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Pregnancies More Common than Expected after Vasectomy -- September 10, 2001

KATHMANDU, Nepal -- A recent study of Nepalese men who had been sterilized with a form of vasectomy (male sterilization) widely used in developing countries has found that the pregnancy rate is higher than previously thought. The study included 1,052 men who had had a vasectomy between one and four years ago.

The study, undertaken by Family Health International (FHI), in collaboration with the Ministry of Health, His Majesty's Government (HMG) of Nepal, estimated a first-year pregnancy rate of 17 per 1,000 among wives of men having ligation and excision vasectomies. That is, among 1,000 couples using this particular form of vasectomy for family planning, 17 women would become pregnant during the first year following the procedure. "This contrasts with an estimated pregnancy rate of 1 to 2 per 1,000 vasectomies in the United States, where different vasectomy procedures are typical and where couples are much older," reported Hanif Nazerali, FHI’s principal investigator for the study.

Compared with other forms of family planning, the vasectomy procedure used in Nepal is still quite reliable. For example, for couples using the Copper T intrauterine device, considered a very effective contraceptive method, approximately 8 women per 1,000 users will experience an unintended pregnancy during the first year. And for couples using condoms, approximately 30 to 140 women among every 1,000 become pregnant during the first year.

"This study is unique in that it is the first time that we have attempted to evaluate the effectiveness of vasectomy in a large sample of men from diverse areas in Nepal," says Dr. Kalyan Raj Pandey, a research member of the study, President of the Nepal Medical Association and advisor to the Ministry of Health.

"The results of the study in Nepal are not very different from what we are finding in some other developing countries when simple ligation and excision are used," reports Dr. David Sokal, a medical director at Family Health International. "While a vasectomy procedure is an excellent method of family planning, it's important that couples understand there is a small but real possibility of pregnancy after vasectomy."

"The study findings have important implications for counseling, follow up and clinical training," notes Dr. Laxmi Raj Pathak, another member of the research team and director of the Ministry of Health's Family Health Division.

Vasectomy is a permanent form of contraception in which the vasa deferentia — the tubes that carry sperm from the testes — are occluded (closed), either by ligation or other means. In developing countries, ligation (tying) and excision (removal) of a small length of the vas is the most common method of occlusion. In the United States and other high-resource settings where vasectomy is popular, cautery (burning) or metal clips are the most commonly used methods to occlude the vas.

Family planning handbooks typically describe vasectomy as nearly perfect, better than 99 percent effective at preventing pregnancy. However, different ways of performing a vasectomy may result in slightly different pregnancy rates.

In a related study, specifically designed to compare two different vasectomy techniques, preliminary results being released later this month show conclusively that sperm counts decrease more rapidly when a surgical technique known as fascial interposition is added to the simple ligation and excision technique. That study was conducted in Nepal and six other countries. Most of the men in the study announced today in Nepal had undergone vasectomy using simple ligation and excision, but without fascial interposition. Fascial interposition is a procedure in which the sheath covering the vas is pulled over one severed end and sewn shut to create a natural tissue barrier. The seven-country study looked at multiple sperm counts in each man, rather than pregnancy rates.

In the study reported today, researchers contacted men who had had a vasectomy one to four years ago, and asked each of them to provide a single semen sample for laboratory analysis. The men were also asked whether their wives had become pregnant. The men in the study were chosen from over 30,000 men who had had vasectomies between 1996 and 1999. The four Hill Districts of Bhojpur, Doti, Ramechhap and Tanahu were chosen randomly to represent the Development Regions. A proportionate sample of men were then selected randomly from within these districts. About 75 percent of vasectomies performed in Nepal are done in the Hill Region.

Twenty three men, or 2.3 percent, still had sperm in their semen, and 38 men reported that their wives had become pregnant during the years since their husband’s vasectomy. Pregnancies were more common among the younger women in the study. Eight of the pregnancies occurred within three months of the vasectomy, before a vasectomy is considered to be effective. A life-table calculation gave an estimate of a cumulative pregnancy rate of 4.2 percent at the end of three years (42 among every 1,000 women) or about 1 percent per year.

"It is quite possible that the pregnancy rate following vasectomy in the United States is an underestimate," said Hanif, FHI’s principal investigator. "If couples believe that vasectomy is 100 percent effective, a subsequent pregnancy would infer infidelity, and may go unreported. We would need systematic follow-up, with counseling, to improve our estimates."

Most of the pregnancies reported in Nepal were probably due to recanalization — the body healing itself — rather than surgical errors. Also, most couples in this study were relatively young compared to couples having vasectomies in the United States and other developed countries, which means they would be more fertile than older couples, and would remain fertile for more years after vasectomy than older couples. The process of recanalization can begin when sperm from the open ends of the vas leak out and cause a mild inflammation. This results in a condition known as a sperm granuloma, which is part of the body’s healing process. A granuloma is made up of white blood cells and other cells involved in the body’s healing process. The healing process can lead to the formation of a honey-combed "bridge" that can sometimes connect the two severed ends. Viable sperm can then cross and make their way to the other end.

Recanalization is often not a permanent condition. Often, the "bridge" will eventually solidify as part of the healing process, and scar tissue (fibrosis) will close off the recanalization. Simple ligation and excision appears more likely to lead to recanalization than other vasectomy methods.

In Nepal, where semen testing is generally not available, men are advised to wait 12 weeks before relying on their vasectomy. Until that time, couples are advised to use other contraceptive methods, such as condoms.

This study included two special features: (a) rigorous quality control of the semen testing; and (b) Internet-based data entry. Semen samples obtained in the Hill Districts of Nepal were preserved and analyzed in Kathmandu, and then results were validated by a U.S. laboratory. To facilitate data collection and analysis, this study used an Internet link for data entry, from Kathmandu to FHI's office in North Carolina, USA. This was the first study that FHI conducted using the Internet inthis way.

This study was supported in part with funds from the U.S. Agency for International Development.