Thousands of abortion opponents rallied on the Mall and marched to the Supreme Court in January. (Michael S. Williamson/The Washington Post)

San Diego physician George Delgado published anecdotes in 2012 from seven women who had changed their minds after taking one of two pills to terminate their pregnancies. Using an unproven protocol, he wrote, they were able to stop or “reverse” the abortions. The sensational claim was quickly embraced by conservative lawmakers pushing measures requiring clinics to inform women of this option.

Several states have now adopted a version of this legislation; Idaho is the latest, following Utah, South Dakota, Arizona and Arkansas. The laws have alarmed many medical groups, including the American College of Obstetricians and Gynecologists, which says no “credible” evidence supports the idea of reversing a medical abortion.

Now Delgado, who opposes abortion, has data on a new, larger group of women. His paper — appearing Wednesday in Issues in Law and Medicine, a journal with ties to an antiabortion group — looks at 754 patients who called an informational hotline in the United States from 2012 to 2016 after taking mifepristone, the first drug in a medical abortion, but before taking misoprostol, the second drug.

While his latest research suffers from some of the same weaknesses as his previous work, such as the fact that it consists only of observational case studies rather than being part of a rigorous clinical trial, it provides numbers sure to add to the abortion debate.

The women who called the hotline were referred to doctors who prescribed them progesterone, a hormone produced in the ovaries that helps prepare the tissue lining of the uterus for pregnancy and can be given orally, by injection or vaginally. Even critics of “abortion reversal” say there is some logic to this theory since the hormone is used to support pregnancies in a variety of situations, including to prevent preterm delivery, and is considered safe for both the woman and fetus.

Of the 547 patients who took progesterone within 72 hours of taking mifepristone and had outcomes that were known, there were 257 live births. Another four women remained pregnant with what seemed to be viable fetuses, but were lost to follow-up tracking after their 20th week of pregnancy. The overall rate of a pregnancy continuing, Delgado wrote, was 48 percent.

Fifty-seven of the women changed their minds again after taking progesterone. They took the second pill to complete a medical abortion or sought a surgical abortion — lending insight into just how difficult the decision process can be for some women.

Delgado concludes that the use of progesterone to stop a medical abortion “appears to be both safe and effective.”

Daniel Grossman, a professor at the University of California at San Francisco who focuses on reproductive health issues, has been one of the most vocal critics of abortion-reversal laws. He says “it makes some biological sense” that flooding the body with progesterone could counter the effect of the first abortion pill. But, he continues, there's also logic to the argument that progesterone is elevated in a normal pregnancy and so a pharmaceutical dose won't make much difference.

In addition, he said, “mifepristone by itself is not a very effective abortion-causing agent. If you use it just by itself there's a good chance the pregnancy will continue on its own.” Indeed, his own work has shown that women who took only mifepristone had a 25 percent chance of the pregnancy continuing. Such a finding is why the second abortion pill is typically given.

Grossman, whose research focuses on improving access to safe abortion in the United States and other parts of the world, said it's too soon to draw any conclusions from Delgado's latest paper. Whether medical abortions can be stopped or reversed is a question that should be studied, but in a rigorous way removed from the politics of abortion, he said.

“The really concerning part for me is that states are passing laws and essentially forcing physicians to inform women about a treatment that is experimental,” he said. Only a small fraction of the roughly 150,000 U.S. women who have medical abortions annually change their minds, he noted. “But it’s not zero, and I do think that women who change their minds should be given the best available information about what they should do.”

Delgado acknowledged that the journal in which his work appeared is co-sponsored by the Watson Bowes Research Institute, which is focused on antiabortion issues and therefore may be viewed more skeptically than other peer-reviewed journals. He said he would have liked to offer the paper to some mainstream publications but was not confident he would have gotten a fair look.

“Quite frankly, with all of the prejudicial statements a lot of people have been putting out, I felt like it would lead to editors not wanting to consider the article and delay things,” he said.

Delgado agrees that more research needs to be done. Once he secures funding, he said, he hopes to begin a randomized clinical trial in the next few months. He compares the skepticism about abortion reversal to the early questions about cardiopulmonary resuscitation when that technique was first introduced.

“It hadn't been studied formally in a big way, but we saw it was saving lives and had no alternatives. Were you going to wait when someone was dying in front of you?” he said.

Delgado, who is on the board of the American Association of Pro-Life Obstetricians and Gynecologists, said “the science is good enough that, since we have no alternative therapy and we know it's safe, we should go with it.”

Read more:

A Planned Parenthood branch demanded ‘a Disney princess who’s had an abortion.’ Then it had second thoughts.

5 interesting findings about U.S. abortions from a new report on the current science

FAQ: Are my frozen embryos safe? Everything you need to know about the freezer malfunctions.