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Pregnancy After Tubal Sterilization With Silicone Rubber Band and Spring Clip Application

From the Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia; and the Office of Population Research, Princeton University, Princeton, New Jersey.

Address reprint requests to: Herbert B. Peterson, MD Centers for Disease Control and Prevention Division of Reproductive Health 4770 Buford Highway NE Mailstop K-34 Atlanta, GA 30341

	Abstract

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Objective: To determine risk factors for pregnancy after tubal sterilization with silicone rubber bands or spring clips.

Methods: A total of 3329 women sterilized using silicone rubber bands and 1595 women sterilized using spring clips were followed for up to 14 years as part of a prospective cohort study conducted in medical centers in nine US cities. We assessed the risk of pregnancy by cumulative life-table probabilities and proportional hazards analysis.

Results: The risk of pregnancy for women who had silicone rubber band application differed by location of band application and study site. The 10-year cumulative probabilities of pregnancy varied from a low of 0.0 per 1000 procedures at one study site to a high of 42.5 per 1000 procedures in the four combined sites in which fewer than 100 procedures per site were performed. The risk of pregnancy for women who had spring clip application varied by location of clip application, study site, race or ethnicity, tubal disease, and history of abdominal or pelvic surgery. The probabilities across study sites ranged from 7.1 per 1000 procedures at 10 years to 78.0 per 1000 procedures at 5 years (follow-up was limited to 5 years at that site).

Conclusion: The 10-year cumulative probability of pregnancy after silicone rubber band and spring clip application is low but varies substantially by both clinical and demographic characteristics.

Tubal sterilization is the most prevalent method of contraception in the United States, with more than 10 million US women having undergone the procedure.¹ Although most interval sterilizations are performed with bipolar coagulation,² large numbers of laparoscopic procedures using silicone rubber bands or spring clips are performed each year. A recent report from the US Collaborative Review of Sterilization³ found that the chance of pregnancy after laparoscopic sterilization was highest with spring clip application, followed by bipolar coagulation and silicone rubber band application. Notably, women sterilized at a young age (less than 28 years) had a 10-year cumulative probability of pregnancy of 5.2% after spring clip application and 3.3% after silicone rubber band application.³ In a separate report, we described in detail the risk of pregnancy after bipolar coagulation.⁴

In this report, we analyze data from the US Collaborative Review of Sterilization to describe risk factors for pregnancy after two mechanical methods of tubal occlusion commonly used for laparoscopic sterilization: silicone rubber bands and spring clips. We hypothesized that those procedures performed earlier in the study were more likely to result in pregnancy than procedures performed later, that women with tubal abnormalities would be more likely to become pregnant, and that the location of band or clip application would affect failure rates.

	Materials and Methods

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The methods of the US Collaborative Review of Sterilization have been described in detail elsewhere.^3–5 In brief, study enrollment occurred between 1978 and 1987, and follow-up was completed in 1994. Women undergoing silicone rubber band and spring clip application were first enrolled in 1979. Women eligible for enrollment were those aged 18–44 years undergoing a method of tubal sterilization under study in medical centers in nine US cities. The method of sterilization was chosen by the woman and her physician. The study protocol was approved by the institutional review board at each center, and all women enrolled in the study gave written informed consent.

Before sterilization, a detailed history of each study participant was taken by a trained nurse interviewer, who also recorded details of the sterilization procedure on the basis of direct observation or record review. The interviewer conducted follow-up interviews by telephone as well. The goal was to interview each woman at 1 month and annually for 5 years after the sterilization. In addition, women enrolled between 1978 and 1983 were eligible for a single follow-up interview at 8–14 years after sterilization. When a woman could not be contacted for follow-up, we used information provided in the last completed interview for analysis.

Women were asked at each follow-up interview whether, since the last interview, they had had a positive pregnancy test or had been told by a physician that they were pregnant. If they responded affirmatively, the nurse obtained detailed information about the pregnancy from the woman and, when available, from medical records. We used the best available information to determine whether the woman had indeed become pregnant and whether the pregnancy was a luteal phase pregnancy (ie, a pregnancy conceived before sterilization but identified after sterilization). Intrauterine and ectopic pregnancies were classified on the basis of reports of clinical examination, ultrasound examination, and pathologic examination, when those findings were available. If we were uncertain whether the pregnancy was conceived before sterilization, we classified the pregnancy as a luteal phase pregnancy, thus potentially underestimating the true number of sterilization failures. We discontinued follow-up with the first report of pregnancy, and also with a report of repeat tubal sterilization, tubal anastomosis, hysterectomy, or death. We considered these women at risk of pregnancy from the date of sterilization to the date of one of these events. If the date of the event was unknown, we considered these women at risk until the midpoint between the last interview before the event and the first interview after the event.

We restricted our analyses to women who had either silicone rubber bands or spring clips applied to both fallopian tubes. To estimate the risk of pregnancy separately for those enrolled earlier and later in the study, we compared women undergoing spring clip application in 1979–1983 with those undergoing the procedure in 1985–1987 (no women were enrolled in 1984). Because women enrolled in 1985–1987 were eligible for just 5 years of follow-up, we restricted our comparison of spring clip failure rates between those enrolled in 1979–1983 and those enrolled in 1985–1987 to 5 years of follow-up. We were unable to compare failure rates for silicone rubber band procedures by study period because the study sites were mutually exclusive for earlier and later periods (ie, no site in which silicone rubber band procedures were performed participated in the study during both study periods). We then estimated the 10-year cumulative probability of pregnancy for both spring clip application and silicone rubber band application for the entire enrollment period (1979–1987).

The cumulative probability of pregnancy was estimated using a standard life-table technique, and risk factors for pregnancy after sterilization were assessed using Cox proportional hazards analysis with the SAS statistical package (SAS Institute, Cary, NC). The only risk factor studied related to the location of silicone rubber band or spring clip application was whether the device was applied to the proximal, middle, or distal third of the fallopian tube or whether the device was applied to some combination of these sites.

	Results

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Among the 10,685 study participants who were eligible for analyses of pregnancy after sterilization once 178 had been excluded,³ 3329 underwent silicone rubber band application and 1595 underwent spring clip application (Table 1). Of the 3329 women who underwent silicone rubber band application, 35 (1.1%) became pregnant; 25 pregnancies were intrauterine and 10 were ectopic. The 10-year cumulative probability of pregnancy varied by age (as reported previously³) and by race or ethnicity: Black, non-Hispanic women had a higher probability (52.3 per 1000 procedures; 95% confidence interval [CI] 23.1, 81.4) than did white, non-Hispanic women (6.5 per 1000 procedures; 95% CI 1.4, 11.5; P < .01) or women who were Hispanic, American Indian, Alaskan Native, or Asian or Pacific Islander (5.1 per 1000 procedures; 95% CI 0.0, 12.0; P < .01). Although women with histories of pelvic inflammatory disease (PID) had a higher probability of pregnancy 5 years after sterilization (24.2 per 1000 procedures; 95% CI 7.5, 40.8) than did women without such histories (8.6 per 1000 procedures; 95% CI 4.5, 12.8; one-tailed P = .04), the cumulative probabilities at 10 years after sterilization were similar for both groups (24.2 and 28.3 per 1000 procedures, respectively; one-tailed P = .62).

The 10-year cumulative probability of pregnancy varied widely by study site, ranging from 0.0 per 1000 procedures to 42.5 per 1000 procedures (95% CI 0.0, 106.0). The highest probabilities of failure were seen in the four combined sites in which fewer than 100 procedures were performed per site (42.5 per 1000 procedures) and in two single sites: one with a rate of 40.8 per 1000 procedures (95% CI 0.0, 101.5) and the other (having only 5 years of follow-up) with a rate of 42.2 per 1000 procedures (95% CI 18.3, 66.0). The three sites with the lowest failure rates had a combined total of four failures among 1372 procedures.

We analyzed 12 factors to determine their effect on the relative risk of failure of silicone rubber band application: age at sterilization, race or ethnicity, study site, education, marital status, gravidity, history of PID, history of abdominal or pelvic surgery, type of anesthesia, presence of adhesions recorded at sterilization, tubal disease recorded at sterilization, and whether the band was applied solely to the distal portion of either fallopian tube. We found that only study site and distal application were significant by multivariable analysis (Table 2). Procedures performed in three sites with fewer than 100 procedures had a nearly 15-fold increase in the risk of failure relative to the risk in the three combined sites with the lowest failure rates. Procedures in which a band was applied solely to the distal portion of at least one tube had a nearly five-fold increase in the risk of failure relative to other procedures.

The 10-year cumulative probability of pregnancy varied by age (as reported previously³). Black, non-Hispanic women had a higher 10-year cumulative probability (59.5 per 1000 procedures; 95% CI 37.7, 81.2) than white, non-Hispanic women (11.8 per 1000 procedures; 95% CI 4.1, 19.5; P < .001); women who were Hispanic, American Indian, Alaskan Native, or Asian or Pacific Islander had the highest probability (194.2 per 1000 procedures), although that estimate was imprecise (95% CI 0.0, 401.0; P = .20 when compared with black, non-Hispanic women and P = .08 when compared with white, non-Hispanic women).

Women who had tubal disease recorded at sterilization had a much higher probability of pregnancy 1 year after sterilization (117.6 per 1000 procedures; 95% CI 9.3, 225.9) than did those without such a history (16.0 per 1000 procedures; 95% CI 9.6, 22.3; one-tailed P = .03). At 10 years, this difference was not significant (one-tailed P = .07). Because all of the pregnancies that occurred among women with recorded tubal disease occurred within 1 year after the procedure, the 10-year cumulative probability of pregnancy among women with recorded tubal disease was the same as the 1-year probability. The 10-year cumulative probability for women without recorded tubal disease (34.6 per 1000 procedures; 95% CI 23.5, 45.8) was only twofold greater than that (16.0 per 1000 procedures) for such women at 1 year after the procedure. Thus, although one failure of clip application occurred in the tenth year of follow-up, most failures in women with and without recorded tubal disease occurred within 1 year after the procedure.

The 10-year cumulative probability of pregnancy for procedures in which the clips were applied to the proximal third of both tubes was lower (29.5 per 1000 procedures; 95% CI 17.2, 41.8) than that for procedures in which at least one clip was applied to a location other than the proximal third (54.7 per 1000 procedures; 95% CI 31.8, 77.6; one-tailed P = .03). Procedures in which two clips were applied to at least one tube had a probability of failure (38.0 per 1000 procedures; 95% CI 19.1, 57.0) similar to that in which only one clip was applied to both tubes (35.4 per 1000 procedures; 95% CI 22.2, 48.7; P = .82).

As with the silicone rubber band, the 10-year cumulative probability of pregnancy varied widely by study site. The highest cumulative probability (78.0 per 1000 procedures at 5 years; 95% CI 47.2, 108.8) was more than ten times the lowest cumulative probability (7.1 per 1000 procedures at 10 years; 95% CI 0.0, 15.1; P < .001).

We analyzed 12 factors to determine their impact on the relative risk of failure of spring clip application: age at sterilization, race or ethnicity, study site, education, marital status, gravidity, history of PID, history of abdominal or pelvic surgery, type of anesthesia, presence of adhesions recorded at sterilization, tubal disease recorded at sterilization, and whether the clip was applied solely to the proximal third of both fallopian tubes. We found that race or ethnicity, study site, history of abdominal or pelvic surgery, and tubal disease reported at sterilization were significant by multivariable analysis (Table 2). Procedures in which a clip was applied to other than the proximal third of either tube were more likely to fail (relative risk [RR] 1.7; 95% CI 0.9, 3.1), although that increase was marginally statistically significant (one-tailed P = .04). When we restricted the analysis to the three sites that enrolled participants in both 1979–1983 and 1985–1987, women enrolled in the early period were more likely to become pregnant, although that difference was not significant (RR 1.9; 95% CI 0.5, 6.9; P = .28).

	Discussion

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The silicone rubber band and the spring clip were developed in the early 1970s as alternatives to unipolar electrocoagulation for laparoscopic sterilization. We reported previously³ that all the laparoscopic methods are highly effective; the overall 10-year cumulative probabilities of failure range from approximately 1% to 4%, depending on the method. In this analysis, we found that proper placement of the silicone rubber band or spring clip is a key determinant of success.

The silicone rubber band, developed by Yoon et al,⁶ should be applied to a loop of the fallopian tube created by grasping the isthmic portion of the tube, about 3 cm from the uterus.^6,7 Although such an application may include the ampullary portion of the tube, application to the distal third of the tube should be avoided. The spring clip, developed by Hulka et al,⁸ should be applied to the isthmic portion of the tube, approximately 2 cm from the uterus, after the tube is placed on stretch. It is important that the clip be applied perpendicular to the long axis of the tube.^7,8

We found that the effectiveness of spring clips, like bipolar coagulation,⁴ is influenced by whether the tube is anatomically normal. In particular, women were at increased risk of pregnancy after clip application if they had tubal disease recorded at sterilization. It is likely that surgeons find it more difficult to place diseased tubes on stretch and to ensure proper placement of clips on diseased tubes. Our analysis may underestimate the effect of severe tubal disease on the risk of pregnancy, for at least two reasons. First, women with severe tubal disease may not be considered appropriate candidates for occlusion by bands or clips, and another surgical approach may be used instead. Second, if band or clip application was attempted but was unsuccessful on at least one tube, the procedure was excluded from our analysis, which was restricted to procedures in which bands or clips were applied to both tubes. Thus, the participants in our analysis were more likely to have had mild than severe tubal disease. Race or ethnicity, which influenced the effectiveness of spring clips, may have served as a marker for other determinants of risk—including tubal disease—which may have been incompletely reported.

We previously detailed the strengths and weaknesses of the US Collaborative Review of Sterilization for estimating the effectiveness of tubal sterilization.^3,5 Although relatively large numbers of women who underwent procedures with silicone rubber bands or spring clips were studied, there was low statistical power to detect genuine differences in some key subgroup analyses. Most women in this study were enrolled in teaching institutions, and the extent to which the findings on pregnancy rates can be generalized outside of such settings is unclear. Further, although the nearly two-fold higher risk of pregnancy among women undergoing clip sterilization early in the study was non-significant, we found in another study⁴ that women undergoing bipolar coagulation early in the study were significantly more likely to become pregnant. The study began shortly after bipolar coagulation and clip and band application became available; pregnancy rates after these methods may have decreased with experience over time.

The site-specific 10-year cumulative probabilities of pregnancy ranged from 0.0 to 42.5 per 1000 silicone rubber band applications and from 7.1 (at 10 years) to 78.0 (at 5 years) per 1000 spring clip applications. These findings lead to two important observations. 1) The long-term failure rates for silicone rubber band and spring clip applications can be less than 1%; thus, these methods can be as effective as other laparoscopic methods. 2) The wide variation in failure rates by study site is greater than the variability in rates for bipolar coagulation.⁴ The highest (10-year) probability of 42.5 pregnancies per 1000 silicone rubber band applications was from four combined sites that each performed fewer than 100 silicone rubber band applications, and the highest (5-year) probability of 78.0 pregnancies per 1000 spring clip applications came from a single site with relatively little experience with the method. One site, consisting primarily of the private practice of a single surgeon with substantial experience in both methods, had one of the lowest failure rates for silicone rubber band application (2.9 pregnancies per 1000 procedures at 10 years) and the lowest failure rate for spring clip application (7.1 pregnancies per 1000 procedures). These observations highlight the importance of technical expertise and proper application for both methods.

	Footnotes

 
The US Collaborative Review of Sterilization Working Group, Design, Coordination, and Analysis Center, Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia: Norman G. Courey, MD, CM, State University of New York at Buffalo, Erie County Medical Center, Buffalo, New York; Philip D. Darney, MD, MSc, University of California, San Francisco, San Francisco, California; Ernst R. Friedrich, MD, Washington University School of Medicine, St. Louis, Missouri; Ralph W. Hale, MD, and Roy T. Nakayama, MD, Kapiolani Medical Center, Honolulu, Hawaii; Jaroslav F. Hulka, MD, University of North Carolina School of Medicine, Chapel Hill, North Carolina; Alfred N. Poindexter, MD, Baylor College of Medicine, Houston, Texas; George M. Ryan, MD, and Edwin M. Thorpe, MD. University of Tennessee School of Medicine, Memphis, Tennessee; Gary K. Stewart, MD (deceased), Planned Parenthood of Sacramento, Sacramento, California; and Howard A. Zacur, MD, and Lucas Blanco, MD, Johns Hopkins University School of Medicine, Baltimore, Maryland.

Supported by an interagency agreement (3-Y02-HD41075-10) with the National Institute of Child Health and Human Development.

PII S0029-7844(00)01114-5

Received February 16, 2000. Received in revised form August 29, 2000. Accepted October 5, 2000.

	References

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1. Piccinino LJ, Mosher WD. Trends in contraceptive use in the United States: 1982–1995. Fam Plann Perspect 1998;30:4–10, 46.

2. Peterson HB, Hulka JF, Phillips JM, Surrey MW. Laparoscopic sterilization: American Association of Gynecologic Laparoscopists’ 1991 membership survey. J Reprod Med 1993;38:572–3.[Medline]

3. Peterson HB, Xia Z, Hughes JM, Wilcox LS, Tylor LR, Trussell J, for the U.S. Collaborative Review of Sterilization Working Group. The risk of pregnancy after tubal sterilization: Findings from the U.S. Collaborative Review of Sterilization. Am J Obstet Gynecol 1996; 174:1161–70.[Medline]

4. Peterson HB, Xia J, Wilcox LS, Tylor LR, Trussell J, for the U.S. Collaborative Review of Sterilization Working Group. Pregnancy after tubal sterilization with bipolar electrocoagulation. Obstet Gynecol 1999;94:163–7.[Abstract/Free Full Text]

5. Peterson HB, Xia Z, Hughes JM, Wilcox LS, Tylor LR, Trussell J, for the U.S. Collaborative Review of Sterilization Working Group. The risk of ectopic pregnancy after tubal sterilization. N Engl J Med 1997;336:762–7.[Abstract/Free Full Text]

6. Yoon IB, Wheeless CR Jr, King TM. A preliminary report on a new laparoscopic sterilization approach: The silicone rubber band technique. Am J Obstet Gynecol 1974;120:132–6.[Medline]

7. Hulka JF, Reich H. Textbook of laparoscopy. 2nd ed. Philadelphia: WB Saunders, 1994:129–51.

8. Hulka JF, Fishburne JI, Mercer JP, Omran KF. Laparoscopic sterilization with a spring clip: A report of the first 50 cases. Am J Obstet Gynecol 1973;116:715–8.[Medline]

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