WASHINGTON (Reuters) - The U.S. Supreme Court on Monday rejected North Dakota’s bid to revive a restrictive Republican-backed law struck down by a lower court that would ban most abortions once a fetal heartbeat can be detected, as early as six weeks after conception.

The court turned away the state’s appeal, leaving in place a July 2015 ruling by the 8th U.S. Circuit Court of Appeals that blocked the 2013 law. North Dakota’s law was among the strictest of a series of statutes passed at the state level imposing limits on abortion.

The law was challenged by North Dakota’s only abortion clinic, the Red River Women’s Clinic in Fargo.

In a separate case, the high court is due to hear arguments on March 2 in a challenge by abortion providers to parts of a restrictive, Republican-backed Texas law they contend are aimed at shutting clinics that perform the procedure. It will be the court’s first abortion case since 2007.

In the North Dakota case, the appeals court had said it was bound in its ruling by U.S. Supreme Court precedent on abortion, which holds that states may not prohibit abortions before a fetus reaches viability. But the appeals court said “good reasons exist” for the high court to re-evaluate its past abortion decisions in light of medical and scientific advances that show the concept of viability is subject to change.

Republican backers of the North Dakota law had said 40 years of medical advancements should not be ignored. Opponents said a ban at six weeks would mean abortion would be outlawed at a gestation time when many women do not yet even know they are pregnant.

On Jan. 19, the high court refused to hear a similar case in which Arkansas sought to revive a Republican-backed law also blocked by lower courts that would ban abortions after 12 weeks of pregnancy.

The high court legalized abortion in 1973, but abortion remains a contentious issue among Americans. Some states, particularly those governed by Republicans, have sought to chip away at a woman’s right to end a pregnancy by passing laws imposing a number of restrictions.

Viability, according to medical experts, occurs around 23 to 24 weeks into a pregnancy. Lawmakers in North Dakota, Arkansas and other conservative states have sought to ban abortions at an earlier stage, citing among other things hotly debated medical research suggesting a fetus feels pain starting at 20 weeks of gestation.

The North Dakota case was 15-627, Stenehjem v. MKB Management, U.S. Supreme Court, No. 15-627.