Tubal Sterilisation May Be Less Effective Than Expected

Tubal sterilisation and the risk of pregnancy

A new analysis using nationally representative United States data suggests that unplanned pregnancies following a ‘tubes tied’ procedure may be “considerably more common than many expect”.

The study, headed by researchers at the University of California, San Francisco, found that more than 5 percent of people may experience an unintended pregnancy after tubal sterilisation. The procedures can involve cutting, clamping, blocking or removing the fallopian tubes.

In comparison, both an intrauterine device (IUD) and a contraceptive implant are more than 99 percent effective.

As many women in the US are interested in permanent contraception, the researchers say the real-world effectiveness of every type of tubal sterilisation needs to be assessed carefully. This is particularly important because pregnancy after such a procedure carries a higher risk of ectopic pregnancy. In these pregnancies, a fertilised egg implants and develops outside the uterus; it cannot survive and may endanger the mother’s health.

“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.”

Pregnancy rates after tubal sterilisation

Tubal sterilisation is among the most widely used methods of permanent birth control in the US. More than 20 percent of women in their 30s have these procedures, as do nearly 40 percent of women in their 40s.

Patients are commonly told that they will not need to use another form of contraception afterwards. In 2019, a woman who became pregnant despite having both fallopian tubes removed said she had been told that the operation was “as close to 100 percent as you can get.”

Yet a tubal sterilisation procedure may not permanently end someone’s fertility, depending on both the type of operation performed and how it is carried out.

At present, the American College of Obstetricians and Gynecologists (ACOG) puts the pregnancy rate after female sterilisation at roughly one percent over five years. However, that estimate comes from a study that started in 1978 and ended in 1986.

The new research drew on data from more than 4,000 Americans aged 15 to 44 who had their tubes tied between 2013 and 2015.

Schwarz and colleagues from UCSF, Johns Hopkins University, Cornell University and the University of California, Davis found that nearly 3 percent of the study group became pregnant within one year of their procedure.

After ten years, the pregnancy rate following tubal sterilisation was 8.4 percent.

These results align with a recent California state analysis. It reported that more than 2 percent of patients who underwent a tubal sterilisation procedure had a pregnancy within one year, while more than 6 percent did so within five years.

Changing procedures and uncertain failure rates

The US surgical landscape has altered substantially since the 1980s, when tubal sterilisation failure rates were first studied.

As Schwarz and her co-authors note, hysteroscopic sterilisation was first introduced. This technique involves placing a coil in the fallopian tubes to prevent an egg and sperm from meeting. Rates of salpingectomy, which removes the tubes altogether, then increased.

In recent years, serious concerns have been raised about the safety of placing devices in the fallopian tubes. The most popular device was withdrawn in 2020 after causing more than 4,000 pregnancies in patients from 2002 onwards.

A bilateral salpingectomy is now frequently regarded as the most effective type of tubal sterilisation. However, because little evidence is available, the failure rate for this more recent procedure remains unknown.

The first documented pregnancy after a double salpingectomy was reported in 2005, with a second case not published until three years later.

While an egg moving through the gap between the ovary and uterus is generally thought to be uncommon, case studies indicate that leaving a portion of the tube in place may raise the likelihood 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 now want to examine how the real-world failure rates of the various tubal sterilisation methods compare.

“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.