Vasectomies Don't Always Prevent Pregnancy

May 5, 2004 -- As many as one in 100 vasectomies may fail to prevent pregnancy within five years of the procedure, a new study shows.

Researchers say that the study shows that like other birth control methods, vasectomies are not always 100% effective.

The study showed that six pregnancies were reported among 540 women within six weeks to 1.5 years after their husbands had a vasectomy.

"Couples considering vasectomy should be counseled about the small, but real risk of pregnancy following the procedure and that men are not sterile immediately after vasectomy," write researcher Denise J. Jamieson, MD, MPH, of the CDC, and colleagues.

A vasectomy is considered a permanent form of birth control to make a man unable to father a child. It is a surgical procedure in which the tube that carries the sperm from the testes to the urethra is cut or sealed off to prevent sperm from being released during ejaculation.

Vasectomies Not Fail-Safe

In the study, researchers followed a group of women whose husbands underwent vasectomy in five different medical centers in the U.S. from 1985 to 1987. The women were participants in the U.S. Collaborative Review of Sterilization (CREST) study and were interviewed by phone one, two, three, and five years after the procedure.

Researchers found that of the 540 women at risk for pregnancy, six pregnancies were reported after vasectomy and were considered caused by failure of the procedure. Three of the pregnancies occurred within three months of the vasectomy.

The results appear in the May issue of Obstetrics & Gynecology.

Although the women were not specifically asked, two of them reported that their husband did not follow the urologist's instructions regarding abstinence or use of back-up contraception. A common recommendation is to have semen analysis performed three months after vasectomy or after 20 ejaculations and to avoid intercourse or use another birth control method until no sperm has been documented.

Researchers estimated that around one in 100 vasectomies would fail within one to five years of surgery. They say those failure rates are similar to those reported in two prior studies on vasectomy failure.

Vasectomy vs. Tubal Ligation

The rates are also comparable to failure rates following tubal ligation (a female sterilization procedure also known as having the tubes tied) found among women in CREST.

Researchers say this is the first major study to compare pregnancy rates for female vs. male sterilization procedures.

"Couples who are considering sterilization should be counseled that both male and female sterilization are highly effective methods of permanent contraception but that pregnancies can occur," conclude the researchers.