Maybe this says something not so great about me, but I love stories like this:

It is believed that the method works because it prevents conception from occurring. But ... it may owe much of its success to the fact that embryos conceived on the fringes of the fertile period are less viable than those conceived towards the middle.

We don’t know how much lower embryo viability is outside this fertile period ... but we can calculate that two to three embryos will have died every time the rhythm method results in a pregnancy.

Apparently the rhythm method kills far more embryos than any other form of contraception.

Just don't tell the Catholic church; they might decide (again) that even the rhythm method is immoral.