Wisconsin Gov. Scott Walker thinks ultrasounds are pretty cool. (AP Photo/Rainier Ehrhardt)

Thirty years ago, a doctor and a bioethicist wrote an article for the New England Journal of Medicine suggesting a woman seeking an abortion might change her mind after seeing an ultrasound of the developing fetus. The idea helped fuel a proposal -- mandatory ultrasounds before abortions -- popular among anti-abortion activists and infuriating to advocates for abortion rights.

The debate inflamed once again this week after Wisconsin Gov. Scott Walker, who signed a mandatory ultrasound law in 2013, described ultrasounds as “just a cool thing out there.”

Here's what the potential Republican presidential candidate told host Dana Loesch last week on the The Dana Show:

We signed a law that requires an ultrasound. Which, the thing about that, the media tried to make that sound like that was a crazy idea. Most people I talk to, whether they're pro-life or not, I find people all the time who'll get out their iPhone and show me a picture of their grandkids' ultrasound and how excited they are, so that's a lovely thing. I think about my sons are 19 and 20, you know we still have their first ultrasound picture. It's just a cool thing out there.

Walker's comments drew criticism from pro abortion rights groups. Planned Parenthood President Cecile Richards called his remarks "appalling" and said,"Women are very clear that forced government ultrasounds are not 'cool.'" (Walker cut funds to Planned Parenthood in Wisconsin.)

The spat underscores a national trend to require women who want abortions to first undergo an ultrasound. Ten states have adopted the requirement, which can add up to $300 to the procedure. Wisconsin, Texas and Louisiana have taken it further, requiring physicians to show women the images, according to the Guttmacher Institute.

“Since routine ultrasound is not considered medically necessary as a component of first-trimester abortion, the requirements appear to be a veiled attempt to personify the fetus and dissuade a woman from obtaining an abortion," researchers at the Guttmacher Institute wrote.

Defenders of the measure say ultrasounds can prevent expectant mothers from later facing regret. “The manipulation of language has long been one of the hallmarks of the pro-choice position,” according to an argument on the Catholic Education Resource Center website.“But with ultrasound, words no longer matter so much: The abstract melts into the concrete and the personal. This powerful emotional appeal will continue to grow as 3-D ultrasound enters the mainstream.”

Regardless of the philosophical debate, the practical question is whether mandatory ultrasounds can actually impact a woman’s decision. Not really, according to the largest study ever conducted on the policy.

Last year, researchers pored over 15,575 medical records from an abortion provider in Los Angeles. Nearly all patients who saw a sonogram still opted to terminate their pregnancy -- and those who changed their mind reported entering the clinic with uncertainty.

Technicians asked each patient how she felt about her choice. Women who gave “clear and confident” responses were considered to have “high decision certainty," the study authors wrote. Those who expressed sadness, anger or ambivalence showed “low” or “medium” certainty.

Each patient underwent an ultrasound. Nearly 43 percent chose to see the sonograms. Of those who saw the images, 98.4 percent ended their pregnancies -- compared to 99 percent of women who chose not to view the photographs and ended their pregnancies, according to the journal  Obstetrics & Gynecology.

The 1.6 percent who decided against abortion, the authors noted, all fell into the categories of “low” or “medium” certainty.