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Unplanned pregnancies after having your 'tubes tied' may be "considerably more common than many expect," according to a new analysis based on nationally representative data in the United States.
The research, led by scientists at the University of California, San Francisco, has found that accidental pregnancy can occur in more than 5 percent of people after tubal sterilization – which involves cutting, clamping, blocking, or removing the fallopian tubes.
By contrast, an intrauterine device or a contraceptive implant is more than 99 percent effective.
Given how many women in the US express interest in permanent contraception, researchers argue we need to properly evaluate the real-world effectiveness of all forms of tubal sterilization. Especially since getting pregnant after one of these procedures increases the risk of ectopic pregnancy, where a fertilized egg attaches and grows outside the uterus in a way that is ultimately nonviable and can threaten the health of the mother.
"This study shows that tubal surgery cannot be considered the best way to prevent pregnancy," concludes general internist Eleanor Schwarz from the University of California San Francisco (UCSF).
"People using a contraceptive arm implant or an IUD are less likely to become pregnant than those who have their tubes tied."
Tubal sterilization is one of the most common routes for permanent birth control in the US, with more than 20 percent of women in their 30s undergoing these procedures and nearly 40 percent of women in their 40s.
Patients are often assured they no longer need to use additional forms of birth control. In 2019, a woman who got pregnant after both her fallopian tubes were removed said that she had been told the surgery was "as close to 100 percent as you can get."
Depending on what procedure is done and how it is done, however, tubal sterilization may not put a permanent end to a person's fertility.
Currently, the American College of Obstetricians and Gynecologists (ACOG) reports that the rate of pregnancy after female sterilization is about one percent over five years. But this number is based on a study that began in 1978 and closed in 1986.
The new data was collected from over 4,000 Americans, between the ages of 15 and 44, who had tied their tubes between 2013 and 2015.
Schwarz and her team from UCSF, Johns Hopkins University, Cornell University, and the University of California, Davis found nearly 3 percent of their cohort fell pregnant within a year of having their procedure.
Ten years after tubal sterilization, the rate of pregnancy was 8.4 percent.
The findings agree with a recent analysis from the state of California, which found that more than 2 percent of patients who had a tubal sterilization procedure experienced a pregnancy within a year, and more than 6 percent experienced a pregnancy within five years.
Since the 1980s, when studies first analyzed the failure rates of tubal sterilization, the surgical landscape in the US has changed dramatically.
First, Schwarz and her colleagues explain, there was the introduction of hysteroscopic sterilization – which involves inserting a coil into the fallopian tubes to block an egg and sperm from meeting – and then there came increased rates of salpingectomy – which removes the tubes entirely.
The safety of inserting devices into the fallopian tubes has been seriously questioned in recent years, with the most popular device being discontinued as of 2020, after it resulted in more than 4,000 pregnancies in patients from 2002 onward.
Today, a bilateral salpingectomy is often considered the most effective form of tubal sterilization, but with little data on hand, the failure rate of this newer procedure is currently unknown.
The first ever documented case of a woman getting pregnant after a double salpingectomy was reported in 2005. A second case was not published for three more years.
An egg traveling through the space between the ovary and the uterus is often considered rare; however, when a remnant of the tube is left in place, case studies suggest it can increase the risk of an unplanned pregnancy.
"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," explains Schwarz.
"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."
Researchers are now keen to investigate how different methods of tubal sterilization compare with one another when it comes to real-world failure rates.
"Our findings highlight the need for ongoing monitoring of the effectiveness of permanent contraceptive procedures," the authors conclude.
The study was published in NEJM Evidence.
