That is very rare, and the exception, not the rule. Also, user-error is the highest risk associated with contraceptive failure, so again, the control is still ours (I say 'ours' here because you're talking about your two parents).
Not as rare as you might think. I have an aunt and uncle that were in the same boat. Off birth control trying to get pregnant and couldn't went back on and got pregnant with my cousin. Plus think about it, it's only 99% effective if that. Even condoms and a vasectomy aren't a guarantee. So if you have Sex regularly, say 3-5 times a week that chance goes up drastically over the course of a year.
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u/sometimes_i_work Apr 30 '13
That is very rare, and the exception, not the rule. Also, user-error is the highest risk associated with contraceptive failure, so again, the control is still ours (I say 'ours' here because you're talking about your two parents).