Chances of Pregnancy after Vasectomy

Patient: I had a vasectomy 10 years ago, it was unsuccessful, so I had the second vasectomy now I find out my girlfriend is pregnant, is this really possible?

Doctor: It is possible! It may take as long as 12 weeks before sterility can be confirmed following vasectomy. Therefore any unp rotected sexual intercourse during this 12 week window may result in pregnancy.