Vasectomy does not result in immediate sterilization. Sperm may live for more than a week in the vas deferens, between the sutured ends and the ejaculatory ducts that lead to the penis. For most men, it takes 10 to 14 ejaculations and 1 to 2 weeks before the ducts are free of sperm. Usually, at least two semen samples are produced and collected for analysis 1 to 3 months after the procedure. When sperm count is zero, the man is sterile. Men who undergo any sterilization procedure (e.g., vasectomy, no-scalpel vasectomy) should use another form of birth control until semen analysis confirms sterility.
After sterility, semen is still ejaculated, but it lacks sperm. The testes continue to produce sperm, but sperm are prevented from reaching the prostate because they are blocked in the tied-off vas deferens, where they die and are absorbed into the body. Because semen is about 5% sperm, there is no discernible difference in the amount of semen ejaculated after vasectomy. The procedure does not affect testosterone production or libido.