“The Risk of Ectopic Pregnancy after Tubal Sterilization” (1997), by Herbert B. Peterson, Zhisen Xia, Joyce M. Hughes, Lynne S. Wilcox, Lisa Ratliff Tylor, and James Trussell

By: Cole Nichols

Published: 2025-06-05

In 1997, Herbert B. Peterson and colleagues published “The Risk of Ectopic Pregnancy after Tubal Sterilization,” hereafter “The Risk of Ectopic Pregnancy,” in The New England Journal of Medicine. The article contains the authors’ reports on the United States Collaborative Review of Sterilization, a multi-hospital study the authors performed from 1978 through 1994 that involved over 10,000 patients from across the United States undergoing tubal sterilization, a common method of permanent contraception for people with female reproductive systems. “The Risk of Ectopic Pregnancy” reveals that bipolar coagulation, one of the methods of tubal sterilization, is associated with a higher risk of an ectopic pregnancy, a life-threatening pregnancy complication, after sterilization. “The Risk of Ectopic Pregnancy” was an early study into the possible complications from tubal sterilization, and its authors reveal the risk of a serious health consequence associated with a popular method of contraception.

Author Information

Most of the authors of “The Risk of Ectopic Pregnancy” worked for the Centers for Disease Control and Prevention, or CDC, as well as various academic medical centers in the United States at the time of the study. During the study, Peterson, the first-listed author, worked as a public health researcher and branch chief of the Women’s Health and Fertility at the National Center for Chronic Disease Prevention and Health Promotion. As of 2025, Peterson teaches at the Gillings School of Global Public Health and the Department of Obstetrics and Gynecology at the University of North Carolina in Chapel Hill, North Carolina. He also works as the director of the World Health Organization, or WHO, Collaborating Center for Research Evidence for Sexual and Reproductive Health, which the Gillings School at Chapel Hill houses. James Trussell, one of the authors, worked with the Office of Population Research at Princeton University in Princeton, New Jersey. All other researchers worked with the Division of Reproductive Health at the CDC.

Defining Ectopic Pregnancy and Tubal Sterilization

In “The Risk of Ectopic Pregnancy,” the researchers report on data concerned with surgeries involving the fallopian tubes and possible subsequent health complications. In the female reproductive system, one fallopian tube extends from each of the two ovaries to each side of the uterus. During ovulation, an egg cell moves from the ovary into the fallopian tube. The tube is also the site of fertilization, in which an egg cell and sperm cell fuse to form a zygote, which may lead to a pregnancy. A possible pregnancy complication involving the fallopian tubes is an ectopic pregnancy. An ectopic pregnancy occurs when the zygote implants anywhere other than the uterus. Often, ectopic pregnancies involve a zygote implanting into the fallopian tube, but some can involve implantation into the ovary or other nearby areas. Structures other than the uterus cannot support embryonic development or physically hold the growing embryo. Consequently, ectopic pregnancies pose serious health risks, and people are likely to develop severe internal bleeding if such a pregnancy ruptures.

The fallopian tubes’ role in reproduction has led to them being a focus of sterilization surgeries for people with female reproductive systems. Surgically interfering with the fallopian tubes’ ability to transport an egg from the ovary leads to infertility. People choose to undergo the surgery as a form of birth control. Surgeons typically access the fallopian tubes via laparoscopy or laparotomy. In a laparoscopic procedure, a surgeon makes a small incision in the abdomen, through which they can pass surgical equipment to perform a procedure. A laparotomy requires a larger incision in the abdomen to open the abdominal cavity rather than insert equipment into it. Salpingectomy and electrical coagulation are common methods to block the passage of an egg through the fallopian tubes. A salpingectomy is the removal of a portion or all of the fallopian tube through tying off or clamping it. In electrical coagulation, a surgeon burns the tubes’ tissue and seals them with an electrical current. Electrical coagulation can be bipolar, where the electrical current passes through two ends of forceps grabbing the tube, or unipolar, where only one end of the forceps carries the electrical current. In unipolar coagulation, the electrical current moves through the body to a metal plate underneath.

Context and Overview of the Study

“The Risk of Ectopic Pregnancy” emerged from a set of studies on sterilization and its effects from a research project called the US Collaborative Review of Sterilization, or CREST. The authors of “The Risk of Ectopic Pregnancy” report that, by 1990, tubal sterilization had become one of the most common methods of birth control for people with female reproductive systems. The authors of “The Risk of Ectopic Pregnancy” argue that, by the 1970s and 1980s, there had not been enough large-scale evaluations of the effectiveness or safety of tubal sterilization procedures. The authors and a number of other researchers in reproductive healthcare began CREST in 1978 to begin such research. CREST also received sponsorship and direction from the CDC and the National Institute for Child Health and Human Development, or NICHD. The project’s researchers focused on people undergoing tubal sterilization in academic medical centers in Buffalo, New York; Honolulu, Hawaii; and Houston, Texas, among other cities across the United States. The group enrolled participants in studies on tubal sterilization between 1978 and 1986. The data collection for “The Risk of Ectopic Pregnancy” continued until 1994, as the researchers continued following up with participants. Multiple publications came from the work of CREST. The studies primarily contain analyses of the outcomes and potential complications of female sterilization procedures as well as some work on male sterilization.

“The Risk of Ectopic Pregnancy” has four sections. In the untitled introduction, Peterson and colleagues justify their study by stating that tubal sterilization was, at the time, the most popular method of birth control for women in the United States. They also state that researchers knew too little about the associated risks of ectopic pregnancy. In the “Methods” section, the authors outline the structure of the CREST project, the sterilization methods they investigated, and the series of initial and follow-up interviews they performed. In “Results,” the researchers indicate that certain methods and factors had higher rates of subsequent ectopic pregnancy, including bipolar coagulation and being younger than thirty years old. In “Discussion,” the authors comment on what they find as a substantial risk of ectopic pregnancy after tubal sterilization. They also discuss potential limitations to the study and caution against taking the results out of context when making decisions about sterilization.

“The Risk of Ectopic Pregnancy,” Section by Section

In the unnamed introduction, the authors explain that, despite the popularity of tubal sterilization at the time, few researchers had studied the procedure’s potential consequences. The authors cite that, as of the time of publication, over ten million women in the United States had undergone tubal sterilization procedures. They go on to report that, as of 1990, women had received tubal sterilization procedures more than any other method of birth control. Though pregnancies after sterilization are uncommon, the authors report that there is a risk of post-sterilization pregnancies being ectopic. According to the authors, outside of the context of sterilization, ectopic pregnancies are involved in nine percent of all pregnancy-related deaths. Additionally, Peterson and colleagues explain that at the time of publication, information regarding the chances of pregnancy after sterilization was limited. Researchers had not been able to give an accurate assessment of the risk of ectopic pregnancy after tubal sterilization.

The authors continue the introduction with a brief description of the research project that led to “The Risk of Ectopic Pregnancy.” They introduce their research project, CREST, which began in 1978 to assess the long-term effects of tubal sterilization procedures and focused on safety and efficacy. The authors report that, from a separate article on sterilization failure they published in 1996, the project had originally found a cumulative probability of 18.5 pregnancies per 1,000 sterilizations ten years after each procedure. The authors then indicate that “The Risk of Ectopic Pregnancy” involves the same group of participants. For “The Risk of Ectopic Pregnancy,” the authors focus the article on outcomes related to ectopic pregnancy rather than only sterilization failure.

Next, Peterson and colleagues begin “Methods” by describing the participants and timeline of their study. CREST researchers enrolled participants between 1978 and 1986, following up with them after their procedures until 1994, to obtain a dataset that researchers could analyze differently for multiple separate studies, including “The Risk of Ectopic Pregnancy.” The participants underwent their sterilization procedures at medical centers in nine cities across the United States. The authors state that the participants were between the ages of eighteen and forty-four years old. They also state that a trained nurse-interviewer took a detailed medical history from each participant. The nurse-interviewer also recorded details about the sterilization procedure itself, such as the occurrence of any complications. The researchers reported that they contacted the participants for follow-up beginning one month after their procedures via telephone and continued to contact them annually for five years. The participants who enrolled between 1978 and 1983 received final follow-up interviews between eight and fourteen years after their sterilization procedures.

Continuing the “Methods” section, the authors describe what data they collected from the participants. In the follow-up interviews, the researchers attempted to find whether any of the participants had become pregnant after their sterilizations. They tried to gather all details related to the pregnancy along with any pertinent medical records. The authors discuss dividing the causes of the pregnancies into two categories. They did not classify the pregnancy as a failure of sterilization if they had reason to suspect the participant was pregnant before their sterilization and did not find out until afterward. The researchers classified it as a failure of sterilization if they thought the pregnancy occurred after the sterilization. The authors state that they classified all uncertain cases as failures of sterilization, which they admit could lead to an underestimation of the sterilization failure rate.

The authors continue “Methods” with a discussion of how they decided to remove participants from the study. They report that they stopped continuing to follow up with a participant if any one of five things happened at any point after sterilization. The five criteria for exclusion from further follow-up were the participant dying, becoming pregnant, undergoing a sterilization reversal procedure, undergoing a second sterilization procedure, or undergoing a hysterectomy. A hysterectomy is a procedure in which a surgeon removes some combination of the uterus, fallopian tubes, and/or ovaries from a person’s body. The researchers also excluded any participants with whom they lost contact and those who declined interviews.

Peterson and colleagues follow their criteria for excluding certain participants with the factors that allowed participants to initially enroll in the study. For inclusion in the study, the participants had to have received the same method of sterilization on both of their fallopian tubes. The methods of sterilization included four laparoscopic methods and one method by laparotomy. The laparoscopic sterilization methods that the authors considered included bipolar and unipolar electrical coagulation, one method in which a small rubber band closes off the tubes and one in which a spring clip closes off the tubes. The method via laparotomy the authors included was a partial or total removal of the fallopian tubes. For the partial removal method, the authors divided participants based on whether the removal happened right after giving birth or not. The authors end “Methods” by stating that any pregnancies they recorded as failures of sterilization received further classification as either happening inside the uterus or ectopic.

The researchers begin the “Results” section with information regarding their ability to retain participants in the study. The authors report that they enrolled 10,863 participants in the study and excluded 178 of them for the reasons they outlined in “Methods.” The authors then report that they were able to successfully follow up with 10,685 participants over the years. According to the researchers, 89.2 percent of them were available for follow-up after one year, eighty-one percent were available after three years, and seventy-three percent were available after five years. At the final interval of eight to fourteen years, 57.7 percent were available for follow-up. The authors state that 217 participants, or two percent, declined to continue giving them information at follow-up.

The authors continue “Results” by discussing the demographics and pregnancy outcomes of the participants. The authors state that the participants’ median age was thirty years, that most of them were White, and nearly ninety percent of them had been pregnant at least twice before the study. Of the pregnancies that were true failures of sterilization, the authors report that 32.9 percent of them were ectopic. Most of the ectopic pregnancies were tubal pregnancies, with the embryo residing in the fallopian tubes. The researchers report that the cumulative probability of ectopic pregnancy at ten years after tubal sterilization was 7.3 per 1,000 procedures. The authors state that the probability of ectopic pregnancy varied with two factors: the method of sterilization and the participant’s age. Bipolar coagulation had the highest probability of ectopic pregnancy after sterilization. Fallopian tube removal after giving birth had the lowest probability of failure. Generally, participants sterilized under the age of thirty years had a higher ten-year probability of ectopic pregnancy. The authors specify that for that group younger than thirty years old, bipolar coagulation was the method with the highest probability of pregnancy, which was 31.9 per 1,000 procedures. For participants who were older than thirty years old by the time of sterilization, there were no significant differences in the probability of pregnancy across sterilization methods.

The authors end “Results” by discussing the effects of the sterilization method and identifying risk factors for ectopic pregnancy after sterilization, such as age, ethnicity, sterilization method, and medical history. The researchers report that bipolar coagulation had the highest rate of failure, meaning the highest rate of pregnancies after sterilization. That method also had the highest proportion of ectopic pregnancies out of all the pregnancies the failure caused. The lowest proportion of ectopic pregnancies among all pregnancies occurred with laparoscopic spring clip application. For all sterilization methods, the authors state that the proportion of ectopic pregnancies was three times higher in the fourth through tenth years after sterilization than in the first three years. The authors identified ten potential risk factors for ectopic pregnancy following tubal sterilization. Of those ten, the authors reported that four of them had a statistically significant relationship with ectopic pregnancy risk, which were sterilization method, age when sterilization occurred, ethnic group, and history of pelvic inflammatory disease, or PID. PID is a serious infection of the female reproductive tract that often comes from infection with sexually transmitted infections, or STIs. The participants with the highest risk of ectopic pregnancy were patients who underwent bipolar coagulation, patients younger than thirty years old, Black patients, and patients who had previously had PID.

In the “Discussion” section, the authors explore potential reasons why ectopic pregnancy was a higher risk for people younger than thirty years old and discuss the possible consequences of losing contact with Black participants during follow-up. The authors then argue that the difference between participants under the age of thirty years old and over the age of thirty years old is likely due to higher fecundity, or ability to become pregnant, in younger participants. Regarding the possibility of bias in their analysis, the researchers reveal they lost contact with more young and Black participants during follow-up and that those groups had generally higher rates of ectopic pregnancy. The authors propose that the loss of some of those participants would lead to an overall underestimation of ectopic pregnancy risks if those participants with whom they lost contact also had higher rates of ectopic pregnancy. Additionally, the authors recognize that they cannot generalize statistics to the entirety of the United States because they mostly enrolled people at academic medical centers and that the rates of ectopic pregnancy could differ had they enrolled participants from other institutions.

Also, in the “Discussion” section, Peterson and colleagues discuss possible limitations of their study’s conclusions and acknowledge the potential risks of tubal sterilization, but they urge others not to consider the procedure overly risky based on their study alone. They primarily argue that the prevalence of sterilization failure and subsequent ectopic pregnancy for bipolar coagulation was probably due to improper technique during the procedure. The authors concede that they could have overestimated the risks of sterilization failure and ectopic pregnancy if the proper technique had become more widespread after they had finished enrolling participants. The researchers also state that bipolar coagulation having a significantly higher risk of ectopic pregnancy was notable. That method is popular for people who have not recently given birth. Adding nuance to their conclusions, Peterson and colleagues state that people should not view the risks of ectopic pregnancy in isolation. They include the example that physicians generally consider it to be a safer procedure than unipolar coagulation, even though bipolar coagulation had the highest risk of ectopic pregnancy. The researchers end the article by stating that ectopic pregnancy after tubal sterilization is not a rare occurrence and that people who have undergone tubal sterilization should not dismiss the risk of ectopic pregnancy.

Impacts

As of 2025, more than 290 research articles have cited “The Risk of Ectopic Pregnancy.” Such articles include analyses of overall risks and treatment considerations for ectopic pregnancy, pieces on the possible complications and risks associated with tubal sterilization surgeries, and studies comparing the benefits and risks of various methods of tubal sterilization. A 2014 observational study found an increased risk of ectopic pregnancies for women sterilized before the age of twenty-eight years and for women sterilized using the laparoscopic partial salpingectomy method. Another publication in the Journal of Women’s Health from 2017 cites “The Risk of Ectopic Pregnancy” to show the risk of ectopic pregnancy and discuss the relationship between domestic violence and voluntary sterilization. That publication concluded that intimate partner violence, or IPV, was linked to a higher rate of sterilization surgeries among affected women. The 2019 practice bulletin from the American College of Obstetricians and Gynecologists, or ACOG, titled “Benefits and Risks of Sterilization” cites “The Risk of Ectopic Pregnancy” in its guidance for physicians on the potential risk of sterilization surgeries.

After the publication of “The Risk of Ectopic Pregnancy,” CREST continued publishing studies on various topics related to sterilization. Many of the authors from “The Risk of Ectopic Pregnancy” continued to work together and focused on the risks of ectopic pregnancies. Further studies from CREST published in the late 1990s and early 2000s involved surveying participants to study those who regretted their sterilization procedures, the factors in seeking sterilization reversal, and possible effects on menstrual and sexual function after sterilization procedures. Some studies from CREST in the early 2000s involve pregnancy risk after vasectomy, which is a common sterilization surgery for people with male reproductive systems.

“The Risk of Ectopic Pregnancy” was one of the first articles reporting on a large-scale study of people who had undergone tubal sterilization to measure their risk for ectopic pregnancy. Finding that ectopic pregnancy was still a health risk after tubal sterilization, the article’s authors contributed new insight to the understanding of the effects of a common form of birth control.

Sources

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