"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."
I have read other sources on this argument before, and have related it to others in my many writings and arguments against all forms of contraception. I have long criticized the Roman Catholic approval of NFP (natural family planning) as hypocritical on a theological level, regardless of any abortifacient arguments. In addition, I believe the scientific assumptions made in this research article are quite plausible, given the moderate knowledge of human reproductive physiology I have. The paper was published in the Journal of Medical Ethics (one of the British Medical Journal's publications).
As with the "unproven" assumptions we have showing hormonal birth control (the Pill, etc.) to have an abortifacient component, why would anyone knowingly employ a method of family planning which may lead to increased risks of death for the unborn?
Of course most of you know that according to my position this is a moot point. Regardless of the abortifacient nature of all the favored methods of family planning, ALL FAMILY PLANNING is against God's Word. My position does, however, allow for the potential application of ethical principles (casuistry) according to the Lutheran ethic of "conflicting absolutes," which leads us to choose the lesser evil and throw ourselves on the mercy of Christ.
UPDATE: In response to his critics, the author of the article in the Journal of Medical Ethics has posted a reply on the British Medical Journal website. The reply gives further official documentation to his argument and does a good job of answering the most common objections voiced to his original article.