Vasectomy is one of the most effective forms of birth control available, but pregnancy after vasectomy is possible.
We discuss how a woman can still become pregnant after a vasectomy in more detail below, but here are the most important things to know:
- There no way to be 100% certain a man is sterile (unable to conceive) until semen analysis has shown he has a zero sperm count.
- You must use alternate forms of contraception until laboratory tests confirm sperm is not present in the man’s semen.
If you follow these guidelines, the chances of conceiving after a vasectomy are extremely low, but it’s still important to understand the risks.
How is pregnancy after vasectomy possible?
There are three primary ways a pregnancy can occur after a vasectomy:
- Having sex without contraception before the man’s sperm count is confirmed to be zero
- Natural reversal, also known as recanalization
- Surgical error
Sperm still present in semen (non-zero sperm count)
After a vasectomy, live sperm may still be present in a man’s semen for a number of months. This means that there is still a risk of impregnating a woman after the operation. Alternate contraception must be used until there is no sperm present (azoospermia).
Most doctors advise their patients that they should be sterile after two to three months and/or 20-25 ejaculations, but these are simply guidelines. It is still possible for a man to get a woman pregnant even if he is outside of these ranges. This is why doctors generally instruct their patients to have at least one semen analysis performed by a lab at some point after their operation. A sperm count is the only way to be certain a man is sterile.
When a pregnancy occurs after vasectomy due to unprotected intercourse before the “all clear” is given, it is known as a “technical error”. While most men understand that they can still get a woman pregnant immediately following their vasectomy, a surprisingly large portion of men (40% to 50%) don’t go back for a semen analysis.
Recanalization (spontaneous natural reversal)
A recanalization occurs when sperm are able to escape from the cut end of the vas deferens due to microscopic channels which have formed in the patient’s scar tissue. These tiny channels may be the result of a sperm granuloma or other complication. If these microchannels develop and the two severed ends of the vas deferens are very close or touching, sperm may be able to travel from one section of tube to the other.
Recanalization which occurs early on will be discovered as part of the post-vasectomy semen analysis and occurs in less than 1% of vasectomies. However, it is possible (but unlikely) for recanalization to occur after the man has been given the “all clear.” Late recanalization are extremely rare and occur in approximately 1 out of 4000 vasectomies.
For more information this topic, read our article on post-vasectomy recanalization.
Although uncommon, it is possible for a vasectomy to fail due to a surgical error. This is why it’s important to find a skilled doctor who has a good track record and has performed numerous operations. General physicians will often offer vasectomy services, but it’s usually best to go with a urologist due to their higher levels of experience and specialization.
The risk of surgical error (however small it may be) is another reason why the post-vasectomy semen analysis is so crucial.
Chances of becoming pregnant after vasectomy
The vast majority of post-vasectomy pregnancies occur in the first few months after the operation when the man may still have active sperm in his ejaculate and the couple doesn’t use an alternate form of birth control. As mentioned previously, these are known as “technical failures” and are not the result of an unsuccessful operation.
Even taking into account these early failures due to “user error” the failure rate of vasectomy is still favorable to many forms of birth control. One CDC study looked at 1,000 couples and found that of the 11 failures, half occurred in the first three months and no failures occurred after 18 months. The Association of Reproductive Health Officials gives an overall first-year failure rate of .10%, or 1/1000.
If the couples use birth control until the man is cleared by semen analysis, the risk of getting pregnant after vasectomy goes down to 1/2000 (.05%).
These figures will vary depending on the source and the parameters of the study, but the general consensus is that when a man follows his doctor’s post-operative instructions carefully and waits for the all clear before having unprotected sex, the chances of conceiving after vasectomy are very low.
It’s important to note that many studies on vasectomy failure were performed before the advent of new surgical techniques such as thermal cautery and fascial interposition. These new methods have further increased the effectiveness of vasectomy and have brought the recanalization rate even closer to 0%.