How do we know if the vasectomy was successful?

After the procedure, your vasectomy will not be effective immediately. It is important that you use an alternative method of contraception until your semen has been confirmed to be free of sperm.
You will need to perform a semen analysis 3-4 months after the vasectomy. The semen specimen will be checked under a microscope to see whether there are any sperm left.
If there are no sperm cells seen, the vasectomy is considered to have been successful.
This post-vasectomy semenalysis (PVSA) carries an additional out-of-pocket expense, payable to the pathology laboratory who process the sample.