Vasectomy is a minor procedure for men that is performed to divide the vas deferens from each testicle, stopping the flow of sperm to avoid pregnancy. After the vasectomy, the patient will have some sperm which were already stored in the seminal vesicles and prostate. It usually takes at least 15 to 20 ejaculations to eliminate the stored sperm. The sperm check examines the semen under the microscope to make sure that all of the sperm have been eliminated and the patient can no longer cause a pregnancy.
After vasectomy, about 70% of men will have negative sperm checks after 30 ejaculations. However, it can take over six months for some men to completely empty the seminal vesicles of sperm.