Follow-up is an important part of a vasectomy

A study in the May 2025 issue of The Journal of Urology estimates that the failure rate of vasectomies performed in the United States is 1.97 per 1,000, or 0.58 percent – about four times larger than a previous estimate of one per 2,000.

The article’s authors called failure “rare,” despite the higher estimate, and said vasectomy is much better than other methods of male contraception. For their study, they defined failure as a pregnancy within six months of vasectomy. Health insurance data from 489,277 men who had a vasectomy was analyzed. They found 70.3 percent of the procedures were done by urologists in an outpatient setting. Failure rate was higher for vasectomies not done by a urologist and for men who didn’t verify the procedure worked with a subsequent semen check.

Importance of Testing

Urologist Brian Kowal, MD, of Urology Associates of Cape Cod, said getting at least one semen check after vasectomy has been a standard recommendation to patients. He said his office doesn’t process samples, so men must get them to a lab within an hour of ejaculation.

According to American Urology Association guidelines, a negative sample contains no sperm or less than 100,000 non-motile sperm per milliliter. The tests should be done within eight to 16 weeks after vasectomy, and repeated if positive. Until they get a negative result, men are counseled to keep using contraception. The presence of motile sperm six months afterwards is considered a failed vasectomy, and a second operation would be considered.

“It’s the patient's responsibility to get tested,” Dr. Kowal said of patient compliance, adding he assumes men are motivated to get tested to avoid an unintended pregnancy.

“Despite flawless technique, failures can occur with any surgeon,” he said. “This is why verifying the result is essential.”

Research articles indicate a sizeable percentage of men do skip follow-up tests. A March 19, 2025, article in Andrology looked at the compliance of 2,567 men who underwent vasectomy and reported 42.1 percent didn’t return for a semen check. Of those who did get an initial test that showed sperm still present, 43.3 percent didn’t come back for a second test. A December 2020 paper in European Urology Open Science said that patient compliance “has historically been low.”

Vasectomy Methods

Vasectomies aim to prevent flow of sperm from the testicles via two tubes (one on each side of the scrotum) called vas deferens. According to the American Urology Association, the procedure severs the vas and the cut ends are:

• Cauterized.
• And/or clamped with clips or tied off with sutures, in some cases after first being folded back on themselves.
• In addition, a segment of the vas between the cut ends may be removed or fascial tissue placed between the cut ends as a physical barrier.

Failures could occur from a surgical error, anatomical differences or the vas may regrow, a process called recanalization. According to a March 2024 issue of Frontiers in Medical Case Reports, even after a negative sperm check has been confirmed, the remote chance of recanalization occurring and causing pregnancy still exists.

It cited the case of a man who had a vasectomy in which a one-centimeter segment of both vas had been removed, and the cut ends cauterized and clamped with clips. He had a negative semen test post-surgery. Yet, 13 months later, his wife became pregnant and a semen test showed presence of active sperm. Before opting to redo the vasectomy, subsequent semen tests at six months, 25 months and 32 months had negative results. The authors said the case was the only known report of a recanalization subsequently becoming sterile.

Estimates Vary

Dr. Kowal said the accuracy of vasectomy failure rates would depend upon the quality of data and methods used. The authors of the May 2025 study said they found little current data on failure rates and described existing estimates as usually based on old information.

According to AUA guidelines published in 2012 in The Journal of Urology, the estimated failure rate is one in 2,000. The Eunice Kennedy Shriver National Institute of Child Health and Human Development cites a rate triple that on its vasectomy webpage: 15 per 10,000 (equivalent to 3 in 2,000) in a year after vasectomy. Planned Parenthood’s webpage comparing birth control methods says vasectomy is 99 percent effective, similar to female methods of contraceptive implant, IUD, and tubal ligation. Two other male methods, condoms and withdrawal, were rated as 87 percent and 78 percent effective.

Although vasectomies may be able to be reversed, Dr. Kowal said they are meant to be considered a permanent method of birth control.