A vasectomy may be the most permanent method of birth control available today. A vasectomy prevents the release of sperm when a man ejaculates. Our physicians have performed thousands of vasectomies during their careers. 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. It usually takes several months after a vasectomy for all remaining sperm to be ejaculated or reabsorbed. You must use another method of birth control until you have a semen sample tested and it shows a zero sperm count. Otherwise, you can still get your partner pregnant.