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Rates of pregnancy after tubal sterilization may be higher than previously expected, according to an analysis of national survey data.

After having their "tubes tied," 2.9% to 5.2% of women later reported becoming pregnant across four different waves of the survey, Eleanor Schwarz, MD, of the University of California San Francisco, and colleagues .

In the most recent survey wave (2013-2015), failure at 1 year was estimated to be 2.9%, while failure at 10 years was 8.4%, the researchers found.

"Because the Dobbs decision has further limited access to pregnancy termination services for many U.S. women, information on contraceptive effectiveness is particularly salient," the researchers wrote.

Schwarz told MedPage Today that the study provides more clarity on the procedure's real-world effectiveness.

"Women considering tubal surgery should be well-informed about options that can be safely and conveniently used for years and are likely to be more effective -- including the arm implant, hormonal IUD [intrauterine device], hormone-free IUD, and vasectomy," she said.

After meeting a number of women who had become pregnant following tubal sterilization, Schwarz said she started to wonder how often it actually occurs. The American College of Obstetricians and Gynecologists estimates that 18 to 37 of every 1,000 women still get pregnant within 10 years of having a laparoscopic sterilization surgery, but Schwarz said it seemed more common based on her observations.

She and her colleagues analyzed data on women ages 15-44 from the National Survey of Family Growth (NSFG), a periodic nationally representative survey that provides estimates of factors affecting pregnancy and birth outcomes, such as sexual activity and contraceptive use. They looked at four waves (2002, 2006-2010, 2011-2013, and 2013-2015), identified women who had a tubal sterilization, and calculated the number of months that had passed between the surgery and pregnancy.

The majority of tubal sterilizations occurred postpartum and more than half of the women had the procedure before age 35. Most of the pregnancies were intrauterine, though between 12.1% and 32.6% were ectopic.

Schwarz and colleagues found in unadjusted analyses that contraceptive failure was less common following postpartum procedures than after interval procedures, but those differences disappeared in multivariable analyses.

Age at the time of tubal ligation remained a predictor of pregnancy in those multivariable analyses, with older women being considerably less likely to become pregnant after the procedure, they reported.

Funding of tubal sterilizations by Medicaid wasn't associated with a greater likelihood of pregnancy compared with private or other insurance, they added. Nor was pregnancy after tubal sterilization associated with race/ethnicity, educational attainment, or living in a metropolitan area.

In an , Julia Tasset, MD, MPH, and Maria Rodriguez, MD, MPH, both from the Oregon Health & Science University in Portland, wrote that the study was "one of the first attempts to update clinical understanding of the effectiveness of permanent tubal contraceptive procedures in the era of modern laparoscopy."

Most knowledge about tubal sterilization is based on 40-year-old data from the pivotal CREST (Collaborative Review of Sterilization) study, they wrote. Schwarz and team's estimates of pregnancy after tubal sterilization "are four to five times higher than estimates given in the CREST study and are higher than the typical-use risk of failure for long-acting reversible contraceptive methods, such as the intrauterine device or subdermal implant," they wrote.

They also noted that these results "are surprising not only for the magnitude of difference but also in light of the shift toward interval laparoscopic permanent tubal contraception."

In a , Hyungjin Myra Kim, ScD, of the University of Michigan in Ann Arbor, commended the authors on their study design, which can be tricky when analyzing outside survey data.

The authors "designed their study to utilize existing survey data effectively" and "demonstrated the value of secondary data analysis based on the nationally representative survey data by careful decision-making regarding data management methodology, enabling them to derive meaningful conclusions," Kim wrote.

Schwarz and colleagues noted a handful of limitations, including that NSFG relies on participant recall and doesn't distinguish between the types of laparoscopic sterilization procedures. It also does not distinguish between hysteroscopic and laparoscopic sterilization procedures, though previous research found similar rates of effectiveness between approaches. Additionally, some participants may not have reported pursuing assisted fertility services and NSFG data are known to underreport abortions. Also, the authors conservatively excluded the small number of women with imputed dates of conception.