Cleopatra kept herself unpregnant by sneezing after having sex. Same thing here only opposite. Those little swimmers stay alive for what, 36 hours?
36 hours is one thing I'd heard, 72 hours another.
*shrugs*
Dunno, they can extract DNA evidence from it even 50 years after the fact if a 'sample' were preserved in one fashion or another.
That was the only info that had been of interest to me.