Seven states - Alabama, Idaho, Indiana, Kansas, Louisiana, Nebraska and Oklahoma - have put laws into effect in the past several years banning late term abortions, based on questionable medical research suggesting that a fetus feels pain starting at 20 weeks of gestation.

Another state, Georgia, has such a law scheduled to go into effect in January, although a lawsuit over the measure is pending in state court. Arizona also passed a similar law banning abortions 18 weeks after fertilization, but it has been blocked by federal courts.

Texas would be the largest state to pass such a measure, although Perry, a Republican, did not outline details of what he envisioned in a bill.

"We cannot, and we will not, stand idly by while the unborn are going through the agony of having their lives ended," Perry, a failed 2012 Republican presidential candidate, said in prepared remarks for a news conference on Tuesday.

Opponents of such proposals say they are based on unfounded science.

"And yet we see these bills proliferating across the country," said Elizabeth Nash, state issues manager for the Guttmacher Institute, a research group that supports abortion rights. "It looks like this issue is one that state legislatures are going to be wrestling with for another year."

Arkansas, Virginia, Wisconsin and South Dakota are also expected to introduce such bills, Nash said.

The position of the American College of Obstetricians and Gynecologists is that there is "no legitimate scientific information that supports the statement that a fetus experiences pain."

The group notes that certain brain and neurological developments, including neurotransmitted hormones, have to be in place to perceive pain. Animal studies show these hormones are developed only in the last third of gestation.

Some anti-abortion arguments on fetal pain are taken from research by Kanwaljeet J.S. Anand, a professor of pediatrics, anesthesiology, anatomy and neurobiology at the University of Tennessee Health Science Center.

Anand has said that prenatal surgeries are routinely done with anesthetic, and that despite ACOG's 2005 statement, "the consensus opinion seems to be in favor of the fact that fetuses do perceive pain."

In Texas, the Legislature convenes in January with Republican majorities in both chambers. In 2011, Perry successfully pushed a measure requiring women seeking an abortion to first get a sonogram.

(Editing by Paul Thomasch and Christopher Wilson)

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