Vasectomy takes weeks to become effective, since sperm remain within a man's
reproductive tract long after the procedure. Recent research suggests that it may take
longer than previously thought for sperm to disappear completely, and that some men
rebound to high sperm counts after sperm counts decline.
While guidelines vary, couples are often advised to use another method until 20
ejaculations or 12 weeks have passed. However, in a recently completed study by FHI and
AVSC International (AVSC), 44 of 198 men did not achieve azoospermia during 24 weeks of
follow-up after their vasectomies. Also, there was more variability in the time and number
of ejaculations before men reached azoospermia than had been anticipated. Most of the 44
men, however, had very low sperm counts by 12 weeks, probably low enough to prevent
pregnancies.
Another group of 18 men in the same study were considered, based on semen samples, to
be vasectomy failures. Sixteen of the 18 men had low sperm counts or no sperm during the
early period of follow-up, but later rebounded to higher counts. These findings suggest
that the vas may grow back together in some men, a process called recanalization.1
"Couples who are considering vasectomy should understand that it may take a long
time to become effective and failures do occur," says Dr. Laneta Dorflinger, FHI vice
president for research and development. "While this study is relatively small and
more research is needed to resolve many important questions, our current advice is to be
sure clients do not get the mistaken impression that vasectomy is effective immediately
and is always perfect, that it never fails."
Currently, couples are told that vasectomy has a reported failure rate of less than 1
percent. Thus, if a woman married to a vasectomized man gets pregnant, some people might
assume that the woman has been unfaithful. Women who become pregnant due to a vasectomy
failure could be physically harmed or ostracized by husbands or family members who think
incorrectly that vasectomy always prevents pregnancy.
While it is premature to recommend any changes in current guidelines for clinical
practice, Dr. Dorflinger says providers not already doing so may wish to consider two
options. Where practical, taking one or more semen samples at different times following
the procedure may help determine whether a man's vasectomy was successful, she says, and
the chance of recanalization may be lessened by the use of fascial interposition, where
the fascia is folded back over the vas to separate the two cut ends.
In another small study, to be published in the journal Contraception, four of 38 men
did not reach azoospermia within 24 weeks. A fifth man who had been azoospermic at weeks
two, three and four following the vasectomy reported that his partner became pregnant
after the study ended. At the end of the study, there were three vasectomy failures.
"The high rate of vasectomy failure may have occurred due to the fact that neither
fascial interposition nor cautery of the vas were used," says a report on the study,
which was coordinated by FHI and AVSC.2
In a vasectomy, the vasa deferentia are cut, keeping sperm from going from the
testicles to the urethra during ejaculation. Various techniques are used to close the vas
(occlusion). Most doctors in developing countries, where the two studies were done, are
trained to use ligation and excision, a tying of the vas using thread or sutures and
removal of about 1 cm of vas. Other techniques, which may close the vas more thoroughly,
include fascial interposition; electrocautery, which requires a tool not normally
available in resource-poor settings; and titanium clips. In developed countries like the
United States, urologists generally use one or a combination of these other techniques.
Well-controlled clinical trials comparing the effectiveness of different occlusion options
have not been done.
"Research should pursue several possibilities to address concerns raised by these
studies," Dr. Dorflinger says, including an evaluation of occlusion procedures being
used and the relationship of low sperm counts, sperm viability and sperm motility to
pregnancy rates, since azoospermia (the complete absence of viable sperm in ejaculate) is
probably not necessary to achieve effective contraception.
One study has examined the risk of pregnancy among men with low sperm counts who used
an experimental male hormonal contraceptive. The World Health Organization found that
following weekly injections of testosterone enanthate, partners of men with between
100,000 and 3 million sperm per milliliter of ejaculate (called oligospermia) had a
pregnancy rate of 8.1 percent, similar to some other contraceptive methods. Partners of
men who were azoospermic had a pregnancy rate of zero.3
Further studies are needed to establish a long-term pregnancy rate after vasectomy.
-- William R. Finger
References
- Family Health International. Time to Azoospermia
After Vasectomy: Expanded Study -- Final Report. Research Triangle Park, NC: Family
Health International, 1997.
- Cortes M, Flick A, Barone MA, et al. Results of a pilot
study of the time to azoospermia after vasectomy in Mexico City. Contraception,
1997 (in press).
- World Health Organization Task Force on Methods for the
Regulation of Male Fertility. Contraceptive efficacy of testosterone-induced azoospermia
and oligozoospermia in normal men. Fertil Steril 1996;65(4):821-29.
For more information, visit Family Health International's Website at www.fhi.org
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