A vasectomy is considered a permanent method of birth control. A vasectomy prevents the release of sperm when a man ejaculates. During a vasectomy, the vas deferens from each testicle is clamped, cut, or otherwise sealed. This prevents sperm from mixing with the semen that is ejaculated from the penis. An egg cannot be fertilized when there are no sperm in the semen. The testicles continue to produce sperm, but the sperm are reabsorbed by the body. (This also happens to sperm that are not ejaculated after a while, regardless of whether you have had a vasectomy.) Because the tubes are blocked before the seminal vesicles and prostate, you still ejaculate about the same amount of fluid.