Rhythm method kills more embryos than condom use

Luc Bovens, from the London School of Economics, looked at the biology of the rhythm method. The rhythm method is the only form of birth control allowed by the Roman Catholic church. Couples using it avoid sex during the woman's fertile period. But Bovens says it leads to more embryo deaths than other contraceptive methods. Most eggs that are fertilized die anyway. But "stale" eggs outside the fertile period are even more likely to die.

Bovens estimates that if the rhythm method is 90% (per year) effective, and if conceptions outside the fertile period are about twice as likely to fail as to survive, then around the world "millions of rhythm method cycles per year depend for their success on massive embryonic death."

"If you're concerned about embryonic death, you've got to be consistent here and give up the rhythm method," Bovens says. "Even using condoms and having an abortion in case of failure would cause fewer embryonic deaths than the rhythm method," he writes in the Journal of Medical Ethics (Volume 32, page 355).

Roger Gosden at the Center for Reproductive Medicine and Infertility in New York says the suggestion is reasonable.