A couple is advised to use barrier methods after vasectomy till:

Ans. is b, i.e. No sperms in ejaculateRef: Textbook of Gynae sheila balakrishnan 1st/ed, p373, Dutta Obs 7th/ed, p553Sterility does not occur immediately after vasectomy.Sperms remain in the semen for 15-20 ejaculation, requiring continued contraception for about 3 months. So the couple is advised to use some form of contraception for the next 3 months or 15-20 ejaculates, but this can vary from person to person. So the best thing to do is to repeat the semen analysis and confirm that the male partner has become azoospermic.This is the reason why after vasectomy, 2 separate semen analysis should be done to confirm the absence of sperms in the ejaculate and then additional contraception discontinued.