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The U.S. Supreme Court today rejected an appeal from North Dakota to revive its proposed restriction on abortions, which would be the strictest in the nation.

By declining to take up the case, the justices left lower court rulings standing that found the restriction unconstitutional and blocked the law's enforcement. Passed in 2013, it was intended to make abortions illegal after a fetal heartbeat could be detected — about six weeks into the pregnancy.

Meet the Press/American Communities Project

Earlier this month, the Supreme Court turned away an appeal from state officials in Arkansas who sought to revive a similar fetal heartbeat law. Also blocked by lower courts, it would have banned abortions after about 12 weeks of pregnancy.

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In both cases, the US Court of Appeals for the Eighth Circuit — responsible for federal cases Arkansas, North Dakota, and five other states — said it was bound by an earlier U.S. Supreme Court decisions on abortion. Those precedents say the states may not impose undue burdens on a woman's right to choose during the period of pregnancy before the fetus is viable.

Related: U.S. Supreme Court to Rule on Abortion Limits

Even so, the appeals court said, "good reasons exist" for the Supreme Court to revisit those cases. "The continued application of the Supreme Court's viability standard discounts the legislative branch's recognized interest in protecting unborn children," the Eighth Circuit said in the North Dakota case.

But the Center for Reproductive Rights, representing the only abortion clinic in North Dakota, urged the Supreme Court to leave the ban on the North Dakota law in place.

"Since this Court first recognized constitutional protection for pre-viability abortion, two generations of American women have come of age, depending on constitutional protection for their dignity in making reproductive decisions."

The Supreme Court will decide the fate of another abortion restriction during this current court term. It's a challenge to a Texas law requiring abortion clinics to conform to the same building standards as surgical centers. It also requires doctors performing abortions to have admitting privileges at nearby hospitals.

Since the law was passed, the number of abortion clinics in Texas has fallen from 42 to 19, and could drop to ten if the law is upheld.

The justices will hear the Texas case in March with a decision expected by late April.