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Healthy Living

How IUDs Really Work (No, They Don't Terminate Pregnancies)

Some people clearly need a reminder.

As more women turn to long-lasting and highly effective IUDs for birth control, some anti-abortion groups are hitting back with a bogus health claim that IUDs are "life-ending" abortion devices.

The groups are ramping up the attack on IUDs in advance of the U.S. Supreme Court's decision to take on the "contraceptive mandate," a case that that pits the Affordable Care Act against a collection of religiously affiliated colleges and nonprofits that are opposed on religious grounds to including employees' birth control in their health insurance policies.

Anti-abortion groups opposed to IUDs hold that conception occurs -- and therefore life begins -- when an egg is fertilized by sperm. Any birth control method that prevents a fertilized egg from implanting in the uterus, therefore, is abortion. (The most extreme arguments take this so far as to claim that any artificial birth control method that prevents pregnancy, including condoms and birth control pills, is essentially an abortion.)

On the other side are the majority of doctors and the U.S. Department of Health and Human Services, which defines pregnancy as "the period of time from implantation until delivery."

We'll leave the philosophical debate about what constitutes life for another day, but even by the non-medical, fertilized egg definition, IUDs still aren't abortion devices.

"It's completely misleading," Amy Bryant, an assistant professor of obstetrics and gynecology at the University of North Carolina, said of the term "life-ending device."

"It makes it seem like having an IUD in place is the same as having an abortion on a regular basis, which doesn't really make any sense," she said. "That's not their mechanism of action."

How the hormonal IUD works

There are two types of IUDs. The hormonal IUD prevents pregnancy when implanted in the uterus by releasing low levels of progestin, a synthetic version of the naturally occurring hormone progesterone. The progestin thickens the cervical mucus and thins out the uterine lining, creating a hostile environment where the sperm can't reach the egg. While experts can't say with 100 percent certainty exactly which of these actions is responsible for pregnancy prevention at any given time, none of them stops a fertilized egg from implanting in the uterus. Instead, the mechanisms stop an egg from being fertilized in the first place.

And even if a woman were to get pregnant while using the hormonal IUD (chances of which are very close to zero), the hormonal IUD wouldn't hurt her pregnancy, which is why hormonal IUDs aren't used as emergency contraception, according to Bryant. In fact, in this unlikely situation, the progestin in the IUD might actually help the pregnancy, since the body naturally releases the hormone after fertilization.

How the hormone-free copper IUD works

The copper IUD works a little bit differently. It's hormone-free and works by releasing copper ions that trigger a sterile inflammatory response, disabling sperm and thereby making it difficult for sperm to meet and fertilize the egg.

As for the argument that a fertilized egg could be implanted in the uterus and subsequently dispelled by an IUD, Dr. Carolyn Alexander of the Southern California Reproductive Center called the situation "theoretically possible," but extremely rare.

Bryant framed it a different way. "There are plenty of times in a natural cycle where an egg is fertilized but it doesn't implant. Does that mean there was a miscarriage?" she asked.

Unlike the hormonal IUD, the copper IUD can be used as an emergency contraceptive method up to five days after unprotected sex or birth control failure. In that case, the device may disrupt a fertilized egg, again, in a small number of cases. Of course, that's assuming the woman is pregnant in the first place. "When people are not using any sort of contraception, they don't get pregnant every single time that they have sex," Bryant said. "There's a lot of different factors that go into whether a fertilized egg become a pregnancy or not."

The bottom line is that the mechanism of action for hormonal and non-hormonal IUDs isn't to prevent implantation of a fertilized egg at all. It's to prevent the egg from being fertilized in the first place. Could a series of low-probability events disrupt a fertilized egg? It's possible, but highly unlikely.

A win for anti-abortion groups is a loss for public health

It's a shame that the issue is so contentious, because from a public health standpoint, IUDs are a superb birth control method. In addition to being 45 times more effective than typical birth control pill use and 90 times more effective than typical male condom use, IUDs are also the most commonly used reversible contraceptive in the world, according to Columbia University's Mailman School of Public Health.

The United States has seen a spike in IUD use over the past decade, with one in 10 women who use contraception relying on the IUD -- up from only 2 percent of contraceptive users in 2002.

IUDs are also notably the most popular personal birth control method among female women's health providers, a full 40 percent of whom have an IUD. Know what else these women have? A sound understanding of what constitutes abortion.

Also on HuffPost:

10 Must-Know Birth Control Facts