A sizable minority of men receiving vasectomy by simple ligation and excision—perhaps the most commonly performed male sterilization technique in low-resource settings—may still be at substantial risk for fertility six months after the procedure. Of more than 200 participants in a prospective study in Mexico,1 17% had not achieved sperm clearance by 24 weeks, according to semen analysis.

Although male sterilization is a highly effective and permanent form of contraception, men who have just undergone the procedure must typically use a backup method until semen analysis confirms the absence of sperm. In low-resource areas, however, such testing is often unavailable; thus, men are told to follow current clinical guidelines—to use backup for 10-12 weeks, or until they have ejaculated 15-20 times.

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.