It is important for the patient to realize that the vasectomy does not produce instant sterilization. A substantial amount of sperm still remain in the vas deferens beyond the portion that was removed. In most men, it takes from 10 to 14 ejaculations over the next 2 months or so before a sperm count of zero is reached. The patient typically is asked to produce a semen sample for analysis at about 3 months after surgery. Until then, another form of reliable birth control should be practiced.

In rare cases, patients continue to show sperm in their samples for up to a year after surgery. This may be the result of poor sperm migration out of the vas deferens after surgery, or it may indicate that the severed ends of the vas deferens have reattached themselves to one another, a condition called recanalization. The only solution to this problem is a repeat vasectomy.

The incidence of vasectomy failure is estimated between .5% and 1% and varies with the skill and experience of the physician and with the approach used to block the tubes. It is for this reason that testing semen samples is essential. If, in the unlikely event that repeated semen checks show persistent live moving sperm, your vasectomy will have to be repeated.