Vasectomy is one of the most effective forms of birth control available, but conceiving a child after a vasectomy is possible. There are three primary ways unintended 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.Suggested reading
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.1
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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 that have formed in the patient’s scar tissue. These tiny channels may be the result of a sperm granuloma or other complications. 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 the 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 is extremely rare and occurs in approximately 1 out of 2000-3000 vasectomies.2Suggested reading
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 efficacy of vasectomy is still favorable to many forms of birth control. The early failure rate of vasectomy is in the range of 0.3–9% and the late failure rate is in the range of 0.04–0.08%.3 If birth control is used until the man is cleared by semen analysis, the risk of unwanted pregnancy after a vasectomy will go further down.
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.
Chances of unintended pregnancy after a vasectomy are extremely low. But it’s important to keep in mind that:
- 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.
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- Bradshaw A, Ballon-Landa E, Owusu R, Hsieh T-C. Poor Compliance With Postvasectomy Semen Testing: Analysis of Factors and Barriers. Urology. February 2020:146-151. doi:10.1016/j.urology.2019.10.026
- Labrecque M, Hays M, Chen-Mok M, Barone MA, Sokal D. Frequency and patterns of early recanalization after vasectomy. BMC Urol. September 2006. doi:10.1186/1471-2490-6-25
- Zini A, Grantmyre J, Chan P. CUA guideline: Vasectomy. Can Urol Assoc J. 2016;10(7-8):E274-E278. doi:10.5489/cuaj.4017