A vasectomy (male sterilization) is a form of contraception that involves surgically cutting or blocking the tubes that transport sperm from the testicles to the penis. When men undergo a vasectomy their sperm can no longer reach the semen, as a result any semen that is ejaculated during sex does not contain sperm - which is needed to fertilize a woman's egg. A vasectomy is a very effective and permanent means of preventing pregnancy. It is estimated that only one out of every 2,000 men who receive a vasectomy will impregnate a woman during their lives. Vasectomy reversal reconnects the pathway for the sperm to get into the semen. Most often, the cut ends of the vas are reattached. In some cases, the ends of the vas are joined to the epididymis. These surgeries can be done under a special microscope ("microsurgery"). When the tubes are joined, sperm can again flow through the urethra.There are many reasons to undo a vasectomy. You might remarry after a breakup or have a change of heart. Or you might want to start a family over after the loss of a loved one.