Lawmakers in several states are considering requirements for doctors to inform women seeking medical abortions about an unproven procedure called “abortion reversal.”

Doctors' groups oppose the bills because of flawed science and ethical concerns. There is no evidence the procedure works and little information about its safety.

The procedure involves shots of the hormone progesterone given if a woman changes her mind after the first step of a medical abortion.

Since 2015, Arkansas and South Dakota have enacted laws requiring doctors to tell women about it. An Arizona law was challenged in court and later repealed. Bills are under consideration in Colorado, Indiana, North Carolina and Utah.

“It's really concerning that legislatures are passing laws interfering in the doctor-patient relationship and forcing them to tell women about an experimental therapy that is unproven,” said Dr. Daniel Grossman, a professor in the Department of Obstetrics, Gynaecology and Reproductive Sciences at University of California, San Francisco.

About a third of women who seek abortions in early pregnancy choose medical abortions because they want a less invasive procedure than a surgical abortion.

In the United States, medical abortion involves taking two drugs. The first - mifepristone - thins the lining of the uterus and loosens the connection between the embryo and the uterine lining. The second - misoprostol - softens and opens the cervix and causes contractions to push out the pregnancy.

The second drug is taken at home hours to days after the first drug.

Women rarely change their minds before completing the treatment. Doctors are required to report such information to the manufacturer of mifepristone. Between 2000 and 2012, less than 0.004 percent of women taking mifepristone changed their minds, Grossman said.

“Women are very sure of their decision by the time they go to the abortion clinic,” Grossman said.

Progesterone is legitimately used to prevent pre-term birth in women who are at risk of early delivery. Some claim it can counteract the effects of an unfinished medical abortion.

Dr. George Delgado in San Diego, California, is the chief advocate. He is medical director of Culture of Life Family Services, described as “the 'flip-side' to Planned Parenthood” on its website. The clinic “offers true reproductive health care and abortion alternatives to women,” the website says.

Delgado published a paper in 2012 about six women who had taken mifepristone, the first medication in the two-part medical abortion, then had a series of progesterone shots. Four of the six women had healthy babies. The other two aborted.

Delgado says he has given progesterone to several hundred other women who also changed their minds after starting a medical abortion. He says he has a 60 to 70 percent success rate and hopes to publish the results in a peer-reviewed journal.

“If there's a way to give them a second chance at choice, it will be a wonderful thing,” Delgado said.

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Delgado's study is not considered high-quality research because it is small and there was no comparison group. Researchers have questioned whether the women were given adequate information about the experimental nature of the procedure.

For women who change their minds after taking mifepristone, doing nothing and waiting to see what happens may be just as effective as progesterone shots.

That's because mifepristone alone doesn't work very well without the second drug. Thirty percent to 50 percent of women who take mifepristone alone will have continued pregnancies, according to the American Congress of Obstetricians and Gynaecologists. (Delgado disputes this and says the survival rate of embryos after mifepristone is much smaller.)

Progesterone shots are generally safe but can cause swelling, irritation and other side effects. The cost of pushing an experimental procedure into widespread use also raises ethical questions, Grossman said. The injections and doctor visits involved can cost up to $1,000.