In 2004, he traveled to Nebraska to pursue certification in Natural Procreative Technology, a Catholic-friendly approach to women’s reproductive health. Developed by an anti-abortion OB-GYN named Thomas Hilgers who was also inspired by ‘‘Humanae Vitae,’’ ‘‘NaProTechnology’’ eschews most forms of birth control and fertility treatments and relies instead on tracking widely used ‘‘biomarkers’’ like cervical mucus and body temperature. At Hilgers’s Pope Paul VI Institute in Omaha, Delgado learned to use progesterone to treat issues like repeated miscarriage and postpartum depression. The next year, he moved from the Bay Area to San Diego to join Culture of Life, a Catholic clinic founded by local longtime anti-abortion activists named Ken and Marie Finn.

In 2009, Delgado says, he received a call from an acquaintance who ran an anti-abortion ministry focused on counseling women outside abortion clinics. A young woman in El Paso, Tex., had just taken the first pill to begin a medication abortion and immediately regretted it. She found the activist’s phone number online and called in a panic. Was there any way to undo her mistake? By this time, Delgado had been using progesterone for years to treat women dealing with fertility issues. And he knew that mifepristone, the first drug in the abortion-pill protocol, works by blocking progesterone from the uterus. Couldn’t an extra dose of progesterone overcome the mifepristone? Within hours, he sketched out a plan to inject the woman with 200 milligrams of progesterone and to con­tinue giving the progesterone until the end of the first trimester. Through a national network of NaProTechnol­ogy-friendly doctors, he quickly found a doctor in El Paso who had the right form of the hormone available in her office and was willing to try it. The fetus survived, and the baby girl was born healthy.

Delgado later found out that a doctor in North Carolina, Matthew Harrison, had received a similar call from a crisis pregnancy center in 2006 and independently made the same guess about progesterone counteracting the effects of the mifepristone. That fetus, too, survived, after the mother received progesterone injections through her 26th week of pregnancy. ‘‘I didn’t make a whole lot of noise about it because I knew that people would try to write it off,’’ Harrison says. ‘‘It’s not like we have women every day knocking on our door to reverse abortions.’’

Over the next few years, however, Delgado and Harrison occasionally heard from doctors and activists who wanted to know more about their interventions. In 2012, Delgado put up a simple website and opened a hotline for women to call for information about reversal. That year, he and Mary Davenport, a doctor in the Bay Area, started contacting a few other doctors who had performed reversals with progesterone. They soon published a small case series in the journal Annals of Pharmacotherapy. The article, just four pages long, describes seven pregnancies treated with progesterone after mifepristone. Two of the abortions completed, but four of the fetuses survived. (One woman evaded the doctors’ attempts to follow up.) ‘‘The experience of these patients suggests that medical abortion can be arrested by progesterone injection,’’ Davenport and Delgado concluded. ‘‘If further trials confirm the success without complications of this or similar protocols, it should become the standard of care for obstetrician-gynecologists, family physicians and emergency-department physicians to attempt mifepristone reversal on patient request.’’

Delgado’s hotline received just 28 calls in all of 2012. But the volume increased over the years: 200 calls in 2013, more than 400 in 2014 and more than 600 for each of the last two years, according to the reversal program’s executive director, Sara Littlefield. Today 17 nurses across the country take shifts answering the calls, which are routed to their cellphones. When a call comes into the hotline, the nurse’s job is to connect the caller as quickly as possible with a local doctor willing to administer the reversal protocol. The program has a network of about 350 doctors who are familiar with it and prepared to see patients. If the caller doesn’t live within driving range of one of those providers, the hotline nurse immediately starts calling local doctors and hospitals to explain what reversal is, hoping to find a sympathetic provider. Catholic hospitals are usually a good place to start.

Within the last few years, Delgado and Harrison have become something like celebrities within the anti-abortion movement. Conservative media outlets report on reversal at length in flattering terms, and several of the women who have undergone the procedure have begun telling their stories in public, too. Delgado has delivered presentations at events hosted by the National Right to Life Committee and the American Association of Pro-Life Obstetricians and Gynecologists, where he serves on the board. Harrison and Delgado also started promoting ‘‘emergency abortion pill reversal kits,’’ glorified instructional pamphlets intended for emergency rooms and crisis pregnancy centers. One fan gave Harrison a T-shirt that read ‘‘Reversed RU-486. Now reverse Roe vs Wade.’’

A vanishingly small percentage of women decide they want to reverse a medication abortion halfway through. In fact, regret is quite rare when it comes to abortions in general. A 2013 study found that although women experienced a wide range of often conflicting responses to the procedure, relief was the most common emotion one week after. A later study found that women who had abortions were also confident in their decisions beforehand — more confident than people who decide to get reconstructive knee surgery, for example. ‘‘Most women are certain of their decision when they present for care,’’ says the study’s lead author, Lauren Ralph, an epidemiologist at the Univer­sity of California, San Francisco. Their certainty is largely unchanged by waiting periods and mandated counseling, which suggests ‘‘women do not change their minds.’’ Ralph also found that women who do experience uncer­tainty are more likely to already believe a myth about abortion, such as that it causes breast cancer.