A Supreme Court ruling in favor of allowing companies to opt out of providing female employees some forms of birth control — such as the morning-after pill and certain IUDs — has allowed religious employers to “redefine” pregnancy in a way that flies in the face of the established science of conception, reproductive health experts say.

The company that brought the suit, Hobby Lobby, argued that using these types of contraceptives is tantamount to having an abortion, and, citing religious beliefs against terminations, wanted to opt out of the provision of the Affordable Care Act that requires companies to cover preventive services like contraceptives.

But reproductive health experts and the principal dissenting Supreme Court justice say a belief that emergency contraceptives and intrauterine devices, or IUDs, are so-called abortifacients is in direct opposition to widely established scientific definitions of pregnancy. They also say that the company’s interpretation of how the contraceptives terminate pregnancies is contrary to how they actually work.

National medical associations as well as the federal government define pregnancy as the implantation of the fertilized egg into the uterine wall.

Part of the controversy surrounding the Hobby Lobby case, however, lies in an apparent misconception over whether morning-after pills work to prevent a fertilized egg from implanting in the uterine wall, which is what the company has said it opposes on religious grounds.

“They believe that life begins with the gleam in the eye, or when the sperm meets the egg,” said James Trussell, a professor and emergency contraception expert at Princeton University’s Office of Population Research.

While Hobby Lobby’s consideration of pregnancy differs from the scientific definition, experts say all evidence has shown that the morning-after pill doesn’t prevent pregnancy after an egg has been fertilized anyway.

Trussell said that scientific studies of how morning-after pills such as Plan B and ella work show (PDF) that they prevent pregnancy either by inhibiting or preventing ovulation — when the ovary releases an egg and it travels down the fallopian tube.

Without ovulation having taken place, sperm cannot fertilize an egg, much less implant into the uterine wall.

“It’s very clear that none of [emergency contraception options] will work once pregnancy has started, and the legal definition of pregnancy is implantation,” Trussell said.

Morning-after pills are essentially stronger doses of hormones than those already found in regular hormonal birth-control pills — which Hobby Lobby did not object to in its legal challenge. But because emergency contraceptives have faced so much scrutiny from opponents who believe they abort pregnancies, scientists have done the research and found that the pills are not effective in preventing pregnancy if taken after ovulation has already happened, said Kelly Cleland, a researcher from Princeton’s OPR.

“The evidence is very, very clear that Plan B only works before ovulation,” she said. Once a woman ovulates, “you see that reflected in the failure rates” of Plan B. If the pill prevented implantation of a fertilized egg into the uterine wall, the process that scientists consider to be pregnancy, the failure rates would be lower than they are.

But complicating the picture, and lending credence to Hobby Lobby’s suit, is that Plan B has said on its website that the emergency contraceptive may also work by preventing the egg from being fertilized, or keeping the fertilized egg from implanting, rather than just in preventing ovulation.

Even if that were the case, however, the pill still does not claim to terminate an egg that has been implanted — the scientific definition of pregnancy.

Meanwhile, the copper-T IUD, a T-shaped device inserted into the uterus, is typically used to prevent sperm from reaching the egg. It can also be inserted into the uterus after intercourse as a method of emergency contraception.

While the IUD hasn’t had the same level of scrutiny as emergency contraceptives, Cleland said copper ions in the copper-T are toxic to sperm and prevent fertilization of the egg, and that “there is certainly no evidence that it would interrupt an established pregnancy.” Hormonal IUDs release hormones that are the same as those used in hormonal birth-control pills to prevent pregnancy.

However, IUDs’ extremely low failure rate — about one pregnancy in every 1,000 uses, compared with Plan B or ella, which do not work about 2.2 percent and 1.4 percent of the time, respectively — indicates they may prevent implantation. Some studies have also supported that theory, which is why some companies oppose them on religious grounds.

Ella is a newer pill that uses a different hormone and can prevent ovulation slightly later in a woman's cycle, making it more effective at preventing pregnancy.

Trussell and Cleland, along with a coalition of several national reproductive and women’s health groups including the American College of Obstetrics and Gynecology (ACOG), the American Society for Reproductive Medicine (ASRM) and the American Medical Women’s Association, submitted a friend-of-the-court brief to the Supreme Court in support of the government’s position on the case, asserting that the contraceptives in question do not work by preventing implantation.

The brief argued that the “claim that Plan B and ella prevent implantation is not supported by current scientific data or by evidence … to the contrary, scientific research shows that Plan B and ella both function by inhibiting or postponing ovulation; they do not prevent fertilization or implantation.”

They also cited research suggesting that “even under optimal conditions and timing,” only 40 percent of fertilized eggs successfully implant (PDF) in the uterine wall, meaning that a lack of implantation is common with or without the use of contraception.

The Department of Health and Human Services defines pregnancy as “the period of time from implantation until delivery,” as outlined in its regulations governing the use of human subjects for research.

And the FDA in 1997 released a notice about emergency contraception (PDF), saying that these options “are not effective if the woman is pregnant; they act by delaying or inhibiting ovulation, and/or altering tubal transport of sperm and/or ova (thereby inhibiting fertilization), and/or altering the endometrium (thereby inhibiting implantation).”

The friend-of-the-court brief submitted by ACOG, ASRM and other groups goes on to say that while Hobby Lobby and other companies “may have differing personal views as to when life begins, the medical and scientific communities define pregnancy as beginning upon implantation. While personal beliefs may dictate individual choices and values, they cannot alter established scientific standards and terminology: abortion refers to the termination of a pregnancy. Thus, the term 'abortifacient' refers to — and should only be used in connection with — drugs or devices that end a pregnancy, not those that prevent it.”

Indeed, in Supreme Court Justice Ruth Bader Ginsburg’s dissenting opinion on the Hobby Lobby case, she referenced both government-issued definitions of pregnancy.

She wrote, “The owners of the companies involved in these cases and others who believe that life begins at conception regard these four methods as causing abortions, but federal regulations, which define pregnancy as beginning at implantation, do not so classify them.”

As a result, Cleland, said Hobby Lobby and other companies “are really redefining what pregnancy is, and therefore what abortion is.”

She added, “I’m really shocked that it’s gone on unchecked.”

“You can believe one of two things,” said Trussell about the case. “Either they [the companies opposing use of emergency contraception] are very stupid, or they don’t believe in science. But there is no other explanation.”