Folks who want to get that extra basket of fruit or cheese for the holidays should pass along Prof. Luc Bovens's essay "The Rhythm Method and Embryonic Death" to their local Roman Catholic bishop--and a carbon copy to his cardiologist. The cardiologist will be grateful for the business. In the June _Journal of Medical Ethics_ Prof. Bovens, a philosopher at the London School of Economics, points out a flaw in the Catholic Church's support of the rhythm method: embryos conceived notwithstanding recourse to the rhythm method may be at greater risk. See below.
In "The Rhythm Method and Embryonic Death" (http://jme.bmjjournals.com/cgi/content/full/32/6/355?maxtoshow=&HITS=10&hits=10&RESULTF
ORMAT=&author1=bovens&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=re
levance&resourcetype=HWCIT) Luc Bovens argues that the Roman Catholic Church's suppport of the rhythm method is at odds with its tenet "that deaths of early embryos are a matter of grave concern."
According to Bovens, "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...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."
Moreover, fewer embryos would die if condom use were permitted together with abortion when the method failed.