fringes of a woman’s fertile period. That is, if a mistake is going to be made – a real mistake, not a whim to "take a chance" – it is going to happen when intercourse is had a day later or a day earlier than it ought to have in order to avoid conception.
"Estimates of the effectiveness of the rhythm method vary in the literature, but let us set its effectiveness for clinical trials at 90%—that is, conscientious rhythm method users can expect one pregnancy in ten woman years."
FDA data do not seem to differentiate between NFP and other forms of periodic abstinence, but data I’ve seen indicate that with typical use NFP has a 3 to 10% failure rate, so Bovens’ estimate of 10% is reasonable.
"The third assumption is that there is a greater chance that a conception will lead to a viable embryo if it occurs in the centre interval of the fertile period than if it occurs on the tail ends of the fertile period. This assumption is not backed up by empirical evidence, but does have a certain plausibility. From assumption one, we know that there is a high embryonic death rate. It seems reasonable to assume that an embryo that results from an ‘old’’ ovum (that is waiting at the end of the fertile period) or an ‘old’ sperm (that is still lingering on from before ovulation), and that is trying to implant in a uterine wall that is not at its peak of receptivity, is less viable than an embryo that comes about in the centre interval of the fertile period. Let us make a conservative guess that the chance that an embryo conceived in the centre interval of the fertile period, which coincides with the abstinence period in the rhythm method—let us call this ‘the heightened fertility (HF) period’—is twice as likely to be viable as an embryoconceived at the tail ends of the fertile period."
"So now let us run the argument. We know that even conscientious rhythm method users get pregnant. Conception may occur due to intercourse during the tail ends of the fertile period and the conceived ovum may turn out to be viable. Rhythm method users try to avoid pregnancy by aiming at the period in which conception is less likely to occur and in which viability is lower. So their success rate is due not only to the fact that they manage to avoid conception, but also to the fact that conceived ova have reduced survival chances. Just like in the earlier case of pill usage, we do not know in what percentage of cases the success of the rhythm method is due to the strictly contraceptive workings of the technique and in what percentage of cases it is due to the reduced survival chances for the conceived ovum. None the less, along with [Randy] Alcorn, one could argue that even if the latter mechanism has only limited effectiveness, it remains the case that millions of rhythm method cycles per year globally depend for their success on massive embryonic death."
Before I procede to poke holes in Bovens’ arguments, let’s assume that Bovens is right about HF and non-HF (fringe) conceptions having different embryo survival rates. In that case, he would be right that NFP practitioners might be responsible, albeit unintentionally,for a large number of spontaneous abortions. There is an easy solution to the problem, though. Simply modify the rules of NFP. For those couples trying to avoid conception (TTA), the rules of NFP should be adjusted to be stricter around the fertile period. For those trying to conceive (TTC), the rules need to adjusted so that intercourse is timed to be closer to ovulation.
Therein lies the beauty of NFP in comparison to the old rhythm method. It’s not based on a mythical 28-day cycle or some mean number of fertile days per cycle. It’s based on observable signs such as basal body temperature and quality of cervical fluid. A woman need not have regular cycles at all and still know when she’s fertile. Those who would like more detailed information are encouraged read Taking Charge of Your Fertility by Toni Weschler, a pro-contraception, pro-choice woman with no theological axe to grind. Returning to Bovens:
"Let us try to make the argument more vivid. Pro-lifers oppose IUDs because their main mode of operation is to make embryonic death likely. Now suppose that we were to learnthat the success of the rhythm method is actually due, not to the fact that conception does not happen—sperm and ova are much more long lived than we previously thought—but rather because the viability of conceived ova outside the HF period is minimal due to the limited resilience of the embryo and the limited receptivity of the uterine wall. If this were the case, then one should oppose the rhythm method for the same reasons as one opposes IUDs. If it is callous to use a technique that makes embryonic death likely by making the uterine wall inhospitable to implantation, then clearly it is callous to use a technique that makes embryonic death likely by organising one’s sex life so that conceived ova lack resilience and will face a uterine wall that is inhospitable to implantation. Furthermore, if one is opposed to IUDs because their main mode of operation is to secure embryonic death, then, on the assumption that one of the modes of operation of the pill is to make embryonic death likely, one should be equally opposed to pill usage. This is essentially Alcorn’s argument and assuming that the empirical details hold, consistency does indeed drive IUD opponents in this direction. If, however, our empirical assumptions about the rhythm method hold, then one of its modes of operation is also that it makes embryonic death likely. And if embryos are unborn children, is it not callous indeed to organise one’s sex life on the basis of a technique whose success is partly dependent on the fact that unborn children will starve because they are brought to life in a hostile environment?"
Indeed that would be callous, if Bovens empirical assumptions about periodic abstinence hold. Let’s see whether or not they do.