A pejorative term used to refer to an outmoded form of natural contraception
known as the Rhythm Method
. Often used mistakenly to refer to coitus interruptus (the 'pull-out method'). The Rhythm Method officially fell out of favor with "The Vatican" in the early 1980's with advances in the study of the female reproductive cycle.
Current methods of Natural Family Planning (non-chemical and non-barrier contraception), when used correctly and consistently, have been shown in several peer-reviewed studies to be over 99% effective. This is similar to the efficacy of 'the pill.'
It should be noted that the use of such a term often indicates it's user has a bigoted and intolerant attitude against people who practice a religion they do not agree with.
By following the Creighton method or the Billings Ovulation method, faithful Catholics no longer have to play so-called "Vatican Roulette"
They have six kids? They must be playing Vatican Roulette.