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Why science can't settle the emergency contraceptive debate

Mark Wilson / Getty Images News

At the heart of the Hobby Lobby lawsuit was a very basic belief, held by the craft chain store's Pentecostal owners: that four types of FDA-approved birth control can cause abortions.

"If the owners comply with the HHS mandate [to provide birth control coverage for its employees]," the craft-store chain's lawyers argued in the lawsuit, "they believe they will be facilitating abortions."

The Supreme Court largely left this issue aside, dealing instead with the legal questions of whether Hobby Lobby, as a corporation, could exercise religious freedom. But the issue  Hobby Lobby raised—that certain contraceptives are abortifacients, or "abortive pills" as Mitt Romney once called them—is one scientists have grappled with in the course of years of research.

Based on the most recent evidence, their general conclusion is this: while one of the four forms of birth control at issue—the copper IUD—may disrupt the implantation of a fertilized egg when it's used as an emergency contraceptive, the others can't.

In the view of some religious groups, which see life as beginning at conception, disrupting implantation—when a fertilized egg embeds itself in the uterine wall—could be considered abortion. But that's not how the international medical establishment sees things. Here's why.

How emergency contraceptives work

The groups that brought the case against the birth control mandate opposed the mandatory coverage of two "morning after pills" Plan B and Ella, as well as the intrauterine devices ParaGard and Mirena.

There's a definitive body of research showing that the morning-after pill doesn't stop fertilized eggs from implanting on the uterine wall, despite what their labels say. That's because they work pre-fertilization, which is why they need to be taken soon after unprotected sex. Plan B and Ella act hormonally, by preventing or slowing down ovulation or by changing the amount and consistency of cervical mucus to create an environment where sperm will not survive. When taken too late, after ovulation or fertilization, these medicines don't work. (It's important to note that Mirena also acts hormonally, but unlike the other two "morning-after pills," it's an IUD used for regular and not emergency contraception.)

That leaves the ParaGard, a copper device and the only IUD approved by the FDA for emergency contraception as well as regular birth control. It works differently than the latter three contraceptives. And that's why researchers haven't been able to rule out the possibility that it prevents a fertilized egg from implanting on the uterine wall.

Unlike the morning-after pill, ParaGard is hormone-free: it works locally and can have an effect after fertilization has occurred. When it's used for regular birth control, it mainly prevents sperm from fertilizing an egg by creating a toxic environment in the uterus where these gametes can't survive. But when the T-shaped, copper device is inserted into a woman's uterus in emergencies, fertilization may have already occurred. Dr. Mario Ascoli, a professor of pharmacology at the University of Iowa, explained that since copper is toxic to sperm and eggs, it could be toxic to a fertilized egg already present when the IUD was inserted. "In some people, it may actually have an effect on implantation—but only when it's used for emergency contraception."

This is why it's considered the most effective form of emergency contraception, and why groups like Hobby Lobby don't want to cover it. Still, according to recent studies on the copper IUD, stopping pregnancy by preventing implantation is a very uncommon method of action.

Scientists and religious groups have different definitions of pregnancy

This science didn't stop the folks behind Hobby Lobby from making their case. But that's because the debate is not really about science; it's about the fundamental question of when pregnancy begins and when society should intervene to protect human life.

According to federal regulations, pregnancy starts later, after implantation when the embryo has already found a home in the lining of a woman's uterus. This view is supported by the American Medical Association, the American Congress of Obstetricians and the National Institutes of Health, among other science-based groups. Based on this definition, medicines like ParaGard, Ella, and Plan B were approved as contraceptives and not abortifacients. (The only drug approved to induce abortion is RU-486.)

For others, including some religious conservatives, pregnancy starts early on with conception: when the sperm fertilizes an egg. So that pre-implantation ball of cells, which has about a 20 percent chance of survival, is a nascent life. Anything that curbs its potential for growth, under this view, is considered the termination of a pregnancy.

So if you believe that pregnancy begins when egg and sperm swap genetic material—which, again, is not how the scientific establishment views this—an emergency contraceptive that possibly prevents implantation could be considered a pregnancy ended. It also means that research hasn't completely ruled out the possibility that ParaGard, the copper IUD, could cause that ending.

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