Women implanted with Bayer AG's Essure permanent contraception device were more than 10 times more likely to require post-procedure surgery than those who underwent laparoscopic sterilization, a study published on Tuesday found.

The findings could cast additional doubt on the safety of the Bayer device, which was approved in 2002 as an alternative to surgical sterilization and acquired by Bayer in 2013. It has faced recent scrutiny from U.S. health regulators following numerous patient complaints and calls for its withdrawal from the market.

By one year after the initial procedure, 2.4 percent of Essure patients had required follow-up surgery compared with 0.2 percent of those who underwent the minimally-invasive tube tying procedure, laparoscopic sterilization, researchers found. That translates to about 21 additional surgeries per 1,000 patients receiving Essure, they said.

"Small risk in large numbers of patients translates into large numbers," said study leader Dr. Art Sedrakyan, professor of healthcare policy and research at Weill Cornell Medicine in New York.

"In some instances, these re-operations are quite major surgeries" including hysterectomies, he added.

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The study, which analyzed coding data on medical records of some 52,000 women from outpatient ambulatory surgical centers in New York state between 2005 and 2013, was published in the British Medical Journal.

If the New York data were to be extrapolated to Essure use throughout the United States, you come up with about 150,000 patients getting this type of additional surgery, Sedrakyan said.

Both methods of contraception were equally effective, with about a 1 percent risk of unintended pregnancies.

Bayer, in a statement, defended the safety and efficacy of its device and cited limitations of the study, including that it was "based on a single database of one U.S. state" and unclear if it included patients who had Essure implantation in doctors' offices.

Bayer estimates there are about 750,000 women using Essure worldwide, about 70 percent of them in the United States.

Essure consists of two small nickel-titanium coils inserted into the fallopian tubes. Scar tissue forming around the device prevents pregnancy.

Personal injury lawsuits filed against Bayer have claimed the implant led to allergic reactions to nickel, severe pelvic pain, and surgeries to stabilize or remove the device after it shifted. More than 5,000 adverse events have been reported to the U.S. Food and Drug Administration, though it is not always clear what role Essure played in any event.

The FDA last month convened an advisory panel to mull the benefits and risks of Essure, and discuss whether it should face restrictions or label changes. The agency, calling it a high priority issue, said it will review the study findings, its panel's recommendations and public comments "to determine what future actions may be appropriate" regarding Essure.