Implanon: The birth control that's getting lost in women's bodies

The beauty of contraceptive implants is that, once a doctor has tucked one under a woman's skin, she shouldn't have to worry about birth control for several years. At least, that's the theory. But hundreds of British women who were using an implant called Implanon nevertheless wound up pregnant last year and — after visiting doctors to have the implants removed — discovered that the implants were nowhere to be found. What's behind this deeply troubling mystery, and what are the consequences? Here, a brief guide:

What is Implanon?

It's a match stick-sized device that is placed under the skin in a fat layer of the upper arm. It's designed to release hormones that stop ovulation, preventing conception for up to five years. It's a fairly simple procedure, and the implant can be taken out at any time. But it must be put in, and taken out, by a doctor.

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How popular is Implanon?

Considerably. Implanon was licensed in 1999, and the British Department of Health says 800,000 women in the country use it. A quarter of women who go to U.K. family planning clinics get Implanon or a similar form of implantable birth control. Implanon is the top choice for women over 30 and under 20 at the country's National Health Service. It's especially popular with teenagers, 10 percent of whom say they prefer implants to the pill because they don't have to remember to take it. Used properly, it's 99.95 percent effective — a fraction of a percent better than the pill.

So what's the problem?

It's not always used properly. There have been some cases in which the implant never got released from the pre-loaded applicator, so the women thought they had birth-control protection, but didn't. In other cases, doctors have put implants in too deep in the patient's arm for it to do much good. There have also been cases in which Implanon implants have come loose from the fat that is meant to keep them in place, and migrated to other spots in the body.

Is that a problem?

Yes, especially for women near the end of their childbearing years, who want the implants removed so they can get pregnant before it's too late. One such patient, Nici Davies, 37, got an implant in 2010. The Londoner was told it would be no problem to remove it if she decided to have kids. Well, she did, and went in to have it removed in April, only to have three doctors fail to find it. Now Davies is afraid that by the time the device stops working she won't be able to get pregnant. "The implant can last five years, she tells Britain's The Sun. "I am left with no chance of having children."

Can the drug maker fix this?

Implanon's manufacturer MSD, a subsidiary of pharmaceutical giant Merck, replaced Implanon with an updated version called Nexplanon — available in the U.K. and U.S. — that has a new, improved applicator. It also contains barium, which makes it easier for doctors to track it down if it gets loose. But the company hasn't recalled Implanon that's already out there. A spokesperson for the company says the missing implants are usually just in too deep, and rarely actually move around, and that doctors have ways to find them. Still, says Lindsay Cross at Mommyish, knowing that there are any women out there who are stuck with a "missing matchstick floating around inside of them releasing hormones" is, or should be, a PR disaster.

Sources: Daily Mail, Mommyish, Sun