Tubal sterilizations don’t rule out ectopic pregnancy

A 32-year-old woman comes to your clinic with complaints of bleeding and lower abdominal pain. Her chart reflects a tubal sterilization at age 24, performed after she gave birth to her third child. What’s your diagnosis?

A recently released study indicates you should check for an ectopic pregnancy. While tubal ster-ilization is a safe and highly effective method of preventing pregnancy, it does fail sometimes. According to AVSC International in New York, because failure rates for female sterilization are relatively low (less than 2% over 10 years), the actual number of ectopic pregnancies also is quite low. But when pregnancy does occur, the risk that it will be ectopic is significant — about one in three. The new study indicates that the risk persists for up to 10 years after steriliza- tion.1 (Inserted in this issue of Contraceptive Technology Update are patient handouts on tubal sterilization and vasectomy. According to the authors of Contraceptive Technology, couples should consider both methods, because they are comparable in effectiveness and intended to be permanent.2)

"Before this study, we thought nearly all pregnancies that were going to occur occurred in the first year or two after the [sterilization] procedure," notes Herbert B. Peterson, MD, chief of the Women’s Health and Fertility Branch at the Centers for Disease Control and Prevention in Atlanta and lead author of the study. "With this study, we see that they continue to occur for many years after the procedure, and when we focused on ectopic pregnancy, we saw that the further from the sterilization that the pregnancy occurred, the more likely the pregnancy was to be ectopic."

Sterilization remains a safe, effective form of contraception, Peterson says, adding that providers and patients can use the study results to better weigh the risks and benefits of the method.

Long-term follow-up key to report

The study is one in a series of reports to be released from the U.S. Collaborative Review of Sterilization (CREST), a comprehensive overview of tubal sterilizations performed at nine medical centers across the country. (See CTU, August 1996, p. 94, for information on the initial report, published in the American Journal of Obstetrics and Gynecology.3 Findings from that research showed a 10-year cumulative failure rate of 18.5 pregnancies for every 1,000 tubal sterilizations, higher than past reports of four pregnancies per 1,000 procedures for one year after sterilization surgery.)

Women ages 18 to 44 were enrolled from 1978 to 1986, with follow-up completed in 1994. A total of 10,685 women were followed in the prospective cohort study. Sterilization was performed using one of six methods: bipolar coagulation, unipolar coagulation, silicone rubber band application, spring clip application, interval partial salpingectomy, and postpartum partial salpingectomy.

Cumulative life-table probabilities and proportional hazards analysis were used to determine the risks of ectopic pregnancy following steril-ization. With a total of 47 ectopic pregnancies occurring in the study population, researchers calculated the 10-year cumulative probability for all methods of sterilization at 7.3 per 1,000 procedures. The cumulative probability of ectopic pregnancy in the fourth through the 10th years following sterilization was significantly higher than the cumulative probability in the first three years: 5.3 per 1,000, compared with 2.0 per 1,000.

The probability of ectopic pregnancy varied substantially according to the sterilization method used, researchers found. For example, bipolar coagulation, the most popular technique used by U.S. providers, had the highest probability of failure: 17.1 ectopic pregnancies per 1,000 procedures, with postpartum salpingectomy ranked the lowest, at 1.5 pregnancies per 1,000.

Age at time of sterilization also proved to be a significant factor in the study. Women who chose sterilization before age 30 were nearly twice as likely as older women to experience an ectopic pregnancy, the analysis revealed.

For those women who were sterilized by bipolar coagulation before age 30, the risk of ectopic pregnancy rose dramatically. Analysis showed 10-year cumulative probabilities for this method at 31.9 per 1,000 procedures — 27 times as high as the 1.2 per 1,000 rate calculated for postpartum partial salpingectomy.

It is important to note that younger women are more fertile and have a longer span of fertility, Peterson says. Now that the CREST study has determined that pregnancies can occur not only within the first year or two, but as long as 10 years after the procedure, age at time of sterilization should be considered.

"We now find that a 25-year old woman really has at least 15 years over which she can get pregnant, and that’s why the cumulative risk is key," he says. "There are more years over which that cumulative risk can be spread."

Since age also factors into the possibility that a woman will regret using sterilization, most clinicians encourage women to use other forms of contraception as long as possible and to consider tubal sterilization as a last resort.4

Do results reflect today’s improvements?

The CREST study, with its long follow-up, has provided important information on the risks of pregnancy beyond the first year or two following sterilization. In turn, improvements in method techniques and increased provider training may make today’s procedures more effective.

"I think our understanding of proper technique has improved since some of those sterilizations were done, especially in terms of the coagulation techniques and the best places to put the rings," says Lynn Borgatta, MD, MPH, a medical research consultant for Planned Parenthood Federation of America in New York. "I think we know a little bit more about techniques since the beginning of that study, so that if people are well-trained and follow certain rules, then the rates shouldn’t be any higher."

Providers and patients need to weigh the risks and benefits of each sterilization method, just as they would for any other form of birth control, Peterson says.

In the study, for example, bipolar coagulation offered a higher risk of pregnancy than unipolar coagulation, yet unipolar coagulation is the technique most likely to result in serious injury or death.5 Both silicone band and spring clips have elevated pregnancy risks, yet they are the most easily reversible methods of sterilization. And while postpartum partial salpingectomy offers the lowest rate of ectopic pregnancy, women undergoing this procedure are 40% more likely to regret having been sterilized.6

"What the study is telling us is that there are advantages and disadvantages to each of the sterilization techniques," Peterson concludes. "We hope the study will help women and clinicians consider the relative advantages and disadvantages when they make their choices."

References

1. Peterson HB, Xia Z, Hughes JM, et al. The risk of ectopic pregnancy after tubal sterilization. N Engl J Med 1997; 336:762-767.

2. Hatcher RA, Trussell J, Stewart F, et al. Contraceptive Technology 16th ed. New York: Irvington Publishers; 1994, p. 380.

3. Peterson HB, Xia Z, Hughes JM, et al. The risk of pregnancy after tubal sterilization: findings from the U.S. Collaborative Review of Sterilization. Am J Obstet Gynecol 1996; 174:1,161-1,170.

4. Tulandi T. Tubal sterilization. N Engl J Med 1997; 336:796-797.

5. Peterson HB, DeStefano F, Rubin GL, et al. Deaths attributable to tubal sterilization in the United States. Am J Obstet Gynecol 1983; 146:131-136.

6. Wilcox LS, Chu SY, Eaker ED, et al. Risk factors for regret following sterilization: Five years of follow-up in a prospective study. Fertil Steril 1991; 55:927-933.