A federal appeals court has upheld a decision permanently blocking a 2013 Arkansas law that sought to ban abortions after 12 weeks gestation.

Reproductive rights groups had denounced the measure as one of the most extreme abortion bans in the country.

The three-judge panel of the Eighth US Circuit Court of Appeals ruled on Wednesday that the state regulation imposed an undue burden on a woman’s ability to terminate her pregnancy before fetal viability.

Medical experts say that generally a fetus may not survive outside the womb until 24 weeks gestation, and that a fetus is never viable at 12 weeks.

The Arkansas law sought to bar abortions after 12 weeks whenever an examination revealed a detectable heartbeat.

The law also required the physician to make an informed disclosure to the woman about the existence of the heartbeat and the probability of eventually giving birth.

The federal judge struck down the 12-week abortion ban last year, but upheld the testing and informed disclosure parts of the law.

The Arkansas law is among a barrage of new restrictions on abortions passed by conservative lawmakers at the state and federal level in recent years. A North Dakota law barred abortions after six weeks. That provision was struck down by a federal judge in a case now pending on appeal.

Twelve states – including Arkansas – have enacted 20-week abortion restrictions. And two weeks ago, Congress passed a bill that would ban all abortions nationwide after 20 weeks. The vote was 242 to 184. That bill is based on the assertion that an unborn child can feel pain starting at about 20 weeks of gestation.

It is unclear when, or if, the Senate will take up the measure. In the Arkansas case, the 12-week ban was passed after lawmakers overrode the veto of Gov. Mike Beebe.

Three groups, the Center for Reproductive Rights, the American Civil Liberties Union, and ACLU of Arkansas, filed suit on behalf of two Little Rock physicians and their patients.

US District Judge Susan Webber Wright ruled that the 12-week requirement amounted to an unconstitutional ban on abortion.

In affirming that decision on Wednesday, the appeals court said the law blocked a woman’s right to terminate her pregnancy before viability. But the court also signaled the potential for increased litigation in this area.

In their nine-page per curium ruling, the judges noted that in the four decades since the Supreme Court’s decision in Roe v. Wade, scientific advancements have moved the point of viability earlier in a pregnancy.

The judges complained that lawyers for the state had failed to offer any medical evidence challenging an assertion by the plaintiffs’ expert that a “fetus at 12 weeks is not and cannot be viable.”

“This case underscores the importance of the parties, particularly the state, developing the record in a meaningful way so as to present a real opportunity for the court to examine viability, case by case, as viability steadily moves back towards conception,” the court said.

The appeals court noted that in October 2006, a girl was born in Miami after 21 weeks and six days gestation. She was considered the youngest fetus to ever survive delivery. The court said she weighed less than 10 ounces and was nine inches long.

Reproductive rights groups praised the appeals court decision to block the 12-week ban.

“Today’s ruling affirms that safely and legally ending a pregnancy remains a protected constitutional right in this country,” Nancy Northup, president of the Center for Reproductive Rights, said in a statement.

“Women should not have to run to court in state after state, year after year to protect their constitutional rights from these politically-motivated attacks,” she said.

“The Constitution and the courts are clear: A woman’s right to decide for herself whether to continue or safely and legally end a pregnancy does not change depending on what state she happens to live in,” Ms. Northup said.

Officials with the ACLU’s Reproductive Freedom Project called the Arkansas 12-week ban “flatly unconstitutional.”

“This law was about banning abortion, plain and simple,” the ACLU’s Talcott Camp said in a statement. “Other states looking to pass similar laws should pay close attention.

Again and again, the courts have struck down these types of laws,” she said.

“It’s long past time legislators stopped trying to push their own politics on a woman who has decided to have an abortion,” Ms. Camp said.

The case was Edwards v. Beck (14-1891).