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How do contraceptives work, and why are antiabortion advocates targeting them?

Some conservative politicians are taking aim at IUDs and the morning-after pill, saying life begins at conception.

An intrauterine device, known as an IUD.Adek Berry/Photographer: Adek Berry/AFP/Get

Medical experts are concerned that the fall of Roe v. Wade could threaten contraception access in several states, given the wording of a draft opinion leaked last week and the actions of conservative politicians in several states.

At the heart of the issue is the question of when pregnancy begins. Several conservative politicians and antiabortion groups have defined life as beginning at fertilization — instead of at implantation, a process that is not a given and can occur approximately a week later. Under that theory, which many doctors reject, a ban on abortion could threaten some methods of contraception, such as IUDs and morning-after pills, that can inhibit a fertilized egg from being implanted in the uterus. Some experts fear other contraceptive measures could also be at risk.

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Worries about birth control access started to swirl soon after Politico reported last week that the Supreme Court was preparing to strike down Roe, the landmark abortion decision, according to a leaked draft majority opinion. The court hasn’t issued a final decision.

But lawmakers have already begun to take action. In Louisiana, a proposal advancing in the state Legislature defines personhood as beginning “from the moment of fertilization” and seeks to treat abortion as homicide.

In Idaho, a leading Republican said he supported state hearings on legislation that would ban emergency contraception — or measures to prevent pregnancy after unprotected sex — in addition to abortion pills. He later clarified that the hearings would be to discuss alleged safety concerns with emergency contraceptives.

The tactic aligns with that of several antiabortion groups, which consider birth control pills and IUDs as “abortifacients,” or substances that can induce abortions, because they can inhibit the implantation of a fertilized egg. On its website, Students for Life of America lists birth control pills and IUDs as being “capable of unnaturally ending the life of a preborn child,” though the group is not formally opposed to condoms, diaphragms, or spermicide. Mother Jones reported last week that members of antiabortion group Heartbeat International had already begun discussions of how to expand the definition of abortion to include a wide range of contraception at their annual meeting.

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Fertilization does not mean pregnancy, some experts say

There is little debate about the mechanics of pregnancy: After intercourse, sperm travels through the uterus and into the fallopian tubes to fertilize an egg during ovulation. This process can take up to five or six days, depending on the timing of an individual’s cycle. Fertilization takes approximately 24 hours, and then it can take three to four days for a fertilized egg to reach the uterus and another two to six days for it to implant itself into the lining of the uterus.

Between a third and half of all fertilized eggs will never implant, studies estimate. A pregnancy test only reads positive about a week after implantation is complete.

Many medical experts, including the American College of Obstetricians and Gynecologists, agree that pregnancy begins when a fertilized egg implants in the uterus, and not before.

“The Republicans are trying to say that fertilization is when they should worry and be involved,” said Dr. Kellie Lease Stecher, cofounder of Patient Care Heroes, which helps health care workers with mental health needs, and a practicing OGYN in Minnesota. “Medically, if you don’t have an implanted embryo or fetus, you aren’t having a positive pregnancy test. It’s floating around, no one should care. This shouldn’t be a thing.”

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How different forms of birth control work

Contraception inhibits pregnancy in several ways. Birth control pills can prevent a person from ovulating, so there is no egg to fertilize. They also thin the lining of the uterus, which helps prevent implantation in the event an egg is released and is fertilized.

Intrauterine devices, known as IUDs, that contain hormones also partially suppress ovulation. They also work to thicken the mucus in the cervix — stopping sperm from getting into the uterus — and thin the lining of the uterus.

Copper IUDs release copper ions into the uterine cavity, which are toxic to sperm. The ions also can prompt an inflammatory response, disturbing the functioning of the uterine lining. While Lease Stecher said it can be difficult to get an appointment for an IUD within the necessary window after unprotected sex, copper IUDs can be used up to five days after unprotected sex to reduce the risk of pregnancy by 99 percent.

The morning-after pill delivers a dose of progesterone, which changes the lining of the fallopian tubes — which eggs pass through on their way to the uterus — making it more difficult for sperm to reach the egg. Progesterone also thins the lining of the uterus. Notably, the morning-after pill has no effect on an embryo that has already implanted in the uterus, nor does it harm a fetus, as progesterone is also present during pregnancy.

Nexplanon, a contraceptive implant, also works by delivering a dose of progesterone, inhibiting ovulation, thickening cervical mucus, and thinning the lining of the uterus.

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Preventing implantation is not abortion, many doctors say

Lease Stecher is concerned that antiabortion lawmakers could target most forms of contraception, because so many help prevent implantation — even if some of the ones that help prevent implantation also don’t allow an egg to be fertilized.

“Anything with progesterone will thin the uterine lining,” she said. “Where does the argument stop?”

Dr. Katherine Pocius, medical director of family planning at Massachusetts General Hospital, added that prevention of implantation is not the same as an abortion.

“Clinically, no methods of birth control are abortifacients, but lack of science hasn’t stopped Republican lawmakers from making claims in the past,” she said.

A chilling effect

Experts continue to debate how imperiled contraception will be should Roe v. Wade be overturned. But no matter the outcome of legislation that threatens access to contraception, advocates still worry that the language will have a chilling effect on the willingness of doctors to prescribe certain types of birth control.

“It is very extreme, and I think there is a lot of uncertainty,” said Michelle Erenberg, cofounder and executive director of Lift Louisiana, a nonprofit focused on women’s health.


Jessica Bartlett can be reached at jessica.bartlett@globe.com. Follow her on Twitter @ByJessBartlett.