Pregnancy after sterilization turns out to be surprisingly common

Tubal sterilization is thought to be a permanent form of birth control and is the most common method of contraception nationally. But a new study led by UC San Francisco reports that tubal surgery fails often enough that some other forms of birth control are usually more effective.

The authors found that 3–5% of women in the United States who had their tubes tied later reported an unplanned pregnancy. This failure rate led the authors to suggest that patients who really want to avoid future pregnancy should instead use a contraceptive arm implant or intrauterine device (IUD).

The paper appears August 27 in NEJM Evidence.

Interest in permanent contraception has risen since the 2022 U.S. Supreme Court Dobbs decision removed federal protections for abortion services and limited access to abortion services in many states. As a result, the researchers say that information about contraceptive effectiveness is especially important.

"Since the Dobbs decision, many more people are worried about how pregnancy may impact their health and family life," said first author Eleanor Bimla Schwarz, MD, chief of the UCSF Division of General Internal Medicine at Zuckerberg San Francisco General. "This is especially true for patients with medical conditions like diabetes and high blood pressure that can complicate pregnancy.

"This study shows that tubal surgery cannot be considered the best way to prevent pregnancy," Schwarz said. "People using a contraceptive arm implant or an IUD are less likely to become pregnant than those who have their tubes tied."

Many U.S. women get tubal surgeries

About 65% of women 15 to 49 in the U.S. use birth control, according to national statistics, and tubal sterilization—an abdominal surgery in which the fallopian tubes are clamped or cut and removed—is used by more than 21% of women ages 30 to 39, and 39% of women older than 40. These surgeries are especially common among low-income people and those with chronic medical conditions.

Tubal sterilization aims to permanently end fertility, but as previously reported, women can nonetheless get pregnant. Based on older studies, the American College of Obstetricians and Gynecologists has advised that fewer than 1% of patients become pregnant after tubal sterilization.

In the new study, the authors examined four independent rounds of the National Survey of Family Growth from 2002 to 2015. Data were collected from more than 31,000 women, including 4,184 who reported having undergone tubal sterilization and were the focus of the study.

Within the first year after tubal surgery, the researchers estimated that 2.9% of those who reported having been sterilized in 2013 to 2015 became pregnant. The chance of pregnancy was highest among those who were younger at the time of their tubal surgery.

Patients who had Medicaid-funded procedures were not more likely than those with private insurance to become pregnant. In recent years, the proportion of respondents who reported a tubal sterilization funded by Medicaid has increased from 18% in 2002 to about 36% from 2013 to 2015.

"When choosing what birth control will work best for them, people consider many different things including safety, convenience and how fast they can start to use the method," Schwarz said. "For people who have chosen a 'permanent' method, learning they got pregnant can be very distressing. It turns out this is unfortunately a fairly common experience."

Besides Schwarz, authors are Amy Yunyu Ciang, Ph.D., of UCSF; Carrie A. Lewis, MPH, of the Center for Healthcare Policy and Research at UC Davis; Aileen M. Gariepy, MD, of Weill Cornell Medicine at Cornell University; and Matt Reeves, MD, of the Bloomberg School of Public Health at Johns Hopkins University.