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Vasectomy is a birth control method in which part of the vas deferens is surgically removed to prevent sperm from entering the ejaculate. Vasectomy does not affect the testicles nor the production of testosterone. Sexual desire and the ability to have an erection and an orgasm are not affected. Because the sperm itself makes up a very small proportion of the ejaculate, a vasectomy does not affect the volume or appearance of the ejaculate. If the vasectomy is successful, sperm can no longer be included in the ejaculate. They are broken down and absorbed by the body (more details).
Some sperm remain in semen for several ejaculations after a vasectomy. Therefore, it is critically important to examine semen specimens to ensure sterility. A British society of semen experts recommends using alternate methods of birth control for 16 weeks to avoid a post vasectomy pregnancy (assessment of post vasectomy PDF). They recommend the first vasectomy test at 16 weeks post vasectomy, a second vasectomy test at 18 weeks post vasectomy, and a third vasectomy test at one year post vasectomy.
Once semen specimens are free of sperm, most vasectomies are effective for life. The following studies outline the importance of post-vasectomy testing:
The Risk of Pregnancy After a Vasectomy
Sperm are produced in tubes (seminiferous tubules) within the testis. Most men produce billions of sperm every day. Once the sperm are mature enough to swim, they enter the epididymis, a small organ attached to the testicle. The epididymis connects to the vas deferens, the tube that carries sperm into the body to connect to the urethra for ejaculation. The seminal vesicles and the prostate contribute the fluid portion of ejaculated semen.
As noted in the diagram, it is the vas deferens that is cut during a vasectomy. This blocks sperm from entering the urethra, but does not interfere with the fluids produced by the seminal vesicles and prostate.
IT IS IMPORTANT TO NOTE THAT A SPERM STORAGE POUCH, THE AMPULLA, IS NOT BLOCKED BY THE VASECTOMY. SPERM STORED IN THE AMPULLA REMAIN VIABLE AND MOTILE FOR AN EXTENDED PERIOD OF TIME. THESE SPERM CAN PRODUCE A PREGNANCY UP TO SEVERAL MONTHS AFTER VASECTOMY.
Doctors performing vasectomies around the world report pregnancy rates varying from one to eleven pregnancies per every thousand vasectomies. ALMOST ALL "POST VASECTOMY" PREGNANCIES RESULT FROM UNPROTECTED SEX WITHIN THE FIRST FEW MONTHS AFTER VASECTOMY.
Rarely, the vas deferens can grow back together, usually within the first year, leading to viable sperm in semen. A repeat vasectomy can restore contraception. It is commonly agreed that a follow up semen analysis is the only way to confirm that a vasectomy was successful. But doctors do not always agree on when and how many semen specimens should be analyzed.
A British society of semen experts (the British Andrology Society) reviewed the vasectomy literature and in 2002 published their recommended guidelines:
IF NO SPERM ARE DETECTED IN BOTH SPECIMENS, THE VASECTOMY WAS SUCCESSFUL
Vasectomy in the United States, 2002 - “Poor compliance with follow up recommendations continues to be a problem…”
Pregnancy rates after vasectomy: a survey of US urologists
British Andrology Society guidelines for the assessment of post vasectomy semen samples (2002) P Hancock and E McLaughlin
Vasectomy Follow-up: Clinical Significance of Rare Nonmotile Sperm in Postoperative Semen Analysis
EVIDENCE-BASED CLINICAL PRACTICE