A US appeals court has struck down Idaho's ban on abortion after 20 weeks of pregnancy.

In a ruling issued on Friday, the 9th Circuit Court of Appeals in San Francisco, California, affirmed a lower court's decision and declared that Idaho's Pain-Capable Unborn Child Protection Act or Section 18-505 as "facially unconstitutional because it categorically bans some abortions before viability."

The decision stemmed from the case of plaintiff Jennie Linn McCormack, who self-aborted in 2010 using abortion pills bought online for $300 by her sister and shipped to her in Idaho.

McCormack was criminally charged in May 2011 by the prosecuting attorney in Bannock County, Idaho, for violating Idaho Code 18-606 for purposely terminating her own pregnancy.

McCormack told the police that she self-induced an abortion by ingesting a pack of five pills. A physician who examined her foetus estimated the gestational age to be between 19 and 23 weeks "but with difficult certainty."

An Idaho judge dismissed the criminal complaint in September 2011.

Despite her victory, McCormack filed a class action suit challenging Idaho's abortion statutes.

US District Judge Lynn Winwill ruled in 2013 against Idaho's ban on abortion.

"The state's clear disregard of this controlling Supreme Court precedent and its apparent determination to define viability in a manner specifically and repeatedly condemned by the Supreme Court evinces an intent to place an insurmountable obstacle in the path of women seeking non-therapeutic abortions of a non-viable fetus at and after 20 weeks gestation," the ruling said.

The appeals court said McCormack's challenge to the 18-606 law "is not moot because her claims fall under three exceptions to the mootness doctrine," which are voluntary cessation, collateral legal consequences and capable of repetition yet evading review.

"McCormack has standing based on the lingering risk of prosecution under 18-606," the court said.

It declared that Idaho's Section 18-505, which prohibits abortion on unborn child that is 20 or more weeks, "is facially unconstitutional because it categorically bans some abortions before viability."

The appeals court also declared Section 18-608 (2) as "facially unconstitutional because it places an undue burden on a woman's ability to obtain an abortion by requiring hospitalizations for all second-trimester abortions."

It also said the Section 18-608 (1) in conjunction with 18-605 is "unconstitutionally vague."

Meanwhile, the 8th Circuit Court of Appeals has upheld a lower court's decision and struck down an Arkansas law that prohibited abortion at 12 weeks of pregnancy.

"By banning abortions after 12 weeks' gestation, the act prohibits women from making the ultimate decision to terminate a pregnancy at a point before viability," the appeals court said, according to Reuters.

Arkansas' Act 301 banned abortion when a heartbeat is detected at 12 weeks or more of pregnancy.

The court said it violated a woman's right to terminate a pregnancy at a point before the viability of the foetus.

According to the appeals court, it is bound by the 1992 US Supreme Court ruling upholding the right to have an abortion before viability and Arkansas did not refute the assertions of the doctors' lawyers.