A federal judge in Mississippi on Friday blocked a state law that prohibited abortions after a fetal heartbeat is detected, around six weeks into pregnancy. U.S. District Judge Carlton Reeves said in the ruling that the law "prevents a woman's free choice, which is central to personal dignity and autonomy."

"S.B. 2116 threatens immediate harm to women's rights, especially considering most women do not seek abortion services until after 6 weeks. Allowing the law to take effect would force the clinic to stop providing most abortion care," Reeves wrote.

Reeves, an Obama-appointed judge, also struck down Mississippi's 15-week ban late last year. The so-called "fetal heartbeat" bills ban an abortion as soon as six weeks, which is before many women know they are pregnant.

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Mississippi is one of several states that have passed restrictive abortion laws as anti-abortion activists have become more emboldened by a wave of conservative judge appointments. Anti-abortion activists hope these laws will be challenged in the courts, eventually challenging the landmark 1973 Supreme Court decision Roe v. Wade.

Three other states — Georgia, Kentucky and Ohio — have passed their own "fetal heartbeat" bills. Last week, Alabama's Gov. Kay Ivey signed one of the most restrictive abortion laws in the country and Missouri Gov. Mike Parson on Friday signed a law banning abortions at eight weeks. Louisiana Gov. John Bel Edwards, a Democrat who ran on an anti-abortion rights platform, has said he will sign his state's fetal heartbeat bill.

None of those bills are currently in effect. The ACLU and Planned Parenthood on Friday filed a lawsuit challenging Alabama's near-total abortion ban, and the ACLU challenged Ohio's bill last week. Kentucky's fetal heartbeat bill has been blocked by a federal judge.

In February, the Supreme Court temporarily blocked a Louisiana law that regulated abortion clinics from going into effect. A similar law in Texas in 2016 was struck down.

Women's reproductive rights advocates, like the ACLU and Planned Parenthood, have vowed to challenge Georgia's "heartbeat" bill long before January 2020, when it's scheduled to go into effect.