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To test the validity of 12 weeks and 20 ejaculations as cutoff
points, researchers enrolled men seeking a vasectomy at three public
clinics in Mexico City in 1995-1996, and followed them for up to 24
weeks after the procedure. Six experienced surgeons (two per clinic)—who
had attended a workshop designed to ensure use of a standardized
technique—performed a simple ligation and excision procedure.
The men returned to the clinic every other week to provide a semen
sample, which was examined microscopically for sperm concentration and
motility according to World Health Organization guidelines, and to
report the number of ejaculations since their most recent visit. Men
were considered to have achieved sperm clearance at their first of two
consecutive visits in which the semen sample contained no sperm.
The analysis included 217 men, aged 21-58 years (mean, 32 years). By
the end of the study, 78% of men had achieved sperm clearance and 17%
had not; 5% had dropped out or had been lost to follow-up. Of those
whose semen samples still contained sperm, fewer than one-third had
"persistent but low sperm concentrations," and were presumed to have had
a successful vasectomy with delayed sperm clearance; the remainder were
considered to have had a failed vasectomy. In the latter group, sperm
concentrations at 22-24 weeks were greater than three million sperm per
mL of semen, including active sperm; the average concentration was
greater than 39 million/mL, indicating "a significant risk for
pregnancy" for the patients' fertile female partners.
Time to sperm clearance varied widely. Sperm clearance was reached at
medians of 10 weeks and 32 ejaculations. At 12 weeks, 63% of patients
produced sperm-free semen; 13% had at least three million sperm per mL,
most of them more than 20 million/mL. At the 20th ejaculation, only 44%
of men produced sperm-free semen, whereas 21% had sperm concentrations
exceeding three million per mL.
Cumulative event probabilities estimated by life-table analysis
showed that sperm clearance was achieved by 60 per 100 study
participants at 12 weeks, and by 82 per 100 at 22 weeks. In addition,
the Kaplan-Meier cumulative event probability of achieving sperm
clearance was 28 per 100 men at the 20th ejaculation.
According to chi-square analysis, failure rates among individual
surgeons (range, 7-20%) did not differ significantly. However, each
surgeon performed only 29-45 vasectomies in the study, which may have
precluded the detection of meaningful differences.
The researchers believe that the most likely cause of vasectomy
failure in the study was reattachment of the severed vas ends soon after
vasectomy, noting that men with a failed vasectomy typically experienced
a brief, dramatic reduction in sperm concentration sometime in the early
postvasectomy period. Furthermore, they suggest that the high number of
such cases in the study "was likely related to the occlusion method
used." However, they say that they are unaware of any randomized,
controlled trial to date that has compared simple ligation and excision
with other techniques—for example, those in which the severed ends of
the vas deferens are sealed by applying surgical clips, by burning (or
cauterizing) the ends or by covering one end with the tissue layer
surrounding the vas.
According to the researchers, the study findings show that
"guidelines...based only on the time or number of ejaculations after
vasectomy cannot adequately replace semen testing when ligation and
excision are used." For situations in which semen testing is not an
option, they note that a cutoff of 12 weeks is probably more reliable
than that of 20 ejaculations, yet each "leaves a substantial number of
men at risk for continued fertility."
—C. Coren
1. Barone MA et al., A prospective study of time and number of
ejaculations to azoospermia after vasectomy by ligation and excision,
Journal of Urology, 2003, 170(3):892-896. |
