Objectives: To determine the incidence of positive semen analysis 12 months after vasectomy clearance.
Subjects and methods: A prospective study was undertaken, starting in 1990, of men undergoing vasectomy. Azoospermia was confirmed by two successive semen analyses 16 weeks after vasectomy. One year later a further sample was analysed for the presence of sperm.
Results: Of 1000 men who provided a sample for analysis, six men (0.6%) have had positive semen analyses 1 year after the initial tests showed azoospermia. In all six the sperm count was <10,000 per mL. Five of the six men produced a repeat sample 1 month later which, in all five cases, showed azoospermia. No pregnancies have been reported to date.
Conclusion: Transitory reappearance of sperm following successful vasectomy occurs in about 0.6% of men. This incidence is 18 times greater than the reported pregnancy rate following successful vasectomy.