Unexpected Pregnancy

Pregnancy rates after a vasectomy are estimated to be very low, about 1 in 1,000. There are two main reasons for an unexpected pregnancy:

• Residual sperm were still alive when the partners had unprotected sex. This is the most common reason for an unexpected pregnancy after a vasectomy. Men should make sure they have follow-up sperm analysis testing. They should also continue to use birth control until their doctor notifies them that the test results confirm sterility.
• Failure of the procedure and recanalization. Failure in some cases is due to a technical error, but most often it is due to recanalization -- when the cut ends of the vas spontaneously reconnect. Success rates are best when an experienced surgeon performs the vasectomy.

Residual Live Sperm and Resuming Sexual Activity

Once the patient feels comfortable, he can resume sexual activity, usually in about a week. During ejaculation, the patient may experience some discomfort in the groin and testicles at first due to the contraction of the vas deferens. This almost always diminishes as the tissues heal.

However, after the operation there are always some active sperm left in the semen for several months so the risk for pregnancy persists. It is essential that the patient and his partner continue to use other methods of birth control until his sperm count is zero. The patient is considered sterile only when there are no live or moving (motile) sperm in his semen. It takes, on average, around 3 months or 20 ejaculations to clear the viable sperm from the reproductive system, but it may take some men as long as 6 months to become sterile.

About a third of men experience a recurrence or persistence of sperm that have no ability to move (immotile) 12 weeks after surgery and, in one study, about 7% had persistently immotile sperm. Immotile sperm, however, cannot swim up the vaginal canal and pose no danger for fertility. In rare cases, vasectomies have to be repeated because live sperm persisted in the semen. The risk for sperm surviving indefinitely is, however, very low.

Recanalization

The primary reason for vasectomy failure itself is recanalization-- when the cut ends of the vas deferens spontaneously reconnect. Recanalization in some cases may be due to sperm granulomas. These are tiny balls of debris that form from sperm, scar tissue, and white blood cells at the incision site. Cells lining the inside of the vas deferens grow through the scar tissue and form a new channel through which the sperm can now move. In general, surgeons can reduce the risk for recanalization by leaving a gap between the two cut ends.

This natural vasectomy reversal can occur after any vasectomy surgical procedure, but it is uncommon, with most studies reporting it occurring in less than 1% of cases. When recanalization does occur, sperm counts are almost always very low and pregnancies are still rare. Most cases of recanalization develop within several months after the operation. In very rare cases (about 0.6%), sperm have reappeared a year or even longer after vasectomy.