The August issue of Harper's features an excerpt from "The Rhythm Method and Embryonic Death," by Luc Bovens, published in the June issue of the Journal of Medical Ethics. In this paper, Professor Bovens argues that the rhythm method of birth control--the only method approved by the Catholic church--may be responsible for "massive embryonic death."
Couples who use the rhythm method try to avoid pregnancy by having sex during the time in which conception is the least likely to occur and during which there is lower ovum viability. As a consequence, they avoid pregnancy by avoiding conception, but they also because conceived ova have such a small chance of surviving. Says Bovens:
Nonetheless, one could argue that even if the 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. Even a policy of practicing condom usage and having an abortion in case of failure would cause fewer embryonic deaths than the rhythm method.