Our results indicate that cautery is a highly effective and safe method to occlude the vas for vasectomy. Results of this prospective study found that vasectomy failure, based on semen analysis results, is rare (0.8%). In addition, no serious adverse events related to the vasectomy procedure were reported.
The published literature on cautery occlusion methods is difficult to interpret and evidence-based conclusions on effectiveness of cautery for vas occlusion are difficult to make . Even in the U.S., a variety of vas occlusion methods are used  which may be a reflection of the limited quality of data to support the use of any one occlusion technique. In 1995 (the latest national data available), 71% of vasectomies in the U.S. were done using cautery, up from 50% in 1991 [10, 14].
In 10 published studies comparing ligation and cautery as methods of vas occlusion, the failure rates based on semen analysis ranged from 0–5% for cautery occlusion . Results of the two best quality studies comparing ligation and excision to cautery (rated by the review paper's authors as moderate quality) are conflicting; one study found a higher failure risk based on semen analysis for cautery  and the other found a lower risk .
Men appear to reach azoospermia sooner in terms of both time and number of ejaculations following vasectomy by cautery compared to ligation and excision. When ligation and excision (with or without fascial interposition) were used, the probability of achieving azoospermia was in the range of 60–70% at 12–14 weeks postvasectomy [7, 8, 16]. We found that with cautery occlusion the probability of achieving azoospermia was 85% at 12 weeks. Edwards reported 100% azoospermia by 14 weeks with cautery occlusion . Men may also reach severe oligozoospermia (< 100,000 sperm/mL) faster with cautery; the probability of success at 12 weeks was 95% in our study, compared to recently published results of 91% at 14 weeks for ligation and excision with fascial interposition and 82% for ligation and excision without fascial interposition .
The semen analysis patterns seen in the two vasectomy failures which were not technical failures are suggestive of very early recanalization given the extremely low sperm numbers at 2 weeks followed by a gradual increases back into the range of normal or potentially fertile sperm counts (see Figure 2). This is similar to the patterns reported for vasectomy failures when ligation and excision were used . This concept of very early recanalization–rapid declines in sperm numbers in the first few weeks after vasectomy followed by a gradual rise back to the normal range–has not been widely commented on in the literature, most likely because early and frequent semen analyses after vasectomy are unusual. An additional strength of this study was that semen analysis follow-up continued after men achieved azoospermia. This is unusual in the published literature on vasectomy and provides a more detailed profile of sperm concentrations of men following vasectomy.
Ideally, vasectomy success is confirmed by semen analysis. In many low resource settings, however, semen analysis is not readily accessible or available. Protocols commonly used in these settings recommend 10–12 weeks or 15–20 ejaculations as endpoints for when men can begin to rely on their vasectomy for contraception [18, 19]. Our data confirm results of two recent studies which also showed that 12 weeks after vasectomy is more reliable than 20 ejaculations as an endpoint and should reduce the risk of failure [7, 8]. Our finding that the predictive value of one sample at 12 weeks for success at the end of the study was 99.7% has practical implications for vasectomy services. First, it suggests that one semen analysis at 12 weeks should be sufficient to indicate whether or not a man could begin to rely on his vasectomy for contraception, and second, it is further evidence that 12 weeks is a reasonable endpoint when semen analysis is not available, if cautery is used as the occlusion method.
Younger age accelerated success, with men younger than 35 years of age achieving both severe oligozoospermia and azoospermia sooner than older men. A similar age effect was seen when ligation and excision was used . However, although statistically significant, the clinical significance of the age effect, at least with cautery occlusion, is likely to be minimal given the small absolute differences in probability of success between the age groups (see Table 2).
Our study was not designed to analyze the efficacy of the various occlusion procedures used at the study sites, but rather to estimate effectiveness of occlusion techniques that include use of cautery. Given the differences in the occlusion techniques used at the study sites (see Figure 1), it was not possible to determine any effect of the specific aspects of the techniques (such as fascial interposition or removal of a segment of vas), on overall success or failure. The two failures that occurred due to apparent recanalization were at the site using electrocautery without fascial interposition or excision of a segment of the vas. Which of the three specific aspects of the occlusion procedure may have contributed to the vasectomy failures cannot be determined.
The existing evidence in favor of using fascial interposition with cautery is weak . However, fascial interposition has been shown to significantly improve the success of vasectomy by ligation and excision . Even fewer data are available regarding differences in the effectiveness of thermal and electrocautery. A very small study found that vas occlusion was more complete based on histologic exam when thermal cautery was used  and a non-randomized comparative trial found a higher, but nonsignificant, risk of failure with electrocautery compared to thermal cautery .
Data on the importance of removing a segment of the vas are also limited. A recent study found no association between the length of vas excised and the risk of recanalization  and success has been reported when no vas tissue is removed with occlusion by cautery combined with fascial interposition [5, 22–24]. Clearly, additional study is needed before any evidence-based conclusions can be made about the importance of the type of cautery, use of fascial interposition, and excision of a segment of the vas in reducing the risk of vasectomy failure.
One limitation of our study is that data are based on semen analysis as opposed to pregnancy. The risk of pregnancy associated with oligozoospermia following vasectomy–including the minimum sperm concentration that could lead to pregnancy–is not well characterized. Results from a study of male hormonal contraception showed that it is necessary to reduce sperm counts to under 3 million per mL to achieve reliable contraception in men with proven fertility . These results, however, might not be strictly comparable to the situation following vasectomy. None the less, it is clear that the three vasectomy failures seen here had sperm concentrations well within the fertile range (Figure 2).
In addition, it is possible that recruitment bias could have affected the study results. There was a wide variation in the percent of men who agreed to participate in the study (U.K. 98%, U.S. 96%, Brazil 70%, Canada 25%), which appears to have been related to the convenience of providing semen samples at the different sites. We have no information on men who declined to participate in the study, although there are no obvious reasons why study outcomes of the sort being measured here would differ systematically for men agreeing to participate relative to those who did not. We cannot, however, rule this out as a source of bias.