So the system might not be full proof but it is one hell of a lot better than the current system.
And how does a women not know their pregnant when they don't have a period for 6 months ?
Maybe we could ban birth control methods that increase the time between periods as they remove the most effective way to tell if you are pregnant or not.
Unless I missed something and some women actually do continue to have their period while pregnant though it is something I have never ever heard about.