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SAN ANTONIO -- Vasectomy failure occurs more often than previously recognized but remains very uncommon, a large retrospective study showed.

An analysis of almost 500,000 cases showed a post-vasectomy pregnancy rate of 2.26 per 1,000 person-years and a birth rate of 1.24 per 1,000 person-years. Though still very low, the pregnancy rate exceeded historical estimates of about 1:2,000 cases and a repeat procedure rate <1%.

An analysis adjusted for baseline characteristics showed an increased risk of failure when a non-urologist performed the procedure and with an absence of a post-vasectomy semen analysis (PVSA), reported Albert S. Ha, MD, of Stanford University Medical Center in California, at the American Urological Association (AUA) annual meeting.

"The one thing I want to emphasize is the absolute failure rates are still very low, but it's still a little bit higher than we initially anticipated," Ha told MedPage Today. "One big takeaway from the study is that we're probably not utilizing post-vasectomy analyses enough to make sure that a lot of these men are clear. It's one of the things we need to work on."

"The other thing is that there is some heterogeneity in the quality of vasectomy in terms of the number of repeat procedures per year, urologists versus non-urologists," he added. "If people are going to do this procedure, they should be highly trained and know exactly what the techniques need to be and to make sure the quality of the procedure is the best possible."

A substantial proportion of vasectomies are performed each year by non-urology surgeons, non-surgeon physicians, and even advanced practice providers, Ha added.

Jesse Mills, MD, of the University of California Los Angeles, who moderated the presentation, also had two takeaways from the study.

"Even with the [failure] rates being maybe not 1 in 2,000, vasectomy is still by far the most effective permanent form of birth control," he told MedPage Today. "The second relates to how we counsel patients; nothing is 100%. You need to follow up with the post-vasectomy semen analysis, because if you do that, the rates can drop almost to zero."

Adjusted pregnancy rates will often be higher than estimated or expected because of numerous potential confounders, Mills added. A major confounding factor is the non-paternity pregnancy rate, which has been upwards of 20% in some studies.

"Not every person that has a vasectomy partner will have a pregnancy by the person that had the vasectomy," he noted.

Ha said the study had its genesis in the need for contemporary data on vasectomy failure. To examine the issue, he and his team performed a retrospective cross-sectional study using a national commercial claims database. They identified men who had vasectomies from 2007-2021. For purposes of the study, they defined pregnancy as all live births and losses and vasectomy failure as conception at least 6 months after vasectomy or a repeat procedure within 1 year of the initial procedure.

The analysis included 489,277 men who had a median age of 38; 85.4% of the patients had two or more children. Urologists performed 70.3% of the procedures, and post-vasectomy semen analysis was documented in 25.4% of cases.

In addition to the primary analysis, the investigators performed a post-vasectomy trend analysis. They found that pregnancy and live birth rates decreased significantly (P=0.002 and P=0.007, respectively) over the time frame of the study. Specifically, the data showed substantial declines coinciding with the introduction of AUA vasectomy guidelines in 2012 and a revision published in 2015.

The association with the guidelines suggests uptake of standards for procedures and follow-up, which might have reduced heterogeneity and improved quality, said Ha.

The trend analysis also showed that post-procedure conception rates declined substantially beyond 6 months after vasectomy. Pregnancy and birth rates were highest during the first 4 months after vasectomy (4.7 and 2.51 per 1,000 person-years, respectively), underscoring the need for PVSA to help rule out vasectomy failure, said Ha.

In an unadjusted analysis, the likelihood of vasectomy failure decreased with increasing age of the patient's partner and during later years of the study period (P<0.0001). Those associations disappeared in an adjusted analysis.

PVSA also proved to be a predictor of vasectomy failure, increasing with failure to perform the analysis (OR 1.16, 95% CI 1.06-1.26, P=0.0008). In the unadjusted analysis, no difference existed between urology and non-urology practitioners, but the adjusted analysis showed a significantly higher risk of vasectomy failure when non-urologists performed the procedure (OR 1.56, 95% CI 1.40-1.74, P<0.0001).

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