Supporters of abortion rights voiced trepidation outside the United States Supreme Court on Wednesday as justices weighed the fate of one of the numerous restrictive laws passed by conservative states which make access to the procedure more difficult.

Hundreds of demonstrators rallied on a cool and sunny day in the US capital as the nine justices heard arguments in Shreveport abortion clinic's appeal of a lower court ruling that upheld a restrictive Louisiana abortion law. Abortion rights supporters outnumbered opponents. Some carried signs saying "Protect Safe, Legal Abortion" and "My Right, My Decision".

"I remember a time when abortion wasn't legal. It was illegal when I was a teenager. And we aren't going back. We're just not going back," said demonstrator Bambi Nelms, 62, of Maryland. "My mother had an illegal abortion before I was born - coat hanger variety - and it darned near killed her. She had me after that."

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Louisiana's law, put on hold during the legal challenge, requires doctors who perform abortions to have a sometimes difficult-to-obtain arrangement called "admitting privileges" at a hospital within 30 miles (48km) of the abortion clinic.

Abortion rights advocates have argued that restrictions such as admitting privileges are meant to limit access to abortion, not protect women's health as proponents say.

Steffani Bangel, 30, who works at a Louisiana organisation that supports access to abortion clinics, noted that the Supreme Court in 2016 struck down a Texas abortion law that contained an admitting privileges mandate.

"It's frustrating to be back here after four years. We were just here four years ago," Bangel said.

"We believe the law is on our side," Bangel added.

Today, SCOTUS is hearing a case on Louisiana’s clinic shutdown law. Today, we are reaffirming that abortion care IS healthcare. Every person, regardless of income, sexual orientation or gender, deserves equitable access to comprehensive reproductive healthcare #MyRightMyDecision pic.twitter.com/360k78yJgz — Congresswoman Ayanna Pressley (@RepPressley) March 4, 2020

Activists who oppose abortion are hoping the Supreme Court, with a 5-4 conservative majority, will scale back or even overturn the landmark 1973 Roe vs Wade ruling that legalised abortion nationwide.

Some anti-abortion demonstrators held flags emblazoned with Bible quotes and the image of a bald eagle - a symbol of the US - carrying a Christian cross. Others stood silently with red tape over their mouths with the word "LIFE" in black letters.

Demonstrator Dennis McKirahan, 75, of Ohio said supporters of abortion rights were "distorting what God intended".

"When that baby is a seed in the womb, scientifically, it's going to be a baby. And you can't stop that or you're killing that baby," McKirahan said. "God didn't intend us to stop our creation."

Louisiana's law is one of many passed in conservative states to restrict abortions. Others enacted in recent years bar abortions after a certain number of weeks of pregnancy, require ultrasound exams and state-mandated counselling for women, and impose waiting periods and compel parental consent for minors seeking the procedure.

Lillian Kaminer, 69, of Virginia said she attended the rally because preserving access to abortion is her "number one political cause".

"Women should have a choice about their health, their healthcare and their families," Kaminer said.

The court on Wednesday heard about an hour of arguments in an appeal by Shreveport-based abortion provider Hope Medical Group for Women seeking to invalidate the 2014 law. Two of Louisiana's three clinics that perform abortions would be forced to close if the law is allowed to take effect, according to lawyers for the clinic.

Some conservative judges signalled sympathy towards Louisiana's law. Chief Justice John Roberts, a conservative considered the court's ideological centre and a potentially decisive vote, asked questions that seemed to focus on whether he felt bound by the court's 2016 ruling when it struck down similar restrictions in Texas.

Roberts cast the deciding vote when the justices last year on a 5-4 vote blocked Louisiana's law from taking effect while the litigation over its legality continued.

That vote brings him into conflict with his position in the Texas case, when Roberts was among the three dissenting judges who concluded that an admitting privileges requirement did not represent an undue burden.

Divisive social issue

During Wednesday's arguments, his questions indicated that the chief justice may feel that he is bound by the 2016 court's finding that admitting privileges laws provide no health benefit.

Two of the court's conservatives, Justice Neil Gorsuch and Justice Clarence Thomas, said nothing during the arguments.

The liberal justices, including the three women on the court, appeared sceptical towards the admitting privileges provision.

Justice Sonia Sotomayor said it was a "mystery to me" why a 30-mile limit was imposed if the intent of the law was to show that doctors were properly credentialled.

Justice Ruth Bader Ginsburg made a similar point, noting that medical complications for women who undergo abortions generally occur at home, meaning that the fact the doctor has a relationship with a nearby hospital is irrelevant.

"That's what I don't understand," Ginsburg said.

A federal appeals court upheld the law. President Donald Trump's administration supports Louisiana in the case.

The Supreme Court struck down a similar Texas admitting privileges requirement in 2016 when conservative Justice Anthony Kennedy, who retired in 2018, joined the four liberal judges to defend abortion rights. Trump has tightened the conservative grip on the court with his 2018 appointment of Justice Brett Kavanaugh, who replaced Kennedy, and his 2017 appointment of Justice Neil Gorsuch.

An anti-abortion demonstrator holding a mock human foetus outside the US Supreme Court during a protest on Capitol Hill in Washington, DC [Tom Brenner/Reuters]

Neither Kavanaugh nor Kennedy ruled directly on abortion rights during their prior service as federal appellate judges. Trump promised during the 2016 presidential race to appoint justices who would overturn the Roe vs Wade ruling. The Supreme Court in 1992 reaffirmed Roe vs Wade in a ruling that prohibited laws that placed an "undue burden" on a woman's ability to obtain an abortion.

The Louisiana case will test the willingness of the court to uphold Republican-backed abortion restrictions being pursued in numerous conservative states.

Baton Rouge-based US District Judge John deGravelles cited the undue burden precedent when he struck down Louisiana's law in 2016, prompting the state to appeal to the New Orleans-based 5th US Circuit Court of Appeals. The 5th Circuit upheld the law despite the 2016 precedent, concluding there was no evidence any Louisiana clinic would close due to the admitting privileges requirement.

Abortion remains one of the most divisive social issues in the US, with Christian conservatives - an important constituency for Trump - among those most opposed to it. A Supreme Court ruling in favour of Louisiana's law could prompt other states to pass similar statutes.