It is essential that the couple must use other forms of contraception following the vasectomy operation until the man has had two samples of semen examined to make sure that there are no sperm present. It is advised to have a minimum of 20 ejaculations before sending these samples to the laboratory at 16 and 18 weeks after the operation.

In a small number of cases these will not be fully clear and the tests will have to be repeated. Very occasionally the semen may be very slow to clear and sperm can be present more than a year after the operation.