Vasectomy is tremendously effective as a form of permanent birth control but vasectomy is not always 100%. Pregnancy after vasectomy is possible but extremely unlikely.

The overall chance of a pregnancy after vasectomy is about 3 out of 1000 procedures or 0.3%.

What does vasectomy failure mean?

Experts in vasectomy debate what constitutes vasectomy failure. Is vasectomy failure any sperm in the ejaculate after a procedure or is it pregnancy? Obviously any pregnancy caused by a man after vasectomy is a vasectomy failure.

A more difficult question is how much sperm is allowable in the ejaculate after vasectomy? Although most men will have no detectable sperm in their ejaculate, some men will have small amounts of sperm in their ejaculate after a vasectomy procedure. Many of these men will technically have a vasectomy failure but will never father a pregnancy. Many people are not aware that large numbers of sperm are required to cause pregnancy. A man can have motile sperm counts as high as 20 million per milliliter and may never father a child.

Reasons for vasectomy failure

Most patients will define vasectomy failure as any pregnancy that occurs after a vasectomy procedure.

There are four reasons why pregnancies occur after vasectomy:

1. Failure to use back up method within the first three (3) months of vasectomy
2. Missed vas deferens
3. Reconnection of the vas deferens
4. Spousal infidelity

Most common reason: Failure to use back-up method

The most common reason for pregnancy after vasectomy is failure to use a back-up method of birth control within the first three (3) months of having a vasectomy. Even though the vas deferentia have been interrupted, viable sperm are present within the upper portion of each vas deferens and inside the seminal vesicles. Pregnancy is always possible until these sperm are released.

It is important to use a good method of back up until a post vasectomy semen sample confirms the absence of sperm.

Missed vas deferens during vasectomy

If the vasectomy is challenging due to patient anatomy (obesity, scar tissue in the spermatic cord, cryptorchidism, extremely thin vas deferens, etc) then the vas deferens could be missed. Alternatively if a difficult vas deferens is not appropriately divided or occluded then sperm can be persistent in the ejaculate after a vasectomy.

Often a skilled vasectomist will have some inclination this is possible during the vasectomy procedure and the post vasectomy semen sample will confirm if the procedure was successful.

It is important to have the follow-up semen analysis three (3) months after your vasectomy procedure.

Reconnection of the vas deferens

Despite an initially successful vasectomy procedure, the divided ends of the vas deferens can reconnect. Most often this occurs in the first three (3) months of the vasectomy procedure. This connection may result in failure to achieve sterility and even pregnancy but equally as likely the patient may never cause a pregnancy.

How do vas deferens reconnect?
After a vasectomy procedure the body deposits healing tissue between the divided ends of the vas deferens. This healing tissue is normal after any procedure and is referred to as granulation tissue.

Since sperm is continually being produced by the epididymis after the vasectomy, pressure from the spermatic fluid in the lower end can create small drainage channels within the intervening granulation tissue. These channels can connect to the upper divided vas deferens and sperm will then have reestablished a direct pathway to the seminal vesicles.

Helpful analogy: Granulation tissue is similar to dumping a large load of sand in the middle of a small creek. The sand may be deposited in such a large amount that the creek water is effectively stopped. Alternatively the flow of water within the creek could make small paths through the sand and the flow of the creek will continue. This flow may re-establish itself at a normal rate or be greatly diminished.

These microchannels may allow sperm to find the upper end and travel to the seminal vesicles. These sperm may be normal in shape and motility or may be abnormally shaped and poorly motile. They may be present in extremely small amounts or large amounts. If present in large amounts and normal shape pregnancy will often occur sooner rather than later and if present in smaller amounts and of abnormal shape pregnancy may never occur or could occur at a delayed time from the vasectomy.

If a couple has frequent sexual intercourse then the sperm may never collect in large enough amounts to cause pregnancy but if sexual intercourse is infrequent the sperm have time to accumulate in larger amounts and eventually cause pregnancy. Another variable to consider is if sexual intercourse occurs during ovulation.

With so many variables is easier to understand why some vasectomy failures will occur ten (10) years or greater after vasectomy.

When one understands the mechanism of vasectomy failure then one can more easily understand the debate behind what constitutes a vasectomy failure. The American Urologic Academy defines a vasectomy as successful if less than 100,000 non-motile sperm per milliliter at present six (6) months or more after vasectomy.

Often the post vasectomy semen sample testing will detect many of the early failures but miss sperm in small amounts that could result in later pregnancy. Even when a late failure occurs very often a repeat semen analysis will not demonstrate any sperm.

The three (3) month follow-up semen sample testing is helpful to detect early vasectomy failures. Late vasectomy failures are uncommon and are often not detected by second semen analysis.

Spousal infidelity

Spousal infidelity can be an equally common reason for pregnancy after vasectomy. This can be a delicate subject to discuss and deal with for couples. It is even more difficult because many vasectomy failures will not have easily detectable sperm during detailed analysis. Often a DNA test on the baby will have to be performed to prove paternity if there is any doubt.

A negative semen sample will not prove or disprove paternity in the case of pregnancy after vasectomy. There are many cases of a man genetically being proven the father and sperm are not detectable on several semen analysis.

Often a serious discussion between the couple will be required to determine if pregnancy is the result of spousal infidelity. Often there are other warning signs in the relationship that could indicate infidelity. Ultimately a DNA test will have to be performed to prove paternity even if the semen sample does not demonstrate sperm.

Late vasectomy failure will occur in approximately 0.3% of all procedures. Statistics on marriage infidelity and divorce in the United States are unreliable but most would agree the chance of infidelity in the average relationship is much higher than 0.3%.

Failure: Vasectomy or tubal ligation which is best?

Although no procedure is 100% effective, men can be reassured vasectomy is more reliable at preventing pregnancy than all other forms of female birth control. Vasectomy is equally effective as female tubal ligation and intra-uterine contraception (IUD).

When a tubal ligation fails the woman will either become pregnant with a normal pregnancy or, more likely, pregnant with a life threatening ectopic (tubal) pregnancy. When a vasectomy fails most often nothing will happen and, in the worse case scenario, a normal intrauterine pregnancy will occur. This is why vasectomy is thought to be safer than tubal ligation.

The no-scalpel technique using coagulation to the proximal end and fascial interposition is designed to minimize reconnection of the divided ends by accelerating fibrosis and closure of the upper end with coagulation and by physically separating the two ends by interposing fascial connective tissue so granulation reconnection of the ends is much more difficult.