Women who receive Bayer's female sterilization implant are about 10 times as likely to have to go through a second sterilization procedure due to complications, compared with women who opt for surgery.

The finding, published today in the BMJ, adds to mounting concerns over the safety of the sterilization implant called "Essure." That said, the risks of reoperation is still low — at 2.4 percent — so the researchers who conducted the study aren't calling for a device recall. At least not yet.

This study could have an impact of the FDA's eventual decision

Female sterilization, which is permanent, can be a big help for women who don't want children anymore. For decades, the main method for sterilizing women has been abdominal surgery to block the fallopian tubes. That method involves anesthesia. But in 2002, the US Food and Drug Administration approved another option: the Essure device, which enables implant-based female sterilization.

Sold by Bayer, Essure works by causing scar tissue to grow around the implant, thus blocking the fallopian tubes. (A second device, approved in 2009 and called Adiana, worked similarly but it was removed from the market in 2012.) The main advantage of this method is that, unlike surgery, the procedure doesn't require general anesthesia. But complaints from women have lead to calls for its removal from the market. The device, some womensay, causes pain, allergic reactions, and bleeding — among other things. As a result, the FDA held a hearing in September to discuss the device's safety. That's why this new study is so important. Until now, a comparison of the different outcomes that women experience with the Essure device and with surgery hadn't been completed. So, the findings of this study could have an impact of the FDA's eventual decision.

In the study, researchers analyzed data from 8,000 women who received the implant and 44,000 who underwent surgical sterilization in New York State between 2005 and 2013. After adjusting the data to account for various patients characteristics — like age and health — the researchers found that women who undergo implant-based female sterilization had a 10-fold higher risk of reoperation, defined as repeated sterilization. The authors also note that the number of implant-based female sterilizations has increased by 27 times since 2005.

A 10-fold higher risk of repeated sterilization

The heightened risk of reoperation can be worrisome for some women, says Samantha Pfeifer, a gynecologist at Cornell University and a co-author of the study. But the proportion of women who undergo reoperation remains fairly low. "There is a 2.4 percent chance of needing a reoperation," she says. "So if you look at it from that perspective, there is a relatively small risk of needing one."

The researchers don't know why the Essure device causes problems for some women. The device could be flawed in some fundamental way. It's also possible that some doctors aren't placing it correctly, leading to migrations or perforations. Finally, some patients have it removed because of a nickel allergy, Pfeifer says. But it's unclear how many women experience this problem.

"This is a timely and important topic," says Aileen Gariepy, obstetrician-gynecologist at Yale University who didn't work on this study, and "this study is an important step." Zain Al-Safi, obstetrician-gynecologist at UCLA, agrees. Doctors will be able to use this information "when counseling women on the appropriate procedure for them and mention these possible risks," he says.

The study has some limitations. Women who get the Essure implant, for instance, have to get a checkup three months after the procedure. But this checkup isn't required for women who undergo laparoscopic sterilization, which means that complications from that procedure might not always get picked up by doctors, Pfeifer says. Still, "that doesn't detract from issues of pain and other complications that occur with the Essure," she says. The study also didn't determine which reoperations took place following the implantation of the Essure device or the briefly-sold Adiana system.

"This observational study has a number of limitations and makes several assumptions that require clarification to prevent misunderstanding among patients and healthcare professionals," Rosemarie Yancosek, a spokesperson for Bayer, told The Verge in an email. For example, the study is based on a single database of one US state, and it's unclear if the data includes patients who underwent Essure in office settings, she said. "Bayer is fully committed to helping provide physicians the tools they need to appropriately counsel women when they are considering Essure."

The researchers don’t think the device needs to be removed from the market

Pfeifer and her team don’t think the device needs to be removed from the market. Rather, they want a large, multi-center study to follow women’s outcomes after these procedures.

Overall, the study is concerning, but it's not the final word on the issue. Pregnancy can also be risky, so problems related to this implant will have to be weighed against the potential benefits of avoiding a birth. The FDA has yet to make a decision regarding the Essure device, so it's possible that they will rule against it. But in the meantime, the information from this study might help women make a better decision for their health.

Update 8:39PM ET: This story has been updated with a response from Bayer.