Dr. George Delgado is a San Diego pro-life doctor who controversially claims to have reversed hundreds of medical abortions for women who have started the process and then changed their minds.

A medical abortion is used to end pregnancies up to 10 weeks, and involves taking two different medications. The first pill, called mifepristone, blocks the release of progesterone, which is essential for a healthy pregnancy. The second, called misoprostol, is taken 24-48 hours later and causes the uterus to contract and expel the fetus.

Delgado’s “reversal” involves intervening in a pregnancy before a woman takes the second drug to complete the abortion — by prescribing high doses of progesterone to counteract the effects of the first pill, a treatment he describes as “safe and effective.”

He says the idea came to him when a patient reached out to stop her abortion and that his abortion pill reversal website has helped more than 450 women “who want to have a second chance at choice” carry their pregnancies to term after using his treatment methods.

Read more: Promoting 'abortion reversal' is the latest tactic for the anti-abortion movement

But the mainstream medical community has slammed Delgado’s process as untested, and say his research is both poorly designed and unethical.

Dr. Daniel Grossman, an OBGYN and the director Advancing New Standards in Reproductive Health, a research group at the University of California, San Francisco that studies reproductive health issues to inform public policy, said that Delgado’s most recent study is devoid of evidence that his “so-called treatment” works.

“If there are some women who after taking the mifepristone change their mind, of course they should be able to access some kind of help. All of the evidence that we have so far indicates that the best course of action for those women is that we should just carefully follow their pregnancies and watch and wait,” said Grossman. “There's no evidence that any treatment progesterone or anything else will increase the likelihood that the pregnancy will continue.”

Read more: Medical community slams study pushing "abortion reversal" procedure

But Delgado thinks the concern over the use of progesterone to intervene in abortions is overblown and symptomatic of the political debate between pro-life and pro-choice medicine.

In an interview with VICE News, Delgado defended his work, which has now become the basis of several state laws requiring women seeking a termination be informed that abortion reversal is an option. “Instead of junk science, it should be called new science,” Delgado said.

Opponents like Grossman argue that Delgado's work fuels the misconception that women are somehow unsure of their decision to terminate their pregnancy. A 2017 study by Grossman’s colleagues at UCSF found that women who choose to have an abortion are more certain about that decision than for other medical procedures - like whether or not to have a mastectomy after a breast cancer diagnosis.

But for Rebekah Buell Delgado’s work was a godsend. Buell discovered she was pregnant at 19, had started the process of a medical abortion when she said she changed her mind. She contacted Delgado’s abortion reversal hotline after taking the first pill necessary to induce a medical abortion and was prescribed a course of off-label progesterone throughout her first trimester to in an attempt to counteract the effects.

“I thought that I would never really choose abortion. I thought you know, ‘I'm pro-life, I think abortion is wrong’,” Buell told VICE News. “But in that instant in that moment of panic. I thought, ‘Oh absolutely not. I'm 100 percent having an abortion quickly.’”

Read more: Trump officials discussed "reversing abortion" for undocumented teen

She carried her pregnancy to term, and her son Zechariah is now four and-a-half years old.

“I'm thankful for these doctors, I think that my son is here because of these doctors," Buell said, who has been testifying in state legislatures to advance abortion reversal laws. "But in some sense I think that they're also excited for what this means for the pro-life movement."

This segment originally aired April 24, 2018 on VICE News Tonight on HBO.