Every year an estimated half a million men have a vasectomy but nearly half of those men don't return for follow-up tests that make sure the procedure is working, new research suggests.
Those who don't go back, and therefore risk an unwanted pregnancy, are more likely to be smokers, not highly educated and the fathers of four or more children, the study found.
An increasing number of couples fail to use an additional form of contraception before the patient has been cleared, suggesting the need for better communication between doctors and vasectomy patients, especially those at higher risk of not following up, said study co-author Yefim Sheynkin, an associate professor of urology at the State University of New York at Stony Brook.
Overall, a vasectomy is a "pretty darned good" form of birth control, said Dr. John K. Amory, an associate professor of medicine at the University of Washington Medical School "It's about 99 percent effective."
In rare cases, a vasectomy fails. In those cases, sperm can make it into semen and impregnate a woman.
To make sure that any remaining sperm has cleared out of the vas deferens tubes, doctors routinely ask patients to provide a semen sample about three months after the vasectomy procedure, Amory said.
Total clearance usually takes 20 to 30 ejaculations, he said, noting sperm can stay alive for weeks.
"We want to see a sperm count of zero after three months," he said. "There are millions and millions of sperm. If only 1 percent of them are alive, that's still a lot."
Amory said about half of men fail to return for the follow-up test, and the new study confirms that number.
The researchers, who report their findings in the December issue of Contraception, examined the medical records of 214 vasectomy patients to see what role sociodemographic factors might play in follow-up.
Forty-six percent didn't get a post-vasectomy semen analysis. Age and marital status made no difference, but men who didn't return were less likely to be college-educated, the researchers found.
Doctors explicitly tell patients to return for a sperm check, but since the message is not getting across, there's talk of other strategies, Sheynkin said.
These might include making follow-up appointments at the time of a vasectomy and using home semen analysis tests that could serve as a solution for forgetfulness, inconvenience, and feelings of embarrassment.
The latter strategy is promising, said Amory. He envisions men buying test kits at the store or online, as women do with pregnancy tests.
SOURCES: Yefim Sheynkin, M.D., associate professor, urology, State University of New York at Stony Brook, and director, male infertility and microsurgery program, Stony Brook University Hospital; John K. Amory, M.D., M.P.H., associate professor, medicine, University of Washington, Seattle; December 2009 Contraception.
John C. Herr, director of University of Virginia's Center for Research in Contraceptive and Reproductive Health.