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FRANKFORT, Ky.— Already mired in three lawsuits over abortion restrictions, Kentucky lawmakers are ratcheting up the stakes with a new bill to ban most abortions once a fetal heartbeat is detected.

As a new legislative session opens, the measure appeared to be on a fast track in the Republican-dominated state Senate. The American Civil Liberties Union, the state's adversary in the ongoing courthouse fights, warns the heartbeat bill would prohibit most abortions in Kentucky and would immediately trigger a legal challenge.

"It's blatantly unconstitutional," ACLU attorney Brigitte Amiri said Wednesday, a day after the measure was introduced by lawmakers. "This is certainly the most blatant attempt to take aim at Roe vs. Wade. It's extreme. It's yet again anti-abortion politicians trying to push abortion out of reach for women in this state."

Kentucky's bill is at odds with the legal standard set by the Supreme Court in its 1973 Roe v. Wade ruling, which prohibits states from banning abortions before viability. But the Kentucky proposal is among a series of measures introduced by abortion opponents who hope the Supreme Court will be more receptive to limiting abortion rights now that Justice Anthony Kennedy, a key vote to preserve abortion rights, has retired.

Kennedy was replaced by Justice Brett Kavanaugh. Though Kavanaugh's record on abortion is limited, he did vote as a federal appeals court judge in 2017 in favor of delaying an abortion for a pregnant immigrant teenager in federal custody.

Meg Stern, left, and other escort volunteers line up outside the EMW Women's Surgical Center in Louisville, Kentucky, July 17, 2017. Dylan Lovan / AP file

In Iowa, a heartbeat law was temporarily blocked while a judge weighs whether it is unconstitutional. North Dakota's fetal heartbeat law was struck down as unconstitutional and the U.S. Supreme Court refused to review the lower court rulings.

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The effort to prohibit abortions in Kentucky once a fetal heartbeat is detected — which is around six weeks of pregnancy — would further cement Kentucky's reputation as "one of the most hostile states" to abortion rights in the country, Amiri said by phone.

The ACLU attorney added that the "vast majority" of abortions occur after six weeks of pregnancy and called a six-week ban unconstitutional under more than 40 years of precedent.

"Most women don't even know they're pregnant at six weeks," she said. "So this is a virtual ban on abortion."

The heartbeat bill was introduced Tuesday, opening day of Kentucky's new session, and one of the many sponsors expected it to be heard in committee on Thursday. Senate Majority Floor Leader Damon Thayer said he hopes the bill would get a Senate vote this week. It would still have to pass the GOP-led House before it would go to the state's anti-abortion governor, Republican Matt Bevin.

After Friday, lawmakers head home for a break before reconvening in early February for the rest of the year's session.

If it reaches the governor's desk, the heartbeat bill would give Bevin an opportunity to attach his name to a measure imposing stricter limits on abortions — a popular stance with his socially conservative base. Bevin, who has said he'll seek re-election this year, saw his approval ratings drop after he criticized public workers who opposed his efforts to change the state's struggling public pension plans. Kentucky and two other states — Louisiana and Mississippi — will elect governors in 2019.

Embry said the state's legal setbacks in the other abortion cases would not deter Kentucky lawmakers from pushing ahead with an even more restrictive measure.

"We're still going right ahead with what we think is the right thing to do," he said.

Thayer said the threat of another ACLU lawsuit also wouldn't hold up the bill in the Senate: "It's our job to make laws, to make policy, and that's what we're going to do."

Republican lawmakers in Kentucky have aggressively pushed bills to restrict the procedure since consolidating their hold on the legislature starting in 2017, even though two abortion-related laws have been struck down in the courts. Bevin's administration has appealed in both cases.

One of those laws, enacted in early 2017, had required doctors to perform ultrasounds and show and describe the ultrasound images to pregnant women, who could avert their eyes.

Another legal challenge arose over Bevin's interpretation of another law — passed about two decades ago — that required a Kentucky abortion clinic to have written agreements with a hospital and ambulance service in case of medical emergencies. Bevin's administration actions had threatened the state's last abortion clinic, EMW Women's Surgical Center in Louisville.

In a third case, lawyers for Bevin's administration and the ACLU argued over a lawsuit challenging a state law aimed at a common second-trimester procedure to end pregnancies. The law remains suspended pending a ruling by a federal judge.

Associated Press writers Adam Beam in Frankfort and Mark Sherman in Washington, D.C., contributed to this report.